Last fall, Sahir brought his Miata to Pineview and allowed Josh and I to drive it. Sahir had just won the C4 class of the Pineview Challenge Cup the week before and was on pace. Josh is a two-time Challenge Cup overall winner and one of the fastest people I know. I haven’t won any championships, but I’m a self-proclaimed Miata and Pineview specialist, and I go fast when those two things are combined. So we all know the track really well, but our driving styles differ. I wanted to see by how much, and what we could learn from each other.
I imported all the laps in Race Studio and threw out the first lap of each session. For some reason, the first laps create fast sector times that are impossible. Then I created a track map with seven sectors. Formula 1 uses three sectors, MotoGP uses four. I wanted to get more granular, and see where each driver was doing their best. This put the track divisions on the straights between T2-T3, T5-6, T7-T8, T10-T11, T11-T12, and T12-T13. See the shitty image below.
I then used the Split Report feature to see how we did in each split. If you click the History tab on each sector, this gives you a histogram chart that makes it easier. A long green bar is a slow sector. A short red bar means the fastest sector time. Check it out. (Yellow bars are rolling laps, ignore for now.)
Run 3 is Sahir. He does six hot laps (laps 2-7) with a best lap of 1:18.537. He sets the fastest time in the sixth sector, the Blind Hairpin.
Run 4 is Josh. You’ll notice he only puts in two laps with a best lap of 1:18.873. In an unfamiliar car, in two laps, he almost matches Sahir’s time (and only .1 seconds off Sahir’s PV Cup wining lap). Josh kills it in Sector 1.
Run 5 is me. I do seven hot laps with a best lap of 1:17.674. I set the fastest time in the remaining sectors. Enh, I’m fast in Miatas, and on this track in particular.
As good as any of us are individually, if you put all of our best sectors together, we’d do a 1:17.192! That’s half a second faster than I went, and about 1.5 seconds faster than Sahir and Josh. OK then, what can we learn from each other?
In the following speed traces, Josh is black, Sahir is blue, and I’m red. I’m using the two fastest laps from each person. First let’s look at Josh, he’s magic in Sector 1. Notice on the bottom graph (time-distance) that one black squiggle that’s below all of the other colored lines. He has a higher minimum speed in T2, and puts some time in his pocket.
Next is sectors 2-5, and I’m fastest at three points in particular, circled in orange: In T4, my line allows me to get to the throttle earlier; In T7, I use a straighter approach that allows me to brake deeper and harder on the entry; In the Knuckle, I take a deep double-apex line that keeps my speed longer. Interestingly, we’re all very even in the Uphill Esses (notice that all the lines in the bottom graph are basically horizontal from 1700′-2400′). Nobody is winning that part.
Sahir is fastest in Sector 6 by .01 seconds. The time-distance graph has a dip at 3500′ which corresponds to his speed advantage at that point. He’s simply braking later than us chickens, and that’s understandable because the Blind Hairpin has claimed a couple cars on the berm.
In the final sector I gain a little time by braking later (notice the height of the red lines at 4100′), and I get another boost of speed right between Turns 14 and 15 at 4500′. (Ignore where the cursor is.)
None of us are professional drivers, and we can all improve by simply looking at what each other is doing. But this is really only possible by using data. It’s a bit late to make a New Year’s resolution, but if you aren’t using data, make a resolution to do that now instead of next year. I’ll be your accountability partner!
This blog post is going to sound like a pissy rant. Fuck it, I’m due one.
Social media has created a dangerous situation where opinion is more important than fact. It’s almost like whoever yells the loudest and most often wins. And this brings me to a tired topic on Trackable Miatas. What’s faster, a 205, 225, or 245?
It’s a circular topic. At some point someone will chime in that it depends on power. Someone else will say you have to put a 205 on a 8″. That only lasts until someone says 205 is better on a 9″. Then another will say that 205s are proven to be faster than 225s or 245s on California tracks. As if tracks are different there? I’ve raced at Laguna Seca, Willow Springs, Thunderhill, and Sears Pt and they are no different than WGI, PittRace, NJMP or other east coast tracks I’ve raced at.
Next someone who is sick of being tread on will say, where’s the data? And all those people fall back on “it’s a proven fact,” without showing any. Honestly, I had to leave Trackable Miatas for a while because it’s the same people shouting the same nonsense without a shred of data to back it up.
It really is a bunch of hooey, and I’m just getting in a groove. First off, the notion that 205 tires are faster is flawed by the very fact that 205 tires aren’t all the same width. A 195 RS4 is wider than a 205 RE71R. A 205 Hoosier is wider than a 225 NT01. What 205 tire are you talking about? And then there’s the whole wheel width variable, as if offset, weight, tire pressure etc, weren’t factors to consider. And then some tracks are high speed and some are more about cornering.
I really have to question if any of the people that claim 205s are faster have done back-to-back testing using the same compound tires of different widths? Have they swapped wheel widths (same weight, same offset) on the same tire? If they have, they aren’t sharing the data.
Well, I can understand that, I haven’t either. But I’ll open the door just a tiny bit and shed some light on this.
Last Memorial Day four of us got together in Miatas and tested tires. Me, Alec Fitzgerald, Alyssa Merrill and Davey Thai got together in four Miatas and tested 10 sets of tires. We divided up the tires so that there would be some crossover.
Alyssa tested Hoosier A7s and R7s in 205, Maxxis RC1s in 245 and Hankook Z214 C51 in 2o5
I tested 225 RS4s on 8″ and 9″, and 245s on 9″, RE71Rs, and both Hoosiers
We did this as scientifically as we could, recording air, track and tire temperatures, set optimal pressures, and ran multiple redundant sessions to gather data. I’m not going to share the lap times and data with you because information like that isn’t free. But I’ll give you this chart: same driver, same corner over 200′ of distance at 20′ intervals, two runs averaged, 225 RS4 on 8″ and 9″, 245 on 9″, and some other tires mixed in.
Years ago there was a site called solomiata.com, and it was the best resource for people who wanted to tune their 1.6 Miatas. Later the author added information for 1.8s. The site was down, it was back up, it was down, and now it lives over here.
The Solomiata recipe for cheap horsepower was:
Advance the timing 4 degrees, for about + 2 hp.
A cat-back exhaust, for about 4-5 hp.
Replace the AFM with a larger flapper valve from a RX7. The standard Miata flowmeter is too small to flow at high RPM, and so this added 5 hp above 6000 RPM.
Aftermarket header for another 3-4 hp.
Add a programmable ECU, larger injectors, and an adjustable fuel pressure regulator.
Shave the head .010″ for about 4 hp.
All of that would get you a maximum of 115 hp at the wheels. I think a more realistic estimate is 108-112 hp based on most stock 1.6 Miatas dynoing around 92 hp stock, and our cars being a lot older at this point.
The modern Solomiata formula
That was then, what do people do now? Swap in a VVT 1.8. A bone stock NB2 motor will put out similar horsepower as the Solomiata formula, and way more torque. I drove Napp Motorsports’ VVT swap back to back with my well modified NA6. My motor has only 5 hp less, but the torque difference was astounding, like it was a completely different car. It was the lightbulb moment where I was like “I made a huge fuggin mistake.”
However, if you aren’t ready to take the motor swap plunge, here’s the modern Solomiata formula for a 1.6 Miata.
Standalone EFI. I got a Megasquirt PNP2, which is about $800, but these days you can buy a Speedy EFI unit for half that. It even comes with a variable TPS (the 1.6 Miata has an on/off throttle position sensor). A standalone EFI combines steps 1, 3, and 5 from the Solomiata formula.
Cold-air intake. If you want to keep the stock airbox, get a cowl intake (Randall or DIY a snorkel). If not, find someone to 3D print you an intake.
Cat-back exhaust. There are many to choose from. Optionally replace the catalytic converter with a high-flow cat for another 1-2 HP. Your OEM cat is worth over $100 at any scrap yard, so that will defray the cost.
My car with only a MS PNP2, cone filter, and cat-back exhaust pulled 106 hp on a Dynojet. I hadn’t decked the head at that point, but if I had, I’d be right in the Solomiata ballpark.
All of these mods can be done cheaper and easier than a motor swap, with about the same result. You won’t have shit for torque, but you’re used to that, right? You might have noticed I didn’t add a header to this list. The reason being, that’s specifically a 1.6 part and won’t work on a 1.8. You can do all of the mods above and still come to your senses and do a 1.8 VVT motor swap.
Up to this point you won’t need to dyno tune your car, either. You can use the EFI’s base map, as its programmed for mild bolt ons. But if you modify the car further, you’ll need to tune the EFI. And that’s where things get difficult. Not the tuning itself so much, but because the 1.6 head doesn’t flow well. Quality control on these heads wasn’t great, and there’s a lot of core shift between different heads, and the port geometry could be improved (and later was).
You might think that the shorter stroke means you could go after high RPMs, but if you do that, then the oil comes out of the hydraulic lash adjusters. So there’s a low ceiling on how far you can tune a naturally aspirated 1.6, both bottom end, and top end.
This is a smart place to stop modifying your normally aspirated 1.6 and look for a junkyard NB2. Unless you need to replace a head gasket or remove the head for some other reason, this is a smart place to stop reading.
I don’t care, I’m tuning a 1.6
If you’re going to modify a naturally aspirated 1.6 Miata any further than this, then you’re already beyond reason. If logic worked, it would have worked already. But misery enjoys company, so thanks for joining the club.
OK, so let’s do this. The next thing you need to do is pull the head. An older engine may need a valve job, and you can get a lot of things done at the same time.
Number all the valves and their locations and remove them (socket and hammer trick.) Clean up the ports with a Dremel tool. It’s free HP for a bit of your time. Remove casting flash, smooth any hard edges around the plunge cut, and blend the web between the ports. Polish the exhaust side, but leave the intake side a bit rougher.
Take the head to a machinist and have them measure the valves and springs. Make sure to order new OEM valve guide seals. You might consider +1mm intake valves, this will add about 4 hp and torque. In any case, have them do a valve job.
Have the machinist deck the head .040″ to bump up compression by one point. I’ve heard of people safely taking off more than that, but on Premium pump gas, you really don’t want to go much further. This will also retard cam timing a few degrees, which also helps. FWIW, there’s no bigger bang for the buck than decking the head, it cost me all of $50. If you need to replace a head gasket at any time, just deck the head and start using premium gas. I’d do this even on a bone stock NA Miata.
Next is cams. The cheap way is an exhintake cam, modifying a MX-3 cam and putting that on the intake side. This gives about 8 hp when properly tuned. Or you can get a Kelford cam and double it. I went with a 203-B cam, which is about max for the street. A larger cam will have a rough idle, and you’ll need to replace valve springs, retainers, etc.
With all that work into the 1.6 head, put on an aftermarket header. I have a Racing Beat in my race car and a Raceland in my street car. One of the welds failed on the Raceland, and the header was replaced for free. However, it was a hassle, and when you look at the difference in quality between Racing Beat and Raceland… well, you get what you pay for.
Tuning is a must at this point. Reprogramming the ECU can range from free (your laptop) to $600 or more (dyno operator).
This is pretty much where my car sits right now, with 129 hp on a Land and Sea dyno (which reads like a Mustang). This equates to about 145 hp and 122 ft-lbs on a Dynojet. An NB with all the bolt ons will have slightly less horsepower and more torque, and overall similar performance.
Where next, NA6?
OMFG you’re still reading? The smart people left the room a while ago. They swapped in a NB2, Honda K motor, Ecotec, or used forced induction.
Speaking of forced induction, the Miata 1.6 engine was originally designed for a turbo. Back then people would complain about turbo lag, but modern turbos with standalone engine management offer instant throttle response, fat torque, and a top end rush. My teammate’s turbo NA6 turbo is in my garage right now, so I know what a good turbo feels like.
But I don’t want a turbo. I can’t answer that logically. Somehow I’m keen to get a supercharger, even if it’s not as good. And then part of me just wants to see how far I can push the normally aspirated 1.6 envelope. I guess I’m a glutton for punishment and disappointment.
So let’s say we continue this normally aspirated experiment, just as a thought exercise. Where do we go next?
Intake manifold. The NA6 intake manifold is a single cast piece, so you can’t pull it apart and polish the runners or add volume with a plenum spacer. There are some things that can be done here. None of it is money well spent, but that ship sailed a long time ago.
Extrude hone. This is basically forcing liquid sand through the manifold, which polishes the places you can’t reach. I would expect at most a 5% gain in power for $500.
Manifold spacer. A piece of phenolic machined to the dimensions of the intake manifold runners would help lower intake temperature and provide longer runners. I’d probably have to space things out in the engine bay, and install longer studs in the engine. And there’s the issue of the injectors now being further from the port which might not be good for atomization.
Skunk2. The Skunk2 intake manifold is available only for the 1.8 block, and adds 5-10% more power on the top end. Could this be adapted to a 1.6 with a manifold spacer? Cylinders 1 and 4 would need the ports angled 6mm in, and the injectors would have to be welded into the manifold (they are in the head on the 1.8).
Log manifold. These are primarily for boosted cars, but might unlock some N.A power. The one from RZ Crew is beautiful, if nothing else. The intake runners don’t wrap around the bottom, and might be shorter than stock, which wouldn’t help.
NB6 head – In the USA, the 1.6 was last sold in 1993, but in Europe and Japan, they continued to sell the smaller motor. When the 1.8 went from NA to NB, so did the 1.6. The NB6 got the better port geometry, solid lifters, and I believe there’s a square-top NB6 intake manifold as well. I have the cam for the NA6, which has a different profile for the HLAs, so I’m probably not going down this route. But if someone were starting from scratch, this is a better starting point for 1.6 insanity.
Ram air. I’ve actually built one of these airboxes, and it worked out to 1% power gain hp at 100 mph. At less than 100 mph, and at partial throttle openings, there was no change in manifold pressure. But, pinned WFO doing the ton, I watched 4″ of water drop (intake manifold pressure change). This was later verified on a dyno with a leaf blower, adding 1 hp. My intake has gone back and forth, and is currently not a ram intake, but I might go back to it again if I go to Watkins Glen regularly and desperately need 1 hp.
ITBs. Some people have used Toyota AE101 intakes, other have used a more plug and play version from Jenvey. There’s a long thread on Club Roadster where a guy threw everything at a 1.6 including Jenvey ITBs and got 158 HP IIRC. My research says this is worth about 10% more power, and that’s after a lot of dyno tuning.
Displacement – There’s a cheap stroker kit, it’s called a 1.8 swap. So what options are there for boring the block? Most of the aftermarket big-bore pistons are low compression, meant for boost. On the other side are 12:1 pistons that would now be 13:1 on a decked the head. Yikes! Somewhere in the middle is a unicorn big-bore standard compression piston with my name on it.
The little things. I haven’t fooled around with cam timing yet. I might need new injectors. People say coil-on-plugs will do something more than nothing. Mathematically, the throttle body flows enough, but maybe boring it out would help.
In reality, it’s unlikely I’ll do any of these. My money is better spent on anything else. Just the same, stay tuned, I might venture further down the path of disappointment.
A friend and his dad are just getting into track driving, and building up their NA8 Miata for that purpose. It got me to thinking, if I was in that situation, knowing what I know now… what would I do, and in what order?
Phase 1: Track Ready
The first thing is a car that’s track-legal, and safe. It’s also never too early to start collecting data.
4-point Rollbar – Most tracks and HPDE organizations require this.
Brakes – StopTech 309 pads and high temp brake fluid. The StopTechs don’t have a lot of bite, but are great on the street, and handle track temps OK. Their big selling point is price, sometimes I find them for less than $40.
Tow straps – Baby teeth are fine, but if you removed them, you need something to attach a tow hook to, front and rear.
Data – If you’re just getting started, a phone app is fine. You’ll want to add a 10 hz bluetooth antenna eventually, or better yet, get an Aim Solo or similar device made for motorsports.
Phase 2: Mechanical Grip
Drive the car like that for a few events. Resist the urge to put on sticky tires; All-season tires and stock suspension are learning aids. But once you can slide the car through every corner, it’s time to get more mechanical grip. This is a big step, and requires several things at once.
Tires – A Miata on sticky tires is what momentum driving is all about. I like Hankook RS4s for their predictability and durability, but they aren’t super sticky. At the other end of the spectrum are take-off Hoosiers and Toyos from Spec Miata racers, which is an economical way to go fast. And there are a lot of 100-200 TW tires in between, the tradeoff is always between grip and longevity.
Wheels – The stock wheels will hold you back. A 15×8 +35 wheel and 205 tire will fit with no modifications. If you roll the fenders, you can use 15x9s and run 225s, which is the current go-fast formula.
Hubs – Sticky tires break stock hubs. The fronts are usually the ones to go, but my race car broke at the rear. I have BroFab hubs on my street car and Miatahubs on my race car. There are other options, and some people simply throw out the OEM hubs every year.
Suspension – Shocks with stiffer springs and NB top hats. Coilovers so you can corner balance. Stiffer front sway bar and a bracket so you don’t tear the mount. If your car has a lot of miles, it might need new suspension bushings. Ugh.
Alignment – You’ll probably need extended lower ball joints to get enough front camber, otherwise you’re going to wear the tires out. Get a proper track alignment.
Seat and belts – At this point you’re going to be thrown side to side more, and a race seat is nice. You might also want a 5-7 point harness, and with that comes the requirement of a Hans device.
Phase 3: Hurt Machine
Bolt-on power and areo are next on the list.
The usual suspects – A cold-air intake, header, and cat-back exhaust will each unlock about 5% power, which is still doable on the stock ECU. You might bump the timing a few degrees and do other minor tuning tricks if you haven’t already.
Maintenance items – Some performance gains can be had if you’re replacing parts. If you need a clutch or throwout bearing, then do a lightweight flywheel at the same time. A 10-lb reduction in flywheel is worth about 7 hp in 1st gear, 3 hp in 2nd gear, and 1.5 hp in 3rd gear. If you need to pull the head for any reason, deck it .040″. That’ll cost about $60 and you’ll have to use Premium gas, but it’s the best bang for the buck. A high-flow catalytic converter will get 1-2 hp, but you can sell your OEM cat for almost the same price.
Front aero – Airdam, undertray, ducted radiator, and hood vents. You have to do all of these at the same time because they are related. Brake ducts are optional, but easier to do that now than later.
Rear aero – For a car that does more street than track, I like the looks of a spoiler. It needs to be at least 4″ high, preferably 7-8″. For a dedicated track car, use a 9 Lives Racing wing and add a splitter to the undertray.
Misc aero – Fender vents, side skirts, flat bottom, diffuser, etc., are all worthwhile. Just say no to vortex generators.
At this point the car is the Trackable Miata build many people aspire to, and it’s a damn fast car. The engine is still basically stock, and you can beat on it all day. You can also beat on average drivers in Porsches, BMWs, etc. This is a machine that can hurt a lot of feelings.
But if you want to run with a well-driven Porsche, Corvette, or whatever, you need more power. This is the point where you decide if you’re going to NA tune the engine on a standalone, swap the engine, or go forced induction. Those decisions are like diets, religion, and politics: you don’t bring them up in pleasant company. And so I’ll leave my opinion out of it, except to say that anyone tuning a normally-aspirated 1.6 deserves their beatings.
The total coefficient of drag on my racing Miata (hard top, airdam, splitter, wing) was measured precisely at Cd .48. Where does that drag come from, and how can you reduce it?
The following table shows estimates of where that drag comes from. You’ll notice a splitter reduces drag, but every other feature adds to it. This data is largely from Katz, but I’ve supplemented this with some Miata values and racing parts (airdam, splitter, 9LR wing) and included a value for the windows being open (we are racing, after all).
Rear wheels + suspension
Front wheels + suspension
Underbody and chassis
Total drag coefficient
Parts of the car that contribute to drag, and how much.
There are lots of ways to reduce drag. One way is to use a fastback, which reduces the drag in three places: bodywork, rear surfaces, and open windows (my fastback is narrower and considerably less air goes in the windows).
My fastback reduced drag by .07 to a Cd of .41. What does a 15% reduction in drag do for lap times? I’ll run a quick simulation in OptimumLap (2375 lbs, 125 hp, 1.15 grip).
Miata lap times changing only the drag value.
Right away you can see that drag reduction at a course like Pineview (or autocross) is nearly worthless. At a medium-speed track like New York Safety Track, it amounts to less than half a second. But at a high speed track like Watkins Glen, drag reduction is worth 1.2 seconds! So the value of drag reduction depends entirely on the venue.
For endurance racing, drag reduction is almost always worthwhile, but you need to make large gains. A 15% reduction in drag works out to only 2% less fuel usage at Watkins Glen. But if you’re right on the cusp of a 1:55 stint time, that’s huge.
Every once in a while someone talks to me about reducing the drag from their wing, or choosing one single-element wing over another because it’s more efficient. If you look at the table above, my 9 Lives Racing wing only adds .03 drag. Even if you could reduce your wing drag by 20% (doubtful), that would be a .1 second per lap at WGI and .03 seconds at NYST. Seriously, there are bigger fish to fry!
When setting a course for drag reduction, start at the bottom of the table, where the biggest items are, and work your way up.
Wing Angle, Efficiency, and Downforce
If you have a wing, your next question might be, is it better to run less angle and have a more efficient wing, or more angle for downforce? Assuming you can set the car up to handle equally in each situation, which would be fastest?
Let’s run another simulation. I’ll use my data for a 9 Lives Racing wing and use three values: 0-degrees AOA representing the most efficient setting, 10 degrees with a 1/2″ Gurney flap representing the most downforce and drag, and 5 degrees no Gurney to split the difference. I’ll use the same car and the same three race tracks.
Zero angle of attack, L/D 14:1, Cd .461
5 degree, L/D 13:1, Cd .48
10 degree, 1/2″ Gurney, L/D 8.5:1, Cd .52
Wing angle and lap times
What’s interesting to note here is that the most efficient setting (zero degrees angle of attack and no gurney flap) is the slowest at all tracks. The setting with the most downforce (10 deg AOA, 1/2″ Gurney) is fastest at Pineview and NYST, but not at WGI.
The best wing angle for your car is obviously track dependent, but if I was going to set it and forget it, I’d run the wing at 5 degrees and add a 1/4″ Gurney flap. I’m not going to run that simulation for you, I have to keep some speed secrets for myself.
How much downforce does your wing make? Mathematically, you can calculate downforce using: downforce = 1/2p * A * Cl * V^2. If that means anything to you, then you don’t need this website. If that calculation scares the shit out of you, read on.
You can break this formula into four parts:
1/2p – I’ll simplify this as a constant value of .00119. That’s all you need to know about 1/2p. (OK, someone actually asked about this, it’s air density, which changes due to elevation, temperature, and humidity. If you want to calculate the downforce at sea level, on a cold and wet day, versus a hot and sunny day in the mountains, go ahead. Or just accept my static value and move ahead.)
A – This is the area of the wing in square feet. If you have a 64″ 9 Lives Racing wing (10″ chord), then your area is 4.44 square feet (64″ x 10″ / 144 ). If you have a 72″ 9LR wing, that’s 5 square feet.
Cl – This is Coefficient of Lift. It’s a tricky value because it changes with different shapes of wings, how fast you’re going, the wing angle, and turbulence. For the time being, you can use a value of 1.0. I’ll explain later why this is a good value.
V^2 – Velocity in feet per second, squared. For this you need to know that 1 mph = 1.46667 feet per second.
OK, so let’s figure out about how much downforce a 64″ x 10″ wing produces at different speeds. Three things will remain constant, the 1/2p value, the wing area A, and the coefficient of lift, Cl. Multiply all those factors together and you get a value of .00528836. Now all we need is to multiply .00528836 by the velocity in feet per second, squared.
Downforce at various speeds, 9LR 64″ wing, Cl 1.0
How Much Added Grip?
If we assume that tire grip is linear, we can calculate the amount of grip you gain at different speeds. Downforce helps lighter cars more than heavy cars, because the percentage gain is greater. I’ll use the same wing and speeds to illustrate this.
2400 lb car
3000 lb car
Grip increase at different speeds using the same wing.
Coefficient of Lift = 1.0
In the above calculations, I chose a Cl value of 1.0. In reality, a good single-element wing in free-stream air, at high velocity (high Reynolds number), can create 50% more downforce than that (Cl 1.5). Meaning that if we can place the wing in non-turbulent air, and drive faster (creating a larger Reynolds number), the wing will be at peak performance.
In the real world, you can’t get to peak performance. There is always some degree of turbulence, whether from your roofline, the wake of other cars, crosswinds, etc. Turbulence destroys lift. I saw this firsthand when I changed only the roofline shape on my car and back-to-back tested them: no roof was a 250% loss in rear downforce. A fastback was a 130% gain in rear downforce. Turbulence is a HUGE factor in generating lift.
The fact is that a wing doesn’t perform the same in free-stream CFD as it does at roofline height on your car. I changed only the roofline shape and made downforce go up and down by over 400% (Cl rear .23 to 1.09). There’s probably a degree or two of change in the wing angle due to the angle of air moving over the roof, but it’s not on this order of magnitude.
So this is a very long-winded way of saying that a coefficient of lift of 1.0 is fine for rough calculations on a hardtop Miata.
If you have an open top, divide the wing’s downforce by 2.5.
With a choptop, cut it in half.
With an OEM hard top (also probably applies to a convertible with the roof up), use the figures in the table as is.
With a fastback, multiply by 1.25.
If you want to nerd out on it, you can experiment with turbulence and lift using the NACA wing calculator (change the NCrit value) and see for yourself. If you want real values, you don’t do calculations, you hire a professional to measure the real-world differences on your car.
Every racing series strives to have fair competition between dissimilar cars. The NASA Super Touring series, Gridlife, Pineview Challenge Cup, and many others use the weight of the car divided by horsepower as the primary balancing factor. Any why not? Mathematically, that seems like a good way to create parity between different cars. Well, if they were all racing in a vacuum.
In the real world, air has resistance, and overcoming resistance requires power. Drag increases at the square of the speed, so there’s about twice as much drag at 100 mph as there is at 70 mph.
Let’s take a look at two cars with identical shapes. They both have a frontal area of 20 square feet and a coefficient of drag of .48 (typical race car with windows open). The cars differ in weight, one is 1800 lbs the other is 3000 lbs.
If I input those numbers into the RSR calculator, I find out that it takes about 81 hp for the lightweight car to reach 100 mph, and about 85 hp for the heavyweight car. So weight is not a large factor here. For both cars, 60 hp is lost to drag.
Now I’ll increase the speed to 120 mph. The lightweight car needs 137 hp to reach that speed, while the heavy car needs 143 hp. For both cars, over 110 horsepower is lost to drag. If these cars were in the same class based on 12.5 lbs/hp (GLTC), the light car would have 7 hp remaining at 120 mph. The heavy car would have 97! Because these cars have the same power to weight ratio, they both accelerate at the same rate. But once they reach 120 mph, one car can barely maintain that speed, while other has power to spare.
In other words, at a faster track, you want power at the expense of weight. To illustrate that, let’s see what happens in OptimumLap when we add power, but keep the power-to-weight ratio the same. In the following table, all cars are at 20 lbs/hp. I’ll run simulations on three very different tracks, Watkins Glen, New York Safety Track, and Pineview Run. (Conveniently all within 100 miles of me.)
All cars at 20 lbs/hp, Cl -0.3, Cd .45, Cg 1.1
As you can see, the heaviest car is the fastest at every track. It’s a small difference at Pineview, and a significant 1.5 seconds at Safety Track, but a whopping 4 seconds at Watkins Glen. The simulator shows the difference in top speed is 12 mph at WGI. Wow. A difference of 4 seconds and 12 mph with cars that are supposed to be equal!
But don’t lighter cars corner faster? Not really Friction (grip) depends on weight, and the more weight, the more friction. Don’t lighter cars stop faster? Not really. A lighter car still has less grip because of less weight. The simulator factors all this in so we don’t need to.
But it’s worth noting that OptimumLap is a single-point-mass calculator. It can’t factor in elevation changes, track camber, or the fact that your car has four tires. When cornering, the outside tires are loaded more, and on a heavier car, even more. At some point you get diminishing grip from the outside tires, and so lighter cars do grip and change direction better than heavier cars. I just can’t simulate that in OL.
Another way lightweight cars are handicapped is by having to run skinnier tires. In many series, a lightweight car might be limited to a 205-width tire, while heavier cars could use 225, 245, or whatever. And what’s the logic behind that? I’m not sure. As you can see, the lightweight cars are already at a power disadvantage (anywhere outside of a vacuum), and limiting their tire width only makes it worse.
In the NASA system, not only are lighter cars penalized with narrower tires, but as cars get lighter, they take additional penalties to HP. So if your car weighs 2450 lbs, it takes a .4 lbs/hp penalty. If it weighs 2250 lbs, that’s a .5 penalty. And so on. This is completely the opposite of how it works in the simulation, because lighter cars need more power to be competitive.
Ideally, there should be a reverse corrective factor that balances the lbs/hp ratio for cars of any weight, so that lighter cars get a bit more power, and heavier cars less. Let’s take a look at what that factor could be. Ideally, you’d like to see the 1800-lb car, the 2400-lb car, and the 3000-lb car in the same second at all tracks, not 4 seconds apart.
If I do a corrective factor to figure lbs/hp like this: Lbs/(HP+((2400-Lbs)*0.016)) Then I get simulated lap times like this:
The heaviest car still wins at Watkins Glen, but it’s only a 1 second difference, not 4 seconds. At Pineview, the lightest car wins, but only by 3/10ths. And at New York Safety Track, it’s mostly a draw until the cars get heavier than 2400 lbs, but then the greatest difference is only 2/10ths instead of 1.5 seconds.
Naturally the formula could be adjusted slightly, by using a different median weight (2600 lbs instead of 2400 lbs, for example), or changing the hp factor from .016 to a lower or higher number. In any case, for a series that used lbs/hp series for classing, they can make it more fair by using such an adjustment. Of course they won’t, but data supports that they should. I mean, ideally, they’d have a different adjustment for every track….
I wrote the rules for the Pineview Challenge Cup series, and those rules also use lbs/hp as the basis. Pineview is a slower track (72 mph top speed in this simulation), so there’s much less in the deltas. One of the benefits of this series is the thin rule book, so I’m not tempted to complicate things. But if we ran our series at any other track, I would make an adjustment like this.
The reality of it is, if you race in a series that uses power-to-weight ratio as a balancing factor, you’re better off with a heavier car and more power. This often gets you into a wider tire size, as well. Adding lightness is adding slowness.
I was lucky to be able to drive a lot of other people’s cars this year.
I have Aim Solo data for most of these, as well. For each car I’ll give my quick thoughts on what I liked and didn’t like, and then go into a longer description. At the end I’ll put up a chart with lap times and other stats for comparison.
What I liked: Great torque, soft rev limiter What I didn’t like: Unsupportive seats, shift knob falls off
Pineview owns a 1998 Z3 with a hard top, which is used for rentals and instruction. It has all-season tires, which are slow but a lot of fun. The seats suck. The shift knob fell off twice, once at my feet (I found and put it back while at speed), and a lap later it went to the small of my back, where I left it as a lumbar support. The seats suck.
The Aim data shows this car has the same acceleration as my 1.6 Miata, and both cars have similar lap times on all-seasons. But the Z3 is softer everywhere, and has a lot of body roll. It’s a pity Pineview doesn’t have a spare set of wheels with good tires, because on RS4s, this car should be able to do a 1:16.
What I liked: Snug cockpit, holds 4 tires, lots of power What I didn’t like: Light switch power delivery
Napp Motorsports has a youtube channel where they test cars and build things, and in one of their episodes they got to track test Andrew Johnson’s modified BMW 128i at Pineview Run. I was there that day, and they were nice enough to let me try it.
Andrew’s modification list is long and includes swapped parts from other BMWs and the end result is a lot more power. As in 250 wheel horsepower . Andrew also added some kind of fancy diff. I don’t think it’s a Torsen or a clutch pack, but maybe some weird combination of the two. I’ve never driven a car that hooked up so immediately. I didn’t like it.
I don’t know if it was the diff or the power delivery, but this was the most difficult car I drove this year, it plowed into corners with understeer, and as soon as I got on the throttle it transitioned to massive oversteer. I like to play with throttle modulation, but this car’s power delivery is a light switch; on or off. I only did a few laps, and I had to completely change my driving style in order to get in a good lap. Stephan is a good driver, and also struggled to put in a good lap, so it wasn’t just me.
There’s a lot of potential in this car, and with a softer hit on the bottom, and maybe tuning the diff (or fuck it, an open diff), it would have been a lot faster. Maybe at other tracks it’s perfect, but at Pineview it was a handful. Weirdly, this is on the short list of cars I’d buy tomorrow. The cockpit is super nice, the seats fold down to hold four track tires, and 128s are a used car bargain.
Ford Focus RS
What I liked:4WD and lots of power What I didn’t like: Felt like FWD
Steve Wilson’s Focus RS is a good looking car with rally roots. I like virtually everything about it, except it behaves a bit too much like a FWD car. There are different modes, such as Sport, Track, and Drift, and I drove it in the Track mode.
I only did three hot laps because when I drove by Start/Finish, I noticed Steve had both of his hands up to his head, like he was freaking out that I was going to crash it. But I think he was actually taking video on his phone, and I misinterpreted the gesture. Alas, three laps is enough to get to know most cars, and I set a decent lap.
For sure the car needs more camber, and the RE71Rs were just about spent, and had already been flipped once, so that didn’t help. I’d like to spend more time in the car to figure out how to rotate it. I got it to pivot on the nose once and it felt brilliant. If Steve lets me try it again I’ll throw it in Drift mode and see if I can drive it like a rally car. Either that or put some harder tires on the rear.
Steve and I looked at the Aim data, and if we combine the parts of the track where he’s fast with where I’m fast, this car is capable of doing 15s for sure.
Honda S2000 AP2
What I liked: Honda-ness, cockpit What I didn’t like: Lack of torque
Melody and a couple friends came to Pineview to do an autocross experiment, and while we won’t be doing autocross at Pineview, we had a great time messing around in cars. I got to try Melody’s AP2, and loved it. Mostly.
I’m a Honda guy. My first motorcycle was a Honda, most of my cars have been Hondas, and I will probably have more Honda motorcycles and cars in the future. So it’s pretty hard to disappoint me in a Honda.
And yet while the car is Honda-perfect, the engine is a little disappointing. Even this longer stroke version that’s supposed to have more torque, well, doesn’t. The VTEC has a wonderful hit, but it happens so late in the game. In hindsight, I should have used 1st gear at least in the S-trap. At some other track I would be singing its praises, but not at Pineview. This car would be a predator at Watkins Glen. At Pineview, it’s prey.
Hyundai Veloster N
What I liked: Everything What I didn’t like: 19″ wheels
I drove two Veloster Ns this year, Chris Gailey’s and Philip Milligan’s. I have Aim data for both, and they are similar, but not the same. This might because of the different driving modes you can program. I don’t recall what I used in Chris’ car but in Philip’s I told him “turn everything off.”
In hindsight, I should have left rev matching on. Not that you get out of shape by downshifting a FWD car, but it’s such a cool feature and it pleasantly surprises me every time the engine blips automatically right before I throw it in the gate.
The motor is a mass of torque, and it tempts you to short shift and ride the rising boost, rather than spin it to redline. In fact I created a Veloster in OptimumLap, and it also short shifts in the computer world. So don’t rev it, ride the wave.
I’ve driven 4WD cars that felt more like a FWD car than the Veloster. I’ve driven RWD cars that felt more like a FWD car than the Veloster! Mash the throttle in the corner and of course it understeers, but if you trail brake on corner entry and transition to throttle, it’s very neutral. The power, the balance, the shifting, this is as complete of a package as I’ve driven in a FWD car.
If I was going to buy a new car tomorrow I’d buy a Veloster N. This is coming from a Miata guy who was teetering on quitting racing and buying a ND2. Yeah, the Veloster is that good. I would roll the fenders flat and fit the widest 18″ wheels and tires that would fit, add a splitter and a wing, and fucking dominate.
What I liked: Miata everything What I didn’t like: Miata power
I have two NA Miatas, my cammed NA6 and my NA8 race car. They put out about the same power and both are solid little cars. When I jump in another NA Miata, I pretty much know what to expect. Sahir’s NA Miata has Vmaxx coilovers and 225 RS4s, and I had a good idea how it would handle. Which is why I found his NA8 a bit puzzling.
It was loose. Not just in the sense that it oversteered, but it also felt disconnected, and had more roll than it should have. On the first lap I spun the rear wheels in the Toe, T9 (the uphill 180 left) and in the S-trap. On the plus side, there wasn’t a lot of power, so the oversteer was easy to manage. In fact I probably made it through the S-trap faster in his car than mine.
But my overall sense was that this was a car that wasn’t quite the sum of its parts. Maybe it needs new suspension bushings, a stiffer front bar, an alignment, or shock adjustments, I don’t know. I managed a decent lap time driving around the problems (faster than I did in the K-Miata, ahem), but when this car is sorted, it’s a PV Cup class C4 killer. Oh wait, it already won that class. Class C3 beckons.
What I liked: NB > NA What I didn’t like: NB > NA
I was lucky to drive three different NB1 Miatas this year, from Davey, Clayton, and Alyssa. NBs are better cars than NAs, and if I was building a dedicated track Miata, I’d start with a NB. I have two NAs, and it’s taken me a while (and some tears) to come around to admitting this.
Davey’s Miata has stock suspension because he also uses it for ice racing, and ice is super bumpy. Therefore, his car lacks a bit of speed and grip compared to other track-modified Miatas. But it’s really fun to drive and reminds me that a stock Miata is a wonderful thing. I forgot what lap times I ran in his car, maybe low 21s? But by the end of the season Davey was doing low 20s on well worn VR1s.
Clayton’s NB1 is a bit more modified, with some bolt on performance, Tokiko shocks, and FM dual-duty spring rates and sways. When I drove it the alignment wasn’t fully sorted out, but it felt exactly like a NB should.
Alyssa Merrill’s NB1 is the quintessential budget Miata track car. It has Delrin bushings, Blisteins, 800/500 springs, 15×9 wheels, 245 RS4 tires, a chin airdam, splitter, and 9LR wing. The motor has the usual bolt ons, but still a stock ECU.
The interior is gutted and it has a race seat bolted down, and this was my only problem with it, I couldn’t adjust the seat or heel-toe shift. This isn’t entirely why I was 1 second slower than Alyssa, but I will hang onto every excuse I’ve got. I recall I did a low 16 that day, to her low 15. Later that year she’d do a 1:14.580 and move the goal posts to the near impossible.
Alyssa’s car is also a rolling laboratory, with sensors for wheel speed, throttle, and brake, with all that going through a 5 hz GPS device tracking the usual variables. There isn’t a better track-sorted Miata that’s been to Pineview, and she hasn’t really gotten around to the motor yet. Fawk.
What I liked: It’s a Miata What I didn’t like: I wanted more from the engine and tires
Stephan Napp’s K-Miata was disappointing. It dynoed at almost 200 hp on Rick Gifford’s Land and Sea dyno (which reads like a Mustang) and on a Dynjoet this would be about 220 hp. That’s a lot of power for a Miata, and so it better have good tires. And it did: 225 Rival 1.5 S. I forgot what it’s got for suspension, maybe Xidas? It’s not lacking in any specification.
If you’d asked me before I tried this car, I would say the car should be doing 1:15s. I created a model of this car in OptimumLap and the computer says it should do a 1:15.32. And yet I could only get within 2.5 seconds of this time. What gives?
For one, I didn’t like the tires. I looked at data, and the peak Gs are great, they generated more grip than RS4s, which are my benchmark tires. But the Rival 1.5 S just doesn’t work with my driving style I guess. Alyssa or Josh might get a lot more out of the these tires, but I lacked confidence and couldn’t adjust.
I also didn’t love the engine: VTEC on top, nothing down low. Just when I got into the power I had to jump on the brakes. Like Melody’s S2000, this car might be awesome on a big track, but at Pineview, it’s a scalp for the taking. To put a point on this, both Stephan and I drove my 1.6 Miata about a second faster than we each drove his K-Miata. So this wasn’t a case of car familiarity, or lack thereof.
Stephan is boosting his K-Miata over the winter, and that’ll help the torque curve a lot. I’d like to get this back to Pineview, preferably on a different tire (I have lots, borrow mine!), and put this car into the 14s.
VVT Swapped NA Miata
What I liked: Best Miata motor ever What I didn’t like: (this space intentionally left blank)
This car started as a 1.6, got a NA8 swap, and then later a VVT swap. The head is decked, ports cleaned up, standalone ECU, custom exhaust etc. It made 135 hp on Rick’s dyno (150 Dynojet), with lots of torque down low.
This is hands-down the best Miata motor I’ve ever driven. Instant throttle response, very tractable power, and perfectly suited to the Miata chassis. I don’t think a Miata needs (or wants) more power than this. When I look at the Aim data, the VVT has the same acceleration off the corners as the K-Miata, and if these two cars were on equal tires, my money is on the VVT, despite being down 70 hp.
Unfortunately they weren’t on equal tires, Dylan was running on S.Drives. I drove that tire all last year for giggles, and it makes nice noises, slides well, but doesn’t set very good lap times. We later fit some 8-year old Z214s to Dylan’s car and he went .5 seconds faster than he did when driving Stephan’s K-Miata. Not apples to apples, but there you have it, the VVT was faster than the K-Miata with the same driver.
Stephan obviously knows the recipe for a great VVT motor, and can make another one just like it. Anyone looking for an ideal Miata motor should get in touch with Napp Motorsports and specify the same build. I hear that Dylan is boosting his car this winter, and it won’t surprise me if it goes slower around Pineview afterwards. But he’s a street guy, and I’m a track guy, and so we have different priorities.
What I liked: Flickable, planted, sorted What I didn’t like: Acceleration
When I met my wife she had a Mini Cooper S with sport suspension. It was love at first sight. So when Adam Gerken brought his Mini R50 to Pineview, I begged for a drive in it.
Adam did a lot of sensible upgrades, like later model aluminum control arms, brakes, some weight loss, and RE71Rs. I believe the motor was untouched, or at least if felt it. Yeah, slow. On the street it might feel peppy, but on the track it could hardly get out of its own way.
And that’s why it’s surprising to me how much I enjoyed it. In fact, I almost bought it! The steering is quick and precise, with a darty lively feel that people always say is like a go-kart, but I find it more like a Miata. Through the Knuckle I could lean on the power all I wanted and it was planted, without a hint of understeer. The brakes were strong, it shifted great, and the whole experience put a huge smile on my face.
For fun factor, this car was the biggest surprise for me, and I’ve been looking at R53s since (no sunroof, LSD, 20004 +).
Porsche Boxster 3.0
What I liked: Solid torque, solid chassis What I didn’t like: Care and feeding
Dieter was there for the autocross testing day and let me drive his baby. Compared to Melody’s S2000 it felt torquey, more planted, and faster everywhere except the end of the straights. I didn’t have my Aim Solo in the car, and we were running an abbreviated track with cones, so it wouldn’t have mattered anyway. But in back-to-back testing, the Boxster was faster than the S2000. I really liked the Boxster, thanks Dieter!
Used Boxsters are cheap now, but I’m not in the market. Mostly I’m worried about maintenance and consumables. Oil changes, brake parts, and the other consumables are Porsche-money, and for a guy used to buying $20 rotors and $40 brake pads, uh-uh, no way.
Scion FRS, Supercharged
What I liked: Motor, chassis What I didn’t like: Diff, shifter (v1)
Ronald Xheng has been really cool about me driving his car. I didn’t even drive other people’s cars much before this, but Ronald kept insisting I drive his, and this has led to me driving all the cars on this page. Thanks for getting the ball rolling Ron!
The first version of his car was a well tuned N/A making 190-ish hp, lots of weight reduction, good suspension bits, etc. I drove it on RS4s and it was pretty magical. People trackside could see my stupidly wide grin as I passed Start/Finish. Ron’s Aim Solo was in the car instead of mine, so I don’t have the data, but I believe I did mid 15s. There was a 14 in it, but I missed half the downshifts into 2nd.
If you pull the shifter all the way left, it gets caught in no-man’s land and won’t go in the gate for 2nd gear. Ron fixed that in V2 of his car, with an IRP shifter, which is short and buttery. He also got a clutch-style diff and a supercharger. I could take or leave the diff, and honestly the supercharger is a bit more power than I’m comfortable with, and I needed more laps, but then I broke an axle. Not my fault, this is the 3rd axle this car has broken.
Part of my lack of comfort was the Champiro SX2 tires, which I have no familiarity with. They are somewhere between a RS4 and ECS in grip, and start howling when you’re still thinking about corner entry. Lots of fun, and I could grow to like them, but I need more time, especially with the supercharger. Which is awesome. And I want one.
What I liked: Familiarity of an old shoe What I didn’t like: Speed of an old shoe
This was the first year in many years I didn’t race my brother’s Yaris. His is B-Spec prepared, handles well (if soft), but needs more power and a LSD.
I needed some FWD car data for the Pineview Cup, and so when I saw that Nick Dixon had just bought a Yaris, I asked him if we could test it at Pineview. Nick obliged, and the car came wisely shod on Conti ECS tires. I had a bunch of tires stored at Pineview, but the fenders weren’t rolled so only my 205 Toyo RRs on 15x7s fit it. For the most part the car felt like a Yaris (both good and bad), and handled better with the RRs, but it had issues.
The main problem was it kept cutting power out. I’d go through T2, ease off the brake and onto throttle, and then… nothing. It just fell flat on its face. If someone was close behind you, this is an accident waiting to happen. Nick later found out the problem was stability control, and when it engaged, you sat there for a full second while the ECU mulled things over. I’m not sure if it can be turned off or not, maybe there’s a fuse you can pull, but the car is miserable and unsafe on track with this feature on.
What I liked: Turbo, 4WD, brakes What I didn’t like: Sticky throttle, heavy, understeer
4000 pounds and a long wheelbase aren’t the recipe for going around Pineview quickly. But this Volvo wagon has the T5 turbo and 4WD, and puts the power down. It understeers a bit, and if it were my car I’d move the bias rearward with tire pressure, but The Family Truckster is fun as is.
The most disconcerting part was when I’d lift off the gas, the engine kept going! It’s only for half a second, but it makes transitioning from throttle to brakes a little weird. In a way, it’s like driving a Tesla for the first time, but you soon get used to it. By my second lap I had forgotten about this altogether and put in the necessary pause from throttle to brake.
The Firestone tires are every bit as good as people say they are, on par with Conti ECS in my book. They didn’t overheat despite the weight, and were predictable the whole session. The big Volvo also stopped really well, and overall handled better and was more fun than I thought it would be.
Here’s a summary of the cars I drove this year, with tires and lap times. I’ve included my 1.6 Miata on different tires, as a benchmark for performance.
If I didn’t have Miatas, I’d probably have a FRS/BRZ/GT86; similar philosophy, but in a coupe with better aero. My brother is thinking about a new car, and a 86 is on his list, so I thought I’d take this post out of the can and finish it. One of the reasons for owning this car would be to run it in the 86 Cup time trials, which seems like a cool series with a great rule set.
The 86 Cup rules has a Stock class, which allows you to take any modifications from an approved list. This is probably how I’d race one, but it doesn’t allow you to do much with aero. Since this is a website based on aero, let’s take a look at the aero options for the non-stock classes.
The rules allow you to modify the car, taking different amounts of points for each modification. The point total puts you into one of four different classes, which can result in different cars, with very individual builds. In the Street class, you’re allowed up to 4 points, in the Modified you get 7 points, and the Unlimited class is, well, unlimited.
Level 1 Front
Aftermarket bumper, no splitter
Level 2 Front
Splitter, spats, canards, everything
Not unless you increase track
Would help with splitter
Aftermarket or vented
Cut rear bumper
Poor man’s diffuser
Level 1 Diffuser
Starts behind rear axle
Level 2 Diffuser
Starts in front of rear axle (but how far?)
Any year OEM underbody panels
Any year OK
Any non-OEM spoiler
Level 1 wing
Up to 55″ wide, 8″ stands
Level 2 wing
Up to 57.5″ wide, 10″ stands
Level 3 wing
Anything goes, I guess
Aero options in 86 Cup
That’s a lot of options to choose from. How do I think they stack up?
The aftermarket has turned out some interesting BRZ/FRS bumpers, but without an undertray and splitter (and hood vents if you’re doing those), I’m not sure any of them are better than stock. I guess if you have .25 points lying around, then why not.
A better choice is a splitter, it costs .75 points, but then you can use any bumper you want, wheel spats, and canards as well! Data from my testing showed that a splitter is very worthwhile, and so I’d take this option with side spats and maybe canards.
If you study the YouTube videos from Kyle.Engineers, you’ll see that a diffuser doesn’t do that much unless you’re optimizing the underbody. That means first add a splitter, then side skirts, and then a flat bottom (or Venturi), and after all that, add a diffuser. Indeed, a flat bottom alone is superior to a diffuser, so I wouldn’t bother with a diffuser unless I’d done everything forward of that first, and still had points. Cutting the bumper also helps, but it’s such a negligible gain that I’d only do that if I had points to spare.
Spoilers and wings
The spoiler and wing options are interesting.
A spoiler costs zero points for OEM and .25 points for anything else. I’ve got a pretty wild imagination when it comes to spoilers, and I’d probably make my own adjustable spoiler if I was in the Street class. With more points to spend, or unlimited, I’d jump right up to Level 3 wing
There are two Level 1 wings that are whitelisted (SARD LSR and BRZ tS), and I’ve never seen the data on them. These might be a bargain, or a waste of points. From what I’ve seen, they need bigger end plates for sure.
The level 2 wing can be 2.5” wider and mounted 2″ higher than Level 1. I don’t know how much that would change the performance, but .5 points seems like a lot to spend on a couple inches.
If you need more rear downforce, Level 3 is obviously the way to go. It’s only .25 points more than a Level 2 wing, with no restrictions on width, height, or set-back distance. Go big.
A full aero package (level 2 front, hood and fender vents, level 2 diffuser, level 3 wing) is 3.5 points. That same number of points would also get you a Super 200 tire (A052, for example) on a 8.5″ wide wheel, or a built engine with forced induction.
It’s hard to say what would be the best build. On some tracks, power, on others, mechanical grip or aero. I wrote about that once before, and while some tracks favor one or the other, it would be difficult to modify your car between races. But it does appear that the 86 Cup rules strike a good balance, and it would take me a few hundred simulations to figure out which options I’d run. But at first blush the splitter and spoiler only cost 1 point, and seem like a good combo for a Street-class build.
Verus Engineering Aero Packages
Verus Engineering makes a lot of GT86 aero parts and if you dig around on their website you can find information packets, which gives you in-depth information on their aero parts. These informative packets also group some aero parts together in different “Ventus packages” that are supposed to work well together.
In a way I want to congratulate Verus on providing the customer such valuable data, but honestly… it borders on smoke and mirrors. The only thing I need is the drag and lift values, and after you wade through 29 pages of text, images, and tables, guess what they don’t give you? Drag and lift values.
It took a couple emails back and forth with their engineering department, but I finally got what I wanted. They claimed that drag and lift was confusing to most customers, so they no longer provide that. Well it’s not confusing to this customer, it’s the only two values I give a shit about.
Anyway, rant off, here’s how those Ventus Packages stack up.
Ventus 1 – This package has canards (dive planes), underbody panels over the transmission and rear suspension, and a diffuser. It’s interesting that they chose to use canards, which are very inefficient, together with underbody aero, which is totally unrelated. This would be .625 points in the 86 Cup, and have Cd = 0.372, Cl = 0.013.
Ventus 2 – This package adds a splitter and ducktail spoiler to the first package. People often think splitters and spoilers add drag, but here’s another case where you get more downforce and less drag. This would cost 1.25 points in the 86 Cup, with Cd = 0.355, Cl = -0.195.
Ventus 3 – This package adds endplates on the splitter, side splitters (side skirts), and a high-efficiency rear wing. It’s interesting that they chose to use both a spoiler and a wing on this package, I guess you’d have to take both for points. It looks like a Level 2 wing, and so this package would cost 2.25 points, plus whatever side skirts cost (not listed in the 86 Cup rules). Cd = 0.441, Cl = -0.499
Ventus 4 – This package exchanges the spoiler and high-efficiency wing for a bigger wing. Same 2.25 points as the Ventus 3 package, with Cd = 0.465, Cl = -0.633
Personally, I would not have done the packages in this way, because you’d get more benefit by going front to back. Meaning, do the splitter first, and the diffuser only after you’ve sealed up the sides and cleaned up the underbody. But Verus is trying to sell things to street-driving customers, and the splitter is not curb-friendly, and diffusers look cooler, so starting at the back makes financial sense. Likewise, canards are the last thing I’d do, but maybe the first thing a typical customer buys? Lame, but I guess it’s not what you can build, it’s what you can sell.
So you might be wondering which of those packages is fastest? Let’s run them through OptimumLap and find out. I usually factor in more drag and lift to simulate open windows, but this time I’ll use the Verus data as is. I’ve made the tire grip 1.2g across all configurations. I’ll simulate laps at Watkins Glen, NYST, and the 2010 Solo Nationals autocross track, to see what happens at different speeds.
Note that I’m a bit skeptical of Verus’s CFD values. The downforce (negative lift) is less than I’d expect. A GT86 with a splitter and a wing should be similar to my Miata with the same, which was measured at .41 drag and -1.2 coefficient of lift (with windows open, mind you). I don’t run a diffuser, flat bottom, canards, etc., and got way better values than Verus did. I don’t know why there’s this discrepancy, but anyway, I’ve added my car’s aero as the final entry in the table.
Simulated lap times based on different builds
Based on OptimumLap simulations, the Ventus packages keep going faster as you add more of their doo-dads. This holds true at autocross and medium-speed tracks like NY Safety Track. However, at Watkins Glen, notice that the bone stock configuration actually went faster than Ventus 1, and the Ventus 2 package with a spoiler instead of a wing was the overall fastest. Watkins Glen is a fast track, and if you don’t have a lot of power, drag reduction is super important. Finally, the true potential of the aero packages might be closer to my car, which flat out stomps the CFD-generated numbers. YMMV.
After reading the rules and running some simulations, this is how I’d make a car for the 86 Cup.
Street class (4 points) – Splitter (.75), vented hood (.25), spoiler (.25), 9” wheels (1.25), GT Radial SX2 245/40-17 (-1). That’s 2 points, giving me 2 points for suspension or mild engine mods.
Modified class (7 points) – Splitter (.75), vented hood (.25), level 3 wing (1.75), 9” wheels (1.25), NT01 (1.0). Thats 5 points so far, and gives me 2 points for suspension or engine stuff.
Unlimited class (any) – All the aero, supercharger, wide tires and slicks, fully adjustable suspension, etc. I mean, duh, all of it.
Stock – (0 points) – But I’d probably race in the stock class, which allows front camber plates and camber bolts, rear lower control arms, oil cooler, cat-back exhaust, base trim spoiler, and updating/backdating to any OEM parts. I’d ride on 17×8 RPF1s with 225 SX2 and call it race ready. Sell my Miatas and get into this? Tempting.
I’m pretty green when it comes to car setup, and my understanding on things like front roll couple is notsomuch. But my teammate Alyssa sent me a link to the FatCat Suspension Calculator, and after playing with the tutorial for a while, I learned a thing or two.
Bounce frequency – Lower values are comfortable, higher values less so. A 1990 Miata has a bounce frequency of 1.15 front, 1.01 rear. Fat Cat suggests that higher than 1.7 hz is not suitable for the street. That’s about 360 lbs front and 275 rear.
Roll stiffness – Determines how much body roll the car has in a corner. You can change roll stiffness with sway bars, and it won’t affect bounce frequency.
Front roll couple (FRC) – A low FRC makes a car easier to steer, but stable at speed, and susceptible to oversteer. A high FRC makes the car more stable at speed, but harder to steer, and tends to understeer. Mazda engineers felt that about 59% FRC was a good balance. Fat Cat says Miatas are biased a bit towards oversteer, and they use a higher FRC.
Front Roll Couple
Less than 58%
1990 Mazda Miata
Track and high speed setup
Front Roll Couple values
My Street Car
My street car has a Racing Beat hollow front sway bar, stock rear bar, and Tein Street Advance shocks with 7k/6 springs, which are the same shocks the calculator uses as an example. Luckily I did these all at the same time, but if I had done the shocks or sway bars individually, it would have ruined the handing.
Stock sways and shocks
RB front sway only
Tein Street Advance only
RB front, stock rear, Tein shocks
It’s easy to change FRC for better, and for worse.
Adding just the front sway bar would have made the car boring and push everywhere. Adding just the shocks, the car would have been loose mess, wanting to swap ends. But put all the parts on at the same time, and the car’s balance is very much like a stock Miata.
My Race Car
My 1994 race car is on Spec Miata suspension. When I bought it, the previous owner had disconnected the rear sway bar. That’s a front roll couple of 71.2%, which is a lot, but I didn’t know any better and anyway the car seemed to handle well like that.
But then I added a wing, which resulted in way too much understeer. This was how the car was set up during aero testing at WGI, and if you read about that, you know I also had some unfavorable negative chassis rake. All things combined, the car was an understeering pig.
Before racing at Mid Ohio last year, I reconnected the rear sway bar. This has brought the FRC back to 63.1%, which makes the car steer easier at low speed. And the wing adds progressively more rear bias, so the car transitions to understeer at high speed. The end result is a car that handles really well at all speeds. And that’s one of the cool things about aero, you tune a car so that it’s loose at low speed, and tight at high speed, just like you want it (or at least how I want it).
Getting Back 20 Points in Champcar
Champcar charges 20 points per aftermarket sway bar. I’m using a Spec Miata front sway bar. Is it worth getting 20 points back and using the stock sway bars?
Reverting the car to stock sway bars front and rear would reduce the roll stiffness by about 13%, but the FRC would be only 1.5% more. I don’t know if those changes are things I’d feel or not. However, there’s another option on stock sway bars: changing the spring rate to 850 lb front and 400 lb rear would bring the roll stiffness and FRC very close to where they are now. The only drawback is that bounce frequency would go up in this configuration, from 2.36/1.85 hz to 2.60/2.05 hz. Finally, I could leave the front spring as is, increase the rear spring to 400 lb and remove the rear sway bar, which would have the same FRC as a Spec Miata, but 9% less roll stiffness. In any case, there are a lot of options, and I can get 20 points back if I want to.
Spec Miata 750/325, 24mm/15mm sways
As above, no rear sway bar
Spec Miata, stock sway bars
Stock sway bars, 850/400# springs
No rear sway, 400# rear spring
Sway bar options on the race car
NB Miata Rear Suspension
I was reading one of Keith Tanner’s books on Miatas, and he states that NB Miatas have slightly different suspension geometry than an NA, and consequently different motion ratios. On equal springs, an NB has softer rear suspension than an NA. So if you have an NB, multiply your rear spring rate by .87 to get the equivalent to an NA spring on the FatCat calculator.
With that knowledge I ran some numbers on my team mechanic Clayton’s 1999 NB. It has 318 lb front, 233 lb rear springs, and Flyin Miata sway bars 1″ front and 5/8″ rear. The previous owner had disconnected the rear sway bar for some reason, giving a FRC of 71.4%. That’s a lot of front bias. Connecting the rear sway bar brings FRC to 58.8%, which is almost identical to a 1990 Miata. With this suspension setup, bounce frequency is just below the 1.7 hz comfort threshold, and roll stiffness is 2.4x more than a 1990 Miata. Sweet.