I previously blogged about all the reasons I wasn’t going to swap a 1.8 engine into my 1.6 Miata. I’ll sum it up with the phrase “I’m not building a better car, I’m building a better Miata.” The goal is to accentuate everything that made the 1.6 different, and more Miata, than the later 1.8s. Part 2 of this blog is my progress report. Where am I at?
- Higher compression ratio – Done. I bought a spare head on eBay so I could do all the work on the bench. I got the head decked .035″ for $50, and the engine should have about 10.3:1 compression now. I also put in Supertech +1mm oversize intake valves. I didn’t do the exhaust valves because I was trying to save a bit of money, and my understanding is the intake-to-exhaust valve diameter ratio is still good. I went with OEM valve guide seals after reading multiple cases of how much the Supertech valve seals leak. I did a simple DIY porting job, mostly just knocking down casting flash and blending. My teammate Alyssa Merrill’s landlord is a retired machinist and does heads in his spare time. He does top-notch work at a very reasonable price.
- Hotter cams – Done. Kelford 203-B cam, 264/264 degree camshafts with 9mm lift. This is a medium cam with a lumpy, but streetable idle. I’m still using stock valve springs and retainers, nothing radical. Note that there is a normally-aspirated version of this cam, which has a bit less duration on the exhaust cam. I got the forced-induction cam with an eye on the future.
- Higher redline – Done. The 1.6 has a shorter stroke, and so it’s safe to rev it a little faster. 7000 RPM on a 1.8 is the same piston speed as 7125 RPM on a 1.6. It’s easy to set it anywhere I want with the Megasquirt PNP2. I have it set to retard the timing at 7200 rpm, which is stock, and cut fuel at 7500. Also worth noting, I got a Speedy EFI variable TPS sensor.
- Lighter flywheel and clutch – Done. Fidanza 7-lb flywheel and Exedy stage 1 clutch. The flywheel feels great when rev matching, but I’m having a bit of buyer’s remorse on the clutch. It works great, I’m just thinking I should have gone for a heavier clutch in case I go forced induction in the future. This clutch is good for 145 ft-lbs, which is fine for anything normally aspirated.
- Less weight – Done. I removed the A/C (needed to be recharged and messed with my idle), and added lightness here and there. My already svelte car is down to 2100 lbs, and that’s with an OEM hard top, Hard Dog roll bar, full carpet and interior, tow hitch, and half tank of gas.
- Shorter final drive – Punt…. After a lot of number crunching and simulations, I decided to go with a 4.1. It’s an hour drive to Pineview Run, and some of it is on the interstate, and I just didn’t want the engine buzz. As a side benefit, the speedometer is now accurate. However, if I was hardcore about sticking to my principles, I would have shortened the gear ratio. If a 4.625 or 4.778 comes up at the right price, I still might do it. (Edit – I now have the 4.625 in my car thanks to Torb!)
Another place I punted on the 1.6 theme was retaining the 6-inch ring gear. These are known to fail under stock power, and only people hamstrung by STS rules actually wants one. So I swapped in a 7″ ring gear and Torsen from a later model, which required new axles and drive shaft.
I took the car to Rick Gifford for tuning. He sees a lot of Miatas and Megasquirts and has been known to work a bit of magic. He has a Land and Sea dyno (DYNOmite) mounted flush with the floor, it’s a neat drive-up experience. The dyno measures low numbers, like a Mustang in terms of power readings. I multiply by 112% to get a Dynojet number.
On Rick’s dyno, I got 129.7 hp. Power maxes out at 6800 RPM, which is only 300 RPM more than stock, so the cam didn’t make it a peaky powerband at all. The engine made 109 ft-lbs of torque at 5300 rpm, without any big dips, and a fairly flat curve. Check it out.
Apples to Apples to Oranges
Let’s compare my 1.6 build to other Miatas and engine swaps. A stock 1.6 engine would put out about out about 83 hp at the wheels on Rick’s dyno. My 130 hp is 156% more power. This is about 145 hp and 122 torque if measured on a Dynojet. Woot!
On the same day we dynoed Clayton’s NB1 with a gutted cat, Cobalt exhaust, and cold-air intake. It made 117 hp and 108 torque. That’s about 131 hp, 121 torque on a Dynojet. Of course it could be further improved with a header and standalone ECU, but even using the stock ECU, this is good power, and that’s why people swap 1.8s instead of tuning 1.6s.
But if you’re going to do a 1.8 swap, may as well use the later VVT engine for a bit more grunt. Coincidentally, right around the time I was getting my engine work done, Napp Motorsports was filming a multi-part YouTube series with their two Miatas: the first a VVT swap and the second, a K-swap. Stefan Napp also takes their cars to Rick Gifford for tuning, so this gives me a chance to do an apples-to-apples comparison.
Some background on the Napp cars. Dylan’s car started as a NA6, and, not satisfied, he did a NA8 swap with an exhintake cam. It dynoed 102 hp on Rick’s dyno, and in Dynojet terms that’s more like 114 hp. That’s not a very strong NA8, but it was choked by a 1.6 wiring harness including the AFM flapper valve. In the end, Dylan decided a VVT swap would be better.
But Stefan Napp didn’t just swap Dylan’s motor, he decked the head .040″, did some port polishing, and got a good valve job. The engine now has 11:1 compression, and exhales through a custom fabricated exhaust system. It has a standalone ECU, and on 93 pump gas it put out 135 hp and 126 ft-lbs of torque. In Dynojet numbers that’s a strong 151 hp and 141 torque. (Side note, it only made +5 hp on E98. Booo, corn.)
When you compare my 1.6 to the 1.8 VVT, the bigger motor makes 5 more hp and 17 ft-lbs more torque. The 1.6 has always been gutless in terms of torque, and right there you see it.
Stefan’s personal Miata has a K24Z3 swap, which is a 2354cc 4-cylinder used in an Acura TSX and other cars. This is the easiest way to get a Honda engine in a Miata. It initially made 175 hp on the dyno, but after further tuning, Rick managed 197 hp, and 150 torque. Wow.
|Engine||Hp / Tq||Dynojet||Hp/ Liter|
|1.6 – Stock||83 / 66||93 / 74||58.2|
|1.6 – Mine, with cams, etc.||130 / 109||145 / 122||90.7|
|NB1 – Clayton||117 / 108||131 / 1221||71.2|
|NB2 – Dylan||135 / 126||151 / 141||82.1|
|K24Z3 – Stefan||197 / 150||220 / 168||93.4|
In terms of efficiency (hp/liter), my little 1.6 kicks ass on the VVT motor, but gets beat by the Honda engine. Not that Hp/Liter is important, but it’s a good measure of the state of tune. Dylan is planning future mods to hit the elusive 100 hp/liter, so his 1.8 may yet surpass my 1.6.
Where’s the power come from? What did it cost?
I have a spreadsheet where I’ve entered data from various dyno charts I’ve found on the web. By looking at the parts that were used and the total output, I can make a fair guess at which parts produce how much power. Based on that data, this is what made what, and how much it costs.
|DIY cowl intake||5%||105%||$40|
|Cams, cam gears||15%||135%||$700|
|+1 mm intake valves + seals, valve job||4%||139%||$500|
|DIY port and polish||2%||141%||$0|
|.035″ head shave||6%||147%||$50|
By running a standalone ECU (MS PNP2), I was able to get rid of the restrictive flapper valve (AFM). This is really the first thing anyone should do to a 1.6, and it makes all the other mods tunable. But it’s not cheap, and when you add in $600 for dyno tuning, this comes to nearly $100 per 1% power. That’s my ceiling for my “worth it” calculation, and I like to be closer to $50 per 1% (or $50 per hp, if you think that way). But the ECU makes all the other things better, so you have to start there.
The cams added about the same amount of power as the ECU, and were a big bang for the buck. I probably didn’t need the adjustable cam gears, but I decked the head and thought it was a good idea to get the cam timing back to stock. I still haven’t played with the cam timing, so there’s probably a bit more power there.
Keep in mind that these individual power gains are all guesstimates, I certainly wasn’t going to dyno and tune each part as I put it on. In all I spent roughly $3300 to get 56% more power. That’s $63-70 per hp, depending on the dyno.
As you can see, modifying a 1.6 engine isn’t the best use of money, but almost nothing car related is. Common wisdom is to just drop in a VVT and be done with it. I can’t argue with that, especially after driving Dylan’s car (future blog post). But if you have a low-milage 1.6 and feel like it’s dumb to swap a perfectly good motor, or if you just want to buck the motor-swap trend, then tuning a 1.6 can be pretty rewarding.
I feel like the project has been a total success. I’ve improved everything that made the early cars better Miatas. In terms of power to weight ratio, the car is about 16.1 lbs/hp, with me in it. That’s about the same as a new ND2 Miata, and in that light, a downright bargain.
But it’s no rocket ship. When I hit a long straightaway, I’m still patting the center console giving her the giddy-up: “C’mon baby, let’s GO!” An underpowered is still part of the Miata charm, after all.
I got to track test both of the Napp Motorsports Miatas back to back to back with my NA6. I’ll report on that after their video comes out.