Classing Miatas for SCCA Enduro Nationals

Sports Car Club of America (SCCA) has finally gotten into the budget endurance racing game. They are late to the party; 24 Hours of Lemons, American Endurance Racing (AER), Champcar Endurance Series, Lucky Dog Racing (also in Canada), NASA TREC, World Racing League (WRL) and others have been partying in this space for a while.

My brother and I are working on a blog post that compares SCCA Enduro Nationals to all of the other endurance racing organizations, and we’ll publish that on You Suck at Racing sometime in the near future. But I wanted to specifically talk about Miatas, and where they fit into SCCA’s new enduro ruleset.

Classing Rules

The SCCA classing rules are based on your car engine’s displacement, which determines its initial class, fuel capacity, tire width, and race weight. There are four classes, E1 to E4:

	E1	E2	E3	E4
Displacement (liters)	6.2	4.5	2.9	1.9
Fuel (gallons)	20	17	15	14
Tire (width )	295	255	245	225

Your car takes additional modifiers to its displacement for the following:

• Drivetrain – A turbo doubles your displacement, and there are other minor modifiers for transmissions, etc. However, engine swaps and tuning is free.
• Weight – Car weight may adjust the figured displacement up or down .5 liters. If your car is unusually heavy, it will get more displacement; if it’s too light, it gets less.
• Suspension – Adjustable suspension, either valving or height, adds .5 liters displacement. If you have modified suspension pickup points, add 1 liter. I guess that means you take 1.5 liters if you have both, ouch.
• Aero – A splitter or wing adds .25 liters displacement each. Aero is a somewhat grey area, I go into that in more detail.

There’s a Microsoft Excel spreadsheet/calculator to make things easier (download), but you should probably also read the full PDF. The rules are really quite simple once you wrap your head around the fact that it all revolves around displacement. I’ll go into some more details on these, as it relates to Miatas.

Engine

Engine tuning is unlimited, which means a Spec Miata with a stock 1.8 engine is classed the same as a hot-rodded NB2 with cams and ITBs putting out 180 hp. Likewise, engine swaps are open. The rationale is because a more powerful engine burns more fuel, which requires more pit stops, and since fuel tank size is limited, this should make the cars even on speed over the course of a 6-8 hour race. Ahem. If you say so.

Turbos double the displacement, so a 1.4 Fiata is evaluated at 2.8 liters, a 1.6 turbo becomes a 3.2 liter engine, and a Mazdaspeed Miata is 3.6 liters.

Rotary engines are a 250% modifier. Thus, a 1.3 liter RX8 comes in at 3.25 liters and 3250 lbs. That’s a bit unjust for the 238 hp the engine puts out. I would have used the same modifier for both turbo and rotary, which would make the 1.3 into a 2.6, and a race weight of 2600 lbs, which is a lot more realistic than 3250 lbs.

For a Miata, the smart money is on the highest output, lowest displacement, normally aspirated, non-rotary engine you can swap in.

Weight

A car’s minimum weight (which is with a full fuel tank but without the driver) is based on the engine displacement, plus any drivetrain modifications at a rate of 1 lb./cc. In other words, if you have a 2.5 liter car, your race weight is 2500 lbs. There’s a minimum weight cap at 2,000 lbs, so all OE-engine Miatas (1600cc to 2000cc) are going to start at one ton.

Most Miata endurance racers are heavier than 2000 lbs, and so you’ll get some points back for being over the weight limit. You get .1 liter back, for every 50 lbs over the weight, to a maximum of .5 liters. For example, if your Miata weighs 2200 lbs (full tank, no driver), you’ll get .1 liter per 50 lbs, or a total of .4 liters back. Your 1.8 Miata is now a 1.4 liter Miata.

Aerodynamics

Aero also adds to your displacement, you must add .25 liters for a splitter or a wing (each). If you read further into the aero sections, there are some grey areas and unknowns. Section 3 states “The following aerodynamic modifications may be subject to modifiers in the class table” and then lists definitions for airdam, splitter, and wing. Let’s take a look at Section 3 in more detail:

a. Front Air Dam/Spoiler

An air dam is defined as such:

• i. Shall be mounted to the body and may not protrude more than the thickness of the material (0.5” limit) beyond the overall outline of the body when viewed from above, perpendicular to the ground, or aft of the forward most part of the front fender opening.
• ii. Openings are permitted for the purposes of ducting air to the brakes, cooler(s) and radiator(s).
• iii. An undertray may be added. The undertray may close out the area from the leading edge of the bodywork (including the spoiler/air dam) back to the forward most part of the front fender wheel opening.

I understand what an airdam is, what I don’t understand is why they bother to define it? I can’t find a displacement modifier anywhere in the rules or the Excel calculator, which leads me to believe airdams are free. But if that’s the case, why dedicate a section to it and say that airdams “may be subject to modifiers in the class table”?

Many racing rules allow for some variance in angle of the airdam, but SCCA Enduro rules do not. You can’t use your 4.5-degree NASA-legal 9 Lives Racing angled airdam in the SCCA Enduro Nationals.

b. Splitter

The splitter rules seem pretty straightforward, and apparently allow “underbite” style splitters for free.

• i. A splitter (horizontal, single plane aerodynamic device attached to the lower front of the vehicle, protruding forward) may be added to divert air and produce downforce through vertical pressure differential.
• ii. Splitters shall have no vertical deviations and may protrude three (3) inches from the forward points of the front bumper, and be no wider than the outside edge of the front wheels when pointed straight.

Note that a splitter is defined slightly differently in the general rules, but you have to dig to find it. Within section 1.1, Classes; sub-section C, National Class Table; sub-sub-section 5, Adjustments; sub-sub-sub-section C, Aerodynamic: “Front splitter extending beyond the front bumper as viewed from above: Add 0.25L.” If I’m reading this correctly, then this picture below is not a splitter.

c. Rear Wings

Wings are limited to a single-element, 720 square inches. Wings must be completely contained between the rear axle center line, the sides of the vehicle and rear‐most point of the rear bumper as viewed from above. The height of a the wing varies by body type. On a Miata, the wing may not be higher than windshield or hardtop, whichever is higher.

Missing aero???

The intention of the rules is to allow people to build the cars they want, but by not mentioning various popular aero items, it’s confusing. Are they free or are they outright illegal? Where do the following items go?

• Spoiler – A spoiler and a wing are not the same thing. Is a spoiler free, or does it count as a rear wing?
• Canards and vortex generators – Mostly worthless, but some people use them. If your car has them, what happens?
• Underbody – Side skirts, flat bottom, diffuser… are they illegal? If they are legal, is there a maximum size?

Classing Miatas

OK, now that you know the basics of the rules (and gaps in them), let’s class some Miatas.

Because the E3 and E4 classes have a maximum displacement that ends in .9 (1.9 liters and 2.9 liters), and because coilovers and aero are each .5 liters, you’ll see that a that an engine that is a multiple of .5 liters gets screwed (1.5, 2.0, 2.5). It’s better to have an engine with 1.4, 1.9, or 2.4 liters.

1.8 Spec Miata – Class E4

Your average 1.8 Spec Miata weighs about 2200 without the driver. The SCCA Enduro rules have a minimum 2000 lb weight, which means the car is 200 lbs overweight, and so it gets some displacement back. The formula for that is .1 liter for every 50 lbs, and so you get back .4 liters of displacement (2200 lb car – 2000 lb displacement min weight). The car is now evaluated at 1.4 liters (1.8 original – .4 for weight).

You also have to figure in the displacement modifier for shocks. Spec Miata shocks are height adjustable, and so they add .5 liters of displacement. Add that up, 1.4 liters + .5 liters = 1.9 liters. A 1.8 Spec Miata makes it into Class E4 like it was meant for it. (As long as it weighs 2200 lbs or more.)

1.6 Miata with a wing- Class E4

If you start with a 1.6 Miata, you can add a wing. Let’s start the car at 2250 lbs. This could mean adding ballast, but you’re allowed up to 250 lbs, of which only part of that would be necessary. At 2250 lbs, you’d get back the maximum displacement of .5 liters, which brings the car down to 1.1 liters of displacement (1.6 – .5 = 1.1). Now add coilovers (.5) and a wing or splitter (.25) and you’re at 1.85 liters. Personally, I’d take a wing over a splitter. But if spoilers are free, then that might sway things towards a splitter and a spoiler, rather than a wing. The only way you can use coilovers, a wing, and a splitter on a 1.6 Miata is by using non-adjustable shocks, and if you’re going to do that, start with a 1.8.

Aero 1.8 – Class E4

I’m a sucker for aero. If I was going to enter my NA8 endurance racer in the E4 class, I’d fit non-adjustable shocks so I could go all in with aero and use a splitter and wing. I think aero is worth more than the Spec Miata suspension I have on my car right now, maybe if I had Xidas I’d feel differently? I’d get the car to weight in at 2200 lbs, which would get back .4 liters of displacement. To this I’d add the aero, putting the car at 1.9 liters of displacement, right at the class limit.

Unfortunately I wouldn’t be able to use my fastback: “Aftermarket hardtops are permitted, but may not change the aerodynamic profile of the vehicle.” Every other endurance racing series allows fastbacks. Maybe I won’t race with these guys after all.

NC – Class E4 or E3

• E4 – NC Miatas are 2 liters, and thus 2000 lbs, but are probably going to weigh more than 2250 lbs, and so they’d come in at 1.5 liters adjusted for weight. No NC will be on adjustable shocks, because that would put it over 1.9 liters, but one could use a splitter or a wing.
• E3 – Class E3 cuts off at 2.9 liters, and so a NC could use coilovers and either a splitter or a wing, but not both. This is not a very compelling car.

NC with 2.5 swap – E3 or E2

• E3 – The class is based on 2.9 liters, and so a NC with a 2.5 swap starts at 2500 lbs and can’t use coilovers unless it adds weight. Using the standard formula means you have to add 50 lbs. So, 2550 lbs (without driver) and 190 hp-ish without aero. That’s OK, but there are better options.
• E2 – If you put aero and coilovers on it, you could run it in E2. This would be 3.5 liters, and you could then remove 250 lbs to get the maximum benefit (car weighs 2250 lbs) and be at 4.0 liters. This is under the 4.5 liter ceiling, and underperforming in that class.

ND – Class E4 or E3

• E4 – NDs also start at 2 liters and the same 2000 lbs, but if you pared one down to 2050 lbs, it would come in at exactly 1.9 liters adjusted displacement. That’s a car without aero or adjustable suspension, but at that weight, it could be a hugely fun car to drive. At 2125 lb lbs, you could add either a wing or a splitter, but no ND in class E4 can use adjustable suspension, or both a wing and splitter, as that would be over 1.9 liters.
• E3 – Class E3 cuts off at 2.9 liters, and so ND Miatas can use coilovers and one aero item, but can’t use both a wing and splitter.

K24 Miata – Class E3 or E2

• E3 – A much better swap than a 2.5 is .1 liters less, for 2.4, it just fits the classing formula better. If you have a 2.4 liter K-swapped Miata, your minimum weight is 2400 lbs, which would put you into the E3 class right away (meaning a larger 15 gallon fuel tank and 245 tires). The E3 class is capped a 2.9 liters, and so you’d have .5 liters of displacement to “spend”. Likely choices would be coilovers or aero, but you can’t take both.
• E2 – You could also add the full aero kit to coilovers and go into the E2 class. In this case you have .5 liters to spend on weight reduction, and the car could weigh 2150 lbs. That’s a car that sounds like a lot of fun, but it’s .6 liters under the displacement limit.

Turbo 1.6 Miata – Class E2

Forced induction doubles the displacement, and so this would put the car at 3.2 liters, way under the weight value of 3200 lbs (recall that race weight is the same as displacement CCs). That means you’d have to take .5 liters for a weight penalty, bringing the car up to 3.7 liters. Add coilovers and a wing and the car is at 4.45 liters, just barely making it into class E2, which tops out at 4.5 liters. That means you can’t use both a wing and a splitter, you have to choose. Or use a splitter and spoiler, if the spoiler is free. But is it?

Turbo 1.8 Miata – Class E2 or E1

• E2 – Displacement doubled puts the car at 3.6 liters, and at the 3300 lb max weight limit. Add in the .5 liters for being grossly underweight, and you’re at 4.1 liters. This doesn’t leave you with enough points for coilovers, but you can choose a splitter or a wing. Compared to the normally aspirated builds, this one’s a loser.
• E1 – A particularly bad option is to put a full aero car with coilovers into E1. Your car would be at 5.1 liters with coilovers and aero, a full 1.1 liters under the class limit, with nowhere to go. You get 20 gallon fuel tank (where would you put it?) and 295 tires. Good luck with that.

Conclusions

The SCCA Enduro Nationals rules aren’t finalized yet, and things like maximum stint time and minimum pit stop time are as yet undefined. They are missing some aero definitions as well. The first race is in March, and teams need to prepare, so I hope they finalize this soon.

While the classing system is untested, it looks fair (at least within each class), and the rules are at least easier to understand than the SCCA autocross rules (370 pages) or the SCCA road racing rules (1000 pages). Of course all rules need some adjusting after a season, but these seem like an OK start. As an avid endurance racer, it’s great to see more options.

As it goes for Miatas, NA/NB cars have some interesting options in E4. NC Miatas are not particularly good choices. An ND with aero and shocks looks like it would be a solid contender in E3.

Personally, I wished the SCCA allowed convertibles with altered rooflines (fastbacks, shooting brakes, etc) like every other endurance racing series does (as do sprint racing series like GLTC, NASA ST/TT, EMRA, etc.). I could throw my street hardtop on my racecar, and fit non-adjustable suspension, but since I’m already racing in other series, why would I change my car fit into the SCCA’s rulebook? The answer is, I wouldn’t.