Building a NASA ST6 Track Car: From Miata Racing to a New Budget-Friendly Race Build

So… the Background. What and Why?

I've been racing Miatas in some capacity since 2006. Ive owned/built/driven/raced all kinds of miatas; windshield-less EP/FP stuff, NASA PTE, PTD, Supermiata S1 and S2, K24 swapped ST5, ST4 and Gridlife GLTC.

I listed my previous K24z3 swapped NB miata racecar for sale about a year ago to this date. It sold In January this year, 2025. I spent all of 2025 off the big racetrack and just autocrossed. The itch has returned.

I played with my BRZ in NASA TT5 and HPDEs for a few years but while that chassis is really good, it has always felt like a compromise in too many ways. Whether that is the parts bin nature of the chassis, the FA20 itself, my choice(s) to make it and keep it a dedicated now-DST autocross specialist, who knows. It also slots into the same class level as my previous car did(NASA ST4-5 and GLTC-ish.)

An 86 prepped to a high level in SCCA DST autocross does cross over to NASA TT5 or Gridlife Club TR, but is an also-ran midpacker there. To run at the front of those classes requires large and expensive mods that eliminate it from DST legality. Then add the safety gear investment required to w2w one in either ST5 or GLTC.

I know what a car of that pace/prep drives like, I also know what it costs to run long term and also again what it costs to compete at the front in those levels of classes. I dont want to keep spending that way.

A New Direction

I am in the fortunate position to be able to move the intended cost/budget of "upconverting" my DST BRZ to ST5 or GLTC and allocate it to a new separate car. That does put a pretty modest budget cap on this project, but its somewhere between a LeMons car and a mid pack SpecMiata-from-scratch budget.

This hobby is also a social activity and I have more local buddies playing in TT6 and ST6 than I do in ST4/5 and GLTC. (Since starting this build Gridlife has announced the 2026 schedule which essentially totally removes them from my participation consideration.)

For a mix of those budget and social group reasons, I want to build a new to me NASA ST6 car, that isn't a Miata.

Choosing a Platform (The Right Way)

Picking a car AFTER you've picked the sanctioning body and class is a very fun/interesting theorycraft. Designing the build of that car from scratch with no sunk cost in sentimental parts/mods/etc is yet another very fun theorycraft.

NASA's ST5 and especially ST6 have lots of rules intended as cost containment. However, the overall theme of Super Touring is very open, lots of flexibility. It is also mature, with decades(back to Performance Touring) of data/history and parity. It is also extremely stable compared to the current darling of sprint racing, Gridlife GLTC, again DECADES of this P:W maths and balancing various chassis/engines.

Its extremely comparable to Forza Motorsport's PI system, for the fellow gamers.

The Rules That Shape the Build

The rules:
https://members.drivenasa.com/rules

The ST5/6 rule:
https://nasa-assets.s3.amazonaws.com/document/document/24000/2025_ST_5-6_Rules.pdf

The Class calculator tool:
https://form.jotform.com/drivenasa/st-tt-car-classification-form

Right off the top, the biggest cost containment/scope creep prevention is the class maximum horsepower rule.

"ST6 RWD and AWD models must have 168 (one-hundred sixty-eight) and FWD models must have 174 (one hundred seventy-four) or less factory rated engine horsepower and an engine displacement less than 2449 mL (cc)**, unless they are listed as eligible models in Appendix C. Forced induction is not permitted in ST6. 2006+ Mazda MX-5 models are specifically not eligible for ST6."

Next is the engine swap rule:

3) Engine and head swaps are permitted, but the donor vehicle must be a model eligible to compete in ST5 for an ST5 vehicle, and ST6 for an ST6 vehicle

An added complication is the clarification about cool JDM stuff, and therefore JDM-only engine swaps:

Vehicles must be "approved for street use by the U.S. D.O.T. (Non USDM vehicles may be approved by the National ST Director on a case-by-case basis)"

Narrowing Down the Options

That narrows the starting chassis list pretty quickly.

The Appendix C has some particular outliers that get allowed back in. I originally wanted to start here so as to minimize the amount of minimum work needed to hit the class max P:W.

Appendix C – Additional ST6 Eligible Vehicle Models

• Acura Integra GS-R (’94-’01) (1.8L, 170hp)
• BMW E30 325 (’87-’91) (2494cc)
• Ford Focus SVT (’02-’04) (2.0L, 170hp)
• Nissan Altima Sedan (‘02-’06) (2.5L, 175hp)
• Nissan Altima Sedan/Coupe (‘07-’12) (2.5L, 175hp)
• Nissan Sentra SE-R (’02-’06) (2489cc)
• Nissan Sentra SE-R Spec V (’02-’06)(2489cc)
• Porsche 924 S (’87-’88) (2479cc, 8 valve)
• Porsche 944 (’83-’88) (2479cc, 8 valve)
• Porsche 944 (’89) (2688cc)
• Subaru Impreza RS (’98-’01) (2457cc) (AWD)
• Subaru Impreza 2.5i (’08-’11)(2457cc) (AWD)
• Toyota Corolla XRS ('03-'08) (1796cc, 170 hp)
• Volkswagen Jetta ('06-'07) (2480cc, 150 hp)
• Volkswagen Rabbit ('06-'07) (2480cc, 150 hp)

What Didn’t Make the Cut

I investigated both the SE-R SpecV and VW 2.5 Rabbit options pretty heavily. There is a really attractive sweetspot with Nissan Contingency and that SpecV with the OEM 6spd trans, OEM LSD diff and OEM optional Brembos makes a very quick and easy class-max TT5 missile car, but the aftermarket support means its got too many weird custom problems to solve.

I then moved onto a GSR sedan, or just GSR swapping any DC2 roller, but have yall looked at vtec honda B series prices lately?!

How We Got Here

In investigating that Integra path, I had a local deal fall into my lap, which is how we got here...