Not a miata, but this forum is home for me. I also need a sort of journal space if i want to move this content elsewhere.


So.. the background. What and why?
To be as short as possible, Miatas got boring. 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 thats 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 ST5 and GLTC-ish.)
An 86 prepped to a high level in SCCA DST autocross does cross over to NASA TT5 or Gridlife ClubTR, 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.

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 4/5 and GLTC. (Since starting this build Gridlife has announced the 2026 schedule which essentially totally removes them from participation consideration.)
For a mix of those budget and social group reasons, I want to build a new to me NASA ST6 car, that isnt a Miata.


Picking a car AFTER youve 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: https://members.drivenasa.com/rules
The ST5/6 rule: https://nasa-assets.s3.amazonaws.com..._5-6_Rules.pdf
The Class calculator tool: https://form.jotform.com/drivenasa/s...ification-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

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 The following vehicles are approved to compete in ST6 despite either an OEM HP or engine displacement greater than the listed maximum in Section 4. ....
Engines from these vehicles may only be used as a swap donor to ST6 eligible vehicles of the same model of a different year.
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)

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 TT6 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?!
In investigating that Integra path, I had a local deal fall into my lap, which is how we got here...



While this sanctioning body and this specific class are not new to me, the car, brand, and even general drivetrain layout ARE new for me.
I've won championships in this club/preceding ruleset(NASA Super Touring was Performance Touring when I won mine) but ive literally never raced a FWD car on pavement. I rallycrossed a mk3 jetta over twenty years ago...

 

So I am a Honda boi now.











This car is an old Honda Challenge survivor. It last raced in 2012.
It has a rear disc upgrade already, and has an oversized 1.75" but minimal attachment point cage, intended to cover it for budget endurance racing as well as sprint racing. That cage never got painted...
It cam with a pile of spares, spindles, calipers, bumpers, a second hatch with a lexan window, pads, two pairs of wheels, etc.
It last(only?) ever had a D series engine. I understand that there was some partial prep to bring it back out with a B series somewhere around 2015 but that effort stalled and fizzled.
The purchase deal came with some B swap related parts, including an Integra B18 LS transmission, B18 header/exhaust, parts of an engine mount and shifter swap setup. Not a complete swap kit, but enough "free" parts that I was initially fully sold on a B swap.
Everything moved into my own shop:



More background/decision making before I start the heavy photo journey...

Remember when I asked "have yall looked at vtec honda B series prices lately?!"?
Budget very quickly ruled out a proper, sexy, fun B16 engine or even a grey area B16/18b "poor mans type r". The rules prevent a hot B18c type R or even a GSR swap, as the GSR motor has to stay in a dc chassis Integra due to appendix C, above.
Similar to the GSR b18c, the B20 CR-V motors have a key rulebook disallowance, in this case regarding the transmission. My EF Civic is legally allowed to receive a B20 CRV motor, but I must use a transmission that matches the host car or the donor car. The CRV never shipped with a 2wd manual transmission, the manuals are all 4wd. I am not allowed to put a CRV engine next to a a DA Integra transmission in an EF Civic. That engine/trans pair must go into a host car that came stock with a B series manual transmission, like a DA Integra or EK civic. The EG civic would be in the same position as my EF.

So I am allowed and can afford an Integra B17 or B18b because I need to also use their matching B series transmission.

I bought a sight unseen B18b1 before i even brought the chassis home, but it turned out to have a spun bearing and a very, very blue crank journal. Fortunately that seller and I agreed on a 50% refund, so I now own a potentially rebuildable core block/crank, and full b18b1 cyl head. If anybody wants it...






I poked around for almost a month trying to source a second known-good B18b1 swap...

 

"You sold your Honda K swapped racecar to build... another Honda K swapped racecar?"
Turns out, yea.

The K series engine family needs no introduction, but I had to do even more reeducation to get one into this low power class.
We have the transmission hurdle to jump, not just the horsepower limits to play in.
Additionally, the EF hood line makes K24s pretty difficult. Let's get the k24 discussion out of the way...

The max power rule doesnt allow any "high compression" or dual-vtec K24 engines. Period. These would be the fun/sexy jdm K24a and jdm/usdm k24a2. Also not allowed are the high comp k24z motors, z2, z3, z6 and z7.
The only K24s allowed are the low compression "Eco" variants: K24a1, a4, a8, and z1. The z1 never came with a manual transmission, so its out. The K24a1/4/8 would also require using the Accord's 5 spd box. Not the end of the world, just have to find a whole driveline donor and deal with the height of the 24.

The K20 family is similar story. The fun ones are illegal, and the allowed list is even smaller, but it would fit better.
High comp K20a and a2 straight up not allowed. Low comp "Eco" K20a, a1, a4, 6/7/9 would need a JDM/EUDM donor allowance on case by case basis.
High comp k20z1/3/4/5 variants, not allowed. Sole outlier is a Canadian/EUDM k20z2 that would need a series director allowance.
That leaves the extremely well renowned base model USDM RSX and 01-05 Civic Si K20A3.
The other reality of K swapping an EF civic is that you need/use several RSX or EP3 civic Si parts; the shifter, shifter mounting box, shifter cables, both axles, the intermediate shaft and the ECU, engine harness, etc...

Done. Decision made. I am K20a3 swapping a 1988 Civic to replace my K24z3 swapped 1999 Miata. What a time to be alive.

What is the easiest way to source a known-good 20 year old engine, transmission, and all associated swap parts?
It is NOT to drive 3 hours for a $200 longblock.











So I find myself the owner of a potentially rebuildable core K20a3.

 

This is great so far. Thanks for sharing here! Most of us that love miatas also respect old Honda's for the same reason, I always thought a fwd build would be fun on track, though I've never driven one in that capacity. I miss my old DC2 Integra.

 

GLTC sub-200 meta build when?

 

Im excited for the change of pace and to finally say i race gods chariot golden era honda.

With Pitt gone and the closest event being the biggest festival at Gingerman, the chances of that happening are very slim.
The K can be potent, and im allowed to do some pretty funny "Vtec Killer" internal mods that make k20a3 a non-vtec 200whp oddball that is still technically legal in 6. The reality is that GLTC is best crossed into from ST4 because of ABS and aero reasons. Even ST5 cars dont really work in GLTC.
Check back in 2027 when they write yet another parity breaking and meta changing ruleset to move gltc down to maybe 14:1 haha.

 

My shop space doesnt have a hose bib, so I swung by the house on the way home to wash the roller while it was still strapped to the trailer.







No brake lines, master, and no handbrake due to the rear disc conversion was a fun loading/unloading experience.

At the shop I leaf blew out the interior, spent an afternoon de-stickering and got it rolled in. First real look at the thing in solid daylight and with all the doors/hatch open. Great value for the investment so far, but man, the To Do list is looooong












The 15x9 Rota Grids with 225/45/15 Toyo RR on the front are leftover from my KMiata. They may very well end up on the car in a reverse-staggered setup like pictured, but are not my first intention,

The exterior is actually in good enough condition to either leave alone or leave at the bottom of the To Do list.
I ordered some amber corners and bumper lights and thats it. Maybe hood pins later on so i can delete the cable and latch.
The blue fenders are both pretty beat up, enough so that the drivers side corner light doesnt sit square/properly once screwed in tight. I will play with bending that bucket back into alignment, but I have a more straight pair of black fenders...

The interior is the bigger project:
Cage needs scuffed and painted.
Window net mounting needs updated/upgraded. I'll go to a wrap-around lower and cut off the existing alloy flat stock lower mount ASAP. I may buy a new spring-pin upper bar as well.
Dash and chassis harnesses can be removed, as im moving off the 36 year old wiring altogether; engine(partial ECU connection), charge/start, dash(partial ECU connection), body(fuel pump), etc.
Cage padding has to come off for paint
Some remnants of sound deadening to get out from the steering column area.
Holes. Holes. Holes.
Maybe swap the rear hatch if I decide to paint/wrap the exterior.

 

Mocked up the old spare seat with a Miata works bell hub and the wheel from my BRZ
No the miata and civic dont share a hub spline, but the miata hub fits over the smaller civic shaft for mockup.


So much room in here compared to a miata.



The first real work session was primarily to get the harness out and panels off to prep for (cleaning)paint.










This is where it sits today: The Jongbloed 15x9s that came with the car are now in use as roller with some old 245/40/15 rt660 GLTC scrubs I have laying around.
I was able to file down the casting ridge off the front knuckles and delete the 5mm spacer that was on the front behind the Rota Grids in previous photos. The 245/9" setup will still need a lot of fender work, and I cant really do much until I have the car near comp weight, post swap and with the incoming PCI upper arms swapped in.



Lastly, for a bit of thanksgiving week motivation, I rolled the 'rebuildable core k20a3' under the car for a preview expereince:

 

That is a minimalist cage. My brain wouldn't let me move forward without some additional bars and/or gussets.

 

I agree with the mindset, and footwell intrusion bars are on my list, but I draw the line there. My Kmiata was much like this; no roof diag and no rear leg diag, but did have footwell intrusion bars. If I was building a heavier or faster car for ST4 or GLTC, it would get an FIA bar and a roof diag, and probably attach to front shock towers.

This car is from the era when cage attachment points were seen as a performance benefit and either tightly controlled(min of 6, max of 8) or simply illegal(doorsill and A or B pillar attachment in PT)
It is minimalist in bar count, but upsized in diameter for enduro racing GCRs(1.75") so I do have that piece of mind.

I am hoping that whatever local welder buddy I can con into doing/helping/teaching with my engine mount bracket can help me with footwell intrusion.
If I end up buying a multiprocess welder I am delusional enough to think I can do the motor mount as practice and maybe do footwell bars and backing plates myself.



EDIT: I actually found a pretty easy DiY solution.
https://www.summitracing.com/parts/sum-770970
https://www.summitracing.com/parts/aaf-all22678

 

This is very exciting. I love me an old Honda as much as NAs and NBs. Godspeed brother.

 

Good luck with the project!

Most of us pick the car with our hearts, and just run with it - I did. Picking a car for a particular class/budget/etc is the smarter way, and will probably yield better results. The middle ground is to pick the car, then find the class/racing that best suits it and the other constraints of budget/access/etc. For us running cars we bought because we love them, and love modifying them, the task is avoiding the 'over-modified' problem where the only classes we are eligible for we are uncompetitive. As a walking example, I have unusable aero sitting in the workshop because my chosen class mandates nil non-factory aero. Ooops!

 

The plates could probably bought from send-cut-send for cheaper. If you don't have access to CAD, send me a message and I'll draw something up for you to use.

 

As a somewhat experienced “k-swapped golden era Honda” racer…I wish you nothing but luck and good fortune with axles!

 

Sub'd. Great read as always. We've got a small team in SoCal whose drivers take turns fielding a TT3 Mustang and a TT6 EF. I just saw the main guy at the track last weekend and he picked up another EF that they were doing some shakedown on. Should've asked 'em more about the car.

Love the shell and your plans for it. It'll be cool watching to see what you find to be the TT6 meta. We've got a solid TT6 showing out here but the class is mostly recreational and I don't think anyone has built something to the absolute limit of the ruleset

 

Thanks yall. I'm excited for the newness of it all. If it turns out like the Kmiata did and the some of the parts is less than I hype it up as before I experience it, then i'll probably build a fresh Supermiata S2 for 2027 and drive it in HPDE by myself lol.



Ironically, the fastest xT6 car, i think, is still a Spec944 with hoosiers bolted on. My hope is that the FWD credit can offset the Aarm penalty and I can replicate that kind of pace. The ruleset has moved from 18:1 up to 19:1 since, but the 1:39s at Mid O pro were run by four different cars in 2019, including a DA integra, two NB miatas and such a 944 double dipper.
That is my rough goal: A perfect weather sub 40 at Mid O in the current 19:1 ruleset.

 

In all my research for this swap, there were some key learnings about FWD k swaps that are different from the RWD kswap i did a few years ago.
I don't already have the intended Miata transmission, shifter.
I can use stock engine harnesses of a couple different Honda varieties, I am not locked into a aftermarket third party or a custom cut and spliced adaptation.
The reality of OEM ECU hardware is that all the Kswaps of this era also desire the 02-04 RSX ECU for Hondata. The 05-06 RSX ECU and/or immobilizer are tricky(extra cost) to reflash/chip.
The motor I want comes in two different cars here in the US, the base model RSX and the "EP3" Civic Si from 2001-2005. That civic has the famous dashboard mounted shifter, so the swaps all require the more normally-located RSX shifter box, cables, etc.
The reality of my ruleset is that I need the apparently very rare 5spd transmission from these same two cars. There are plentiful 6spd options(that I am not allowed to use) on every street corner, but the 5spd is shockingly rare. Guess what percentage of base model RSXs were automatic?

Instead of trying to piece together the engine from one of two sources, the shifter, cables and ecu from a known single source, the transmission which turned out to be very hard to find, and then every random nut and bolt needed to put it together but not included by any of the 30 unique ebay resellers I would have to transact with...

I bought a donor car.


179k miles. 3 owner, grandma spec.
I've been driving it to get accustomed to the driveline, build some trust in the engine, etc. Looooooong handbrake skids in the snow, reverse J turns, etc and all just bonuses of FWD this time of year.
I'll be pulling the ECU to send off to Hondata during my holiday vacation and will aim to tear this apart in mid January and bolt it all into the Civic then.

 

Hahaha that thing is sweet. Almost a shame to tear it apart. I always thought one of those would make a fun/nice daily, even in base trim.

That said, can't wait to see it cannibalized for golden-era honda racecar glory!

 

I was gonna say the same thing lol. Too clean. Make it your daily and find another haha.

Can't wait to see it get cannibalized.

 

Parts have been streaming in lately, and I got the major fab hurdle done. Ive got a week of business travel and a week of vacation for the holidays lined up next, but January is gonna be all reassembly and shiny bits, hopefully.

An opportunistic scratch and dent halo seat trial. I was going to do another Sparco Circuit II as I am semi long-torso and semi cheeseburger belly, but can sometimes flicker down to a 32" waist. This seat is a little wide for me, but works well for the shoulder belt hole height.


The under side hump is unfortunate. The two side mount pairs i have on hand dont work great. The Recaros are aluminum, while the NRGs are steel. I may modify the NRGs once I have my steering wheel hub and spacers here.




Moving forward, the Hasport "EFK2" mounts require removal and replacement of the stock passenger side engine mount.











Once that was complete, the next task item in the way preventing paint work and brake line building, was to remove the pedal assembly, brake booster and both the front subframe/suspension crossmembers.
It is tough to tell from cellphone camera, but this pic is after a couple days of degreaser prep and bucket washing. I dont have a hose bib in this rental unit, so I filled buckets in the bathroom sink. There was an 1/8" of axle grease coating the bottom quarter of the firewall.


This is not my photo, but an example of the cable to hydraulic conversion I am doing to drive the hydraulic K series clutch:



If i drop the lift fast enough, the project will complete itself?


The turd parked in the corner with its ECU removed and shipped to Hondata:



Build plan/parts list:
Donor car is providing:
K20a3 engine and transmission
engine harness, ECU
all sensors, alternator, etc.
both axles and the intermediate shaft

Aftermarket parts list:
Drivetrain:
Hondata Kprov4
Rywire "Race/Universal" K series chassis side fuse box/chassis harness. I will run one wire from this kit to the stock fuel pump and run my own brake light circuit.
Rywire ignition/switch panel, direct plug and play with the above. These two items replace the need for the shared chassis harness connection to the stock ECU.
Skunk2 Alpha K swap header
AIM MXm or MXq dash.
Insane Shafts 36mm K swap hubs
5.417:1 MFactory final drive
MFactory metal plate LSD
ebay vendor cable to hydro clutch master conversion.
EK/DC2 stainless clutch line.
EK/DC2 clutch master


Suspension/chassis:
PCI front upper control arms with stock bushed pivots(no spherical bearings anywhere due to rules penalty)
SPC rear upper control arms
Suspension Techniques rear sway bar. This may get replaced/upgraded later.
Honda CRX HF front swaybar, the smallest/softest OEM option. I considered building it with no front bar, but decided on "a" front bar, and the car came with the largest OEM Sedan variant. I picked up an HF bar from eBay.
The car came on a set of period correct PIC(progress in control?) coilovers. Like an early 'oughts predecessor to Feal or Fortune Auto style setup, to my knowledge. They will be replaced and upgraded early next season, potentially after the first shakedown event.
Stock lower control arms at both ends. Stock rear toe arm thingies on the stock trailing arms.
Honed brake booster delete.
EF Sedan brake master
Wilwood adjustable proportioning valve
All new custom hardlines, rear line probably ran under the car instead of through.
Stock calipers for now.
Zero aero. I am taking the BTM credit so it will have the stock Civic front bumper and rear spoiler. The shape of that front bumper makes an undertray very difficult, but that will be investigated after the motor is in and I can see oil pan depth, etc.

Wheels and tires:
Most likely 15x8 square, with 205/50/15 Hoosiers or 225/45/15 something elses. I have a set of scrubbed 225/45 Toyo RR to start the season on.
I have a set of 15x9 Rota Grid, a set of 15x8 RPF1, a pair of 15x9 Jongbloed and a pair of 15x7 Konigs.
I could do a couple different reverse stagger setups, but the NASA rules do not have an "average tire size" allowance like GLTC does, so the car will be classed solely on its largest tire, the front.
I may potentially run a square tire but staggered wheel setup, 15x9/225 front and 8/225 rear.


I have alluded to the rules and their incentivization of certain build decisions. My next post will probably be the rulebook theorycrafting post, as the choices have pretty much all been made, save for exact comp weight which will be driven by average power built on the dyno.