A Tale of Two RX7's and Scope Creep: My 6+ Year Build

In reply to dannyp84 :

Sorry, haven't been on in forever. The majority is 1/16" wall 304 SS, if I recall correctly. The collector/merge/expansion assembly is 1/16" 321 SS. Everyone told me 1/16" wouldn't hold up even if it was SS. I don't recall how old it is now but everything appears to be holding up fine (as long as I don't hit it against anything hard).

I really need to update this. 2024 has been kind of a bust because I exploded 2nd gear at VIR in March. That's been corrected but it's looking like I'm only going to get 2 events in this year. Next up is the NASA Fall Finale again at Summit Point.

Hey! I have the EFI Hardware ITBs on my car and am in the process of building a harness for my Fuel Tech ECU. Would you recommend attempting self tuning (doing as much research prior as I can)? Or is this setup too complex for a novice in tuning to attempt and best left to professionals? From reading your story, I believe it sounds like you self tuned for the first couple years prior to taking it to angel motorsports/other tuners.

Also, I believe in one response you said the EFI Hardware kits were great outside of the return spring for the throttle. Which return spring did you upgrade to?

One final question is would a street car see as high of IATs as you see? I understand you fought that for a while, and I have the K&N filter that you ran for a little while before designing the air box and a heat shield.

Anything else I should know would be greatly appreciated! The progress photos and story telling has been great, I have read through this a few times already.

 

In reply to infernosg :

I ended up using 321 for my header then 304 behind that. I've had transmission issues with my FC as well, and I just installed one of my used spares for this coming race weekend. If you'd like to earn a little cash to put toward your racing program this winter, I'd be happy to bring you the damaged transmission for a rebuild. I'd like to have at least one totally fresh gearbox that I can trust, and do a better job of protecting it from heat once it's reinstalled.

In reply to Nap :

In regards to tuning I had a lot of help along the way. Chris Ludwig at LMS EFI got me going with a basic base map. His shop completely built my engine harness and the base tune was something he did as a favor. I wouldn't expect him to do anything like that for free. Beyond that, in the first year alone I had a couple other "friends" take a look at the tune and make some tweak to get the car starting and running better. From that point until I took it to Angel Motorsports it was really all just me trying to get the VE table cleaned up, improve cold/hot starts and stumble blindly through transient throttle settings. It wasn't until late 2022 that I really got a tuner to focus on the car and it's been a total difference. I'm not familiar with FuelTech but my understanding is most of the aftermarket ECUs are similar. It's definitely something you can do yourself but you'll want to do a lot of research first.

For the throttle, every EFI throttle body I've had I've needed to add external springs to increase the return tension. I'm sure there are more elegant solutions but I just run one or two linear springs to a plate that are also attached to the cam on the throttle. The problem is without this extra tension the airflow/engine vacuum holds the throttle slightly more open - in my experience throttle position changed by 0.5-1% between engine off/on.

Regarding IATs the highest I ever saw was while driving at lower speeds through traffic with that K&N filter. It was just sucking in hot air from the engine bay and, IIRC, it got to nearly 150F. I don't do too much street driving anymore but I think the highest I see with the airbox is around 110F on hotter days. While moving it's generally no more than ~10F above ambient temperature. I definitely recommend making some kind of airbox/cold air intake. 

In reply to dannyp84 :

My transmission had a good run. The failure is definitely my fault. I bumped the inside curbing coming out of turn 12 at VIR (Oak Tree) at WOT, I'm pretty sure the momentary loss of traction, even with the LSD, then sudden regaining of traction at full demand on hot, sticky tires was too much shock for 2nd gear to hold.

LOL, thanks for the offer but I determined rebuilding transmissions just isn't worth my time and I'd rather pay someone else to do it. It's not terribly difficult if you have the right tools, though. I ended up sending mine to JO Motorsports in NC. He came pretty highly recommended by all the Spec Miata guys at VIR (what better place to blow a transmission?). I think it ended up being around $1300 for all news parts (except the housings) as well as a handful of modifications/treatments to hopefully improve durability and shifting. Still kind of breaking it in and won't know for sure until Summit Point in November.