My friends and I bought a "ran before engine was pulled but wouldn't start hot" $400 manual RX-8 to compete in the 2026 challenge.
We are trying to decide what way to go with the car and have come up with a few options.
1. Use the stock rotary and be okay with 190hp
If we go this route; do we put the engine back in and compression test to try and diagnose more before tearing it apart or will it be evident what the issue is if we split the cases? None of us have any rotary experience.
2. Rebuild and Turbo the Renesis and try to figure out a way to tune it cheaply so that we can at least get a few thousand miles out of it before engine failure part 2.
3. Swap the motor for something else
- Something low torque so we can keep the RX-8 rear diff and trans
- Swap the entire drive train for something higher power and more torque (v8?).
If we end up going the motor swap route, then that begs the question why start with this beat up RX-8 at all? Why not some other platform or a cleaner RX-8?
We would love to hear all of your thoughts - we want our first foray into the challenge to be somewhat successful!
That looks like a fun project! I also have no rotary experience, so I have no input on trying to just make it run vs tearing it apart first, but I'm sure someone here will have a better answer for you.
Turbo for cheap sounds fun, but it's something that I'm always told to not try (I was also thinking of adding power to my 325i that I'm building for my first attempt at the Challenge). But if you have the knowledge or the time to learn how, why not try it?
Engine swap seems hard to fit into the Challenge budget, but if you can make it work then hell yeah!
Put the engine back in. Any rotary will start if you spin it fast enough- invent a fun way to do this, and make a demonstration of your 5k rpm external starter part of your concours presentation; now you've got that part of the competition locked down. Remove weight, add sticky tires, plenty of budget leftover to just make the rest of the car work as well as possible.
Okay... here goes...
Rx8 engines do not respond terribly well to turbos. The gains just aren't there for some reason for the effort and money put in.
An older s4 or s5 turboii engine will swap in and bolt to stock drivetrain and CAN make decent power.
I'm not sure why there is a "Low torque" requirement. Sure, the trans will be the weak link, but they aren't horrible. The diff is the same construction as in an FD rx7 and can handle 400+ hp all day long.
If you keep the stock trans and stock diff, you will need to get a high reving engine that doesn't mind cruising in the 4000 rpm range on the highway.
If you are trying to keep this in challenge budget, I think you have 3 choices:
- fix stock renesis engine - can be pricey.
- engine swap to something that can utilize stock trans and diff.
- engine and trans swap to something cheap and has a high overdrive in the trans.
The last one is what I chose. My rx8 has a gm 3.9 v6 mated to a T5 trans out of a 4th gen v6 camaro. Competed in the challenge the last 3 years.
Oh, I wanted to say that once you tear open the rotary engine, you are basically committed to rebuilding it if you intend to use it.
Renesis engines have coating failures on the hard parts. If this engine has a coating failure, it's new parts time. It can get expensive quickly.
If I may offer some FIRST TIME CHALLENGE ENTRY suggestions:
- Get it running. I like Nonacks idea for creative engine spinning for the concours.
- Make sure it stops/goes/turns like it should (probably in that order)
- Get some seat time with the car at a local event
- TIRES
- Remove weight
- Have fun
- If you must start developing for power and or more grip/traction do it after you know you have a running entry
The challenge is about more than raw speed. Show up have fun and see how the car performs. Then make plans for next time.
I'm with Stafford (and others) on this - it's better to show up to your first Challenge with a sorted solid running car, and do all the events, get a feel for how things go (and have fun!), learn from it, and come up with plans to do better next year.
So, if the original motor is in good enough shape to get running decently, that's the easy button to get you on your way to April.
Yes, we love insane builds, but we want you to have fun and learn, too.
- Bill C
BillCuttitta said:
I'm with Stafford (and others) on this - it's better to show up to your first Challenge with a sorted solid running car, and do all the events, get a feel for how things go (and have fun!), learn from it, and come up with plans to do better next year.
So, if the original motor is in good enough shape to get running decently, that's the easy button to get you on your way to April.
Yes, we love insane builds, but we want you to have fun and learn, too.
- Bill C
I'll second (third?) this, but I'm excited to see what you bring to the $2000 Challenge nonetheless. 
Thank you all for the insight. There is a lot of good info here.
I maybe should have clarified initially, we are doing this project for our senior design course toward our bachelors in mechanical engineering, so we need some pretty in depth design, manufacturing, and testing of at least 5 parts.
With that said, I think the option to drop the engine back in and run it as is isn't on the table for us unless we focus on altering another aspect of the car.
We are going to drop the motor back in this weekend and run a compression check to know what we are starting with before moving forward down any path. Worst case, if we sell the renesis, the buyer will like to have those numbers.
On that note, we are going to attempt to use a camera and a traditional compression tester like this forum walks through.
https://www.rx8club.com/series-i-tech-garage-22/diy-compression-test-244299/
Design, manufacture and test:
sunroof delete
Front aero
Rear aero
Short shifter
Brap cutout
SV reX
MegaDork
9/4/25 8:25 a.m.
I brought an RX8 to the Challenge. It's been 8 or 10 years.
The above suggestions to keep it simple and GET THERE are absolutely the top priority. Especially as first timers- don't overthink it.
The RX8 is a capable chassis. It can autocross well. Focus on that part. (Lots of cars have performed amazingly well at the Challenge as capable auto crossers but mediocre drag racers)
Im convinced 90% of dead RX8s do not have bad engines. They aren't generating enough spark (coil packs, wires, etc), or they have a terminal flooding problem (washes the cylinder walls with fuel which removes the surface oil and reduces the compression)
Having said all that, don't do it. You are mechanical engineers. Do something interesting! Build an electric RX8, or one that is powered by twin motorcycle engines, or a home built jet propulsion, or a farm tractor 3 cylinder diesel. Use active aero, air suspension, downdraft fans. Let your creativity explode- think WAAY outside the box! Don't worry about being competitive- be insane! You won't get many better opportunities to do it in your careers.
Renesis??? Don't be so boring!
OK another idea- these have a lot of room in front of the engine, especially if you can get that pesky radiator out of the way. The rotary is already sort of a 2-stroke, make it more of one by grafting an entire snowmobile/waverunner/other hilarious 2-stroke to the front of the existing engine. This could also solve your "spin it fast enough to start" problem if you do it well.
Bonus points if you put one or two more in the back and link them to the driveshaft/diff somehow, maybe via a snowmobile CVT.
We dropped the engine back in the car this morning and hooked it up enough to turn it over for a compression test.
Everything went back together smoothly, lots of room in the trans tunnel of this car!
We were seeing about 10psi on the spikes with the pressure relief valve held open. With the pressure relief valve closed it peaked around 30 psi. This was uniform across all 4 of the spark plug holes.
Does anyone know if this low of compression could be due to the engine being cold / not running in a few months?
We are assuming that we have some bad seals inside (or maybe a bad testing method) but are hoping not.
Did you take the little check valve out of the tester?
30psi is bad.
Put a couple spoonfuls of mmo or oil in the chambers and try again.
Hold the throttle open.
It can also be low due to slow turning over. Battery has gotta be topped up and starter in great shape.
In reply to wvumtnbkr :
We just ziptied the schrader valve open, didnt actually remove it.
It seems like it wouldn't even run with the number that we got. Throttle was open fully. We will add some oil and retry.
The car didn't come with a battery so just jumper cables from my 4runner to the terminals, didn't sound like it was spinning abnormally slow but definitely not fast..
Not sure how you ziptie the Schrader valve open. It's in the base of the gauge or hose. You can't see it or get to it with the Guage and hose assembled.
https://www.rx8club.com/rx-8-discussion-3/piston-compression-tester-can-check-rotary-273378/
Oh, something else I just thought of... you did leave the leading or trailing spark plug tight in the chamber while testing, right? At least 1 spark plug per chamber has got to be present or all of your compression will blow out the other one.
This ought to be an interesting project!
