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Fate is a fickle thing. Plan one way, and BAM! an opportunity to do something COMPLETELY different gets dropped in your lap. In my Alternate Builds build log for Justin's Vicky, I had planned on initially using a 4.6 mod motor. Then rethought that and figured I would be better off going with an ecoboost. Tonight, however, I had this dropped in my lap: 2008 RX8 engine with 125,00 miles, six speed trans, engine wiring harness (no ecu). for $1,600 bucks. I have never worked with rotary engines in the past, but I am a fast learner. I also think it would be an opportunity to show Junior how to think outside the box. I haven't seen too many street rods running around with a rotary and a six speed. Street rodding has gotten much more accepting of "Other" engines in these cars, so I don't think we will be run out of town on a rail if we do this. Like to hear back from guys that are running the rotary engines on the pros and cons of going this route. I'm running a dana rear from a 2004 GTO, that has a 3.34 ring and pinion. Car should weigh in at around 2,600 pounds (I know, a behemoth in this crowd).

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Dismantalus, Fabricatus, Assemblus.....
Certified Welder, Certified Welding Inspector, Full Time Car Freak...In New Jersey no less!

Currently racing an RX8 while I build the locost..

Ok so the RX8 has a 4.77 rear end stock, so that's one thing to keep in mind. With 245/45/17 tires I am about 65mph in 2nd gear when I hit the limiter. Power below 4k is ..lacking.

Do you know the health of the engine? Getting a compression test would be a good idea, and make sure you know how to do it on a rotary engine. For any parts you may need, including rebuild kits, I recommend Atkins Rotary. They have always been good to me. Just go with OEM apex and corner seals, anything else is a lesser part.

For longevity, I use a sohn adapter and premix at about 1:200 with any JASO FD 2 stroke oil.

Good luck. I seriously considered a Renesis for my locost before settling on a bike engine.

I built my Locost using the 13B running gear from a '91 RX7. I chose that to learn about the engine as I had never had a rotary engine before. Mine required a complete rebuild with 1 rotor and 1 housing being replaced with good used parts. I am not a rotor head, just a person who decided to go that way for that build. It was a great experience. I am glad I went that way. Others may be able to give you better rotary advice than I would. I don't think that I would go that route again just because there are so many other possibilities today.

I "think" that 2600 lbs with the diff ratio you are proposing (3.34) may be a bit slow off the line and maybe underpowered. However, the original RX8 was 3,045 to 3,075 lbs so maybe not "that much" worse than the original application?

My rotary did come alive between 4k and 8krpm. Not exactly a cruising motor, but a fun one in a sports car, no doubt!

I'm not sure about the OMP on the RX-8. It may require the OEM ECU or some 3rd party special controller as my RX-7 did. You may want to check that out as it may limit your ECU options. The Sohn adapter mentioned y be a good idea. I just blocked off the OMP on my 13B and premixed TWC-3 oil at 125:1. It was a bit of an inconvenience but not insurmountable.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

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I concur with what has been mentioned about the torque-less low rpm of the naturally-aspirated rotary. I wouldn't consider anything lower numerically than a 4.10 for the ring and pinion. The Renesis is not amenable to turbocharging if you were to put it in and then think you could improve the bottom end by boosting it. The rotors are 10:1 compression, but they can be replaced with 3rd gen FD rotors. But, then you still have the restrictive exhaust path in the Renesis side housings. If you think that this is a likely progression, just start with an FD engine.
I'm not trying to discourage this engine in your project. It would be a neat combination if you address the gearing.

Thanks everyone for the replies so far. This is the kind of feedback I was looking for (and expected from the good folks here).
RX7locost, the 3:34 is just what is in it now. It's a Dana rear, so a 4:11, 4:56, or 4:88 for it is just a phone call to Jegs away. So that will be easy enough to address. I plan on procuring an oem ecu, since I will need one to get through inspection.
seven13bt, I think that the normally aspirated version will be fine. I'm not going to mess with aftermarket stuff here. One, because I'm not really proficient in turbocharging, and two, because of the expense and possible reliability issue. She's being built to drive and enjoy. So the obvious answer is to just address the gearing.

I just got off the phone with Jegs. The steepest gearing available for the GTO 7.75" rear is 4:11, @ $500+. I haven't done any brac*ets for the IRS yet, so I could still use the rear I originally set up, which was an 8.8 from a 1988 Mustang. It has already been narrowed to have a 57" hub to hub dimension, with the New Style Torino bearing housings to eliminate the c-clips. R&P is $180 to $200, 4:11, 4:56, or 4:88. That's a tough call. Give up the IRS, r&P difference almost covers the cost of the axles. Engines and axles and transmissions, oh my! This is going to be a tough one to get my head around.
Ok, so it looks like there are decisions to be made.

Thanks again to everyone for the input so far!

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Dismantalus, Fabricatus, Assemblus.....
Certified Welder, Certified Welding Inspector, Full Time Car Freak...In New Jersey no less!

Hmm, for my build I am using a 7.5" rear end and can find as high as a 3.7x R&P in the junkyard without breaking a sweat. I was talked out of an 8.8 due to the weight. Even this 7.5 is very hefty. In your shoes I would look at a 7.5 or IRS..

Thing is, I already HAVE the 8.8. And the 7.75 Dana IRS. But I think the decision may have already been made for me. I can't get the proper ride height with the wheels and tires I'm going to be running, and still clear the transmission tunnel. I'd need to make a new tunnel, and it would be about 4" taller than the stock one. No bueno! If I stick with the 7.75 Dana, I can keep the pumpkin at a height that clears the trans. tunnel, with my half-shafts angled upward from the pumpkin about 5*. Keeps my ride height at 6" front, 7" rear for a good overall height, and a nice hot rod rake. Allows me to use the
26" diameter tires from the C4 Corvette that I have. If I swap in the 4:11's, I can use whatever power plant I want, as I'll also be using an overdrive trans, so no harm no foul.

I think the only real decision now is whether or not to pull the trigger on the Rotary. I do so love the idea of seeing the look on peoples faces when the hood opens... and there sits a Rotary!

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Dismantalus, Fabricatus, Assemblus.....
Certified Welder, Certified Welding Inspector, Full Time Car Freak...In New Jersey no less!

Since Jr. and the Wife will be the ones that will probably end up driving the Vicky to shows and whatnot, I decided that the rotary setup might be a bit "difficult" for them. There is another option, though.
I COULD take the Tuned Port L98 / Super T10 that was going in the LoCost, Put THAT in the Vicky (That's what it was originally sourced and built for), and get the Rotary to put in the Locost.
There is only one real question on this avenue. The best I can do for a Dana 36 is a 3.73 ring and pinion. With that said, estimated weight for the LoCost is around 1600-1800 lbs.
With a 3.73, and the six speed trans also fitting the Duratec bellhousing, an ecoboost would not be that difficult down the road, should the rotary ever sh*t the bed. I'm kind of in uncharted territory with the Rotary, so any other comments or observations would be appreciated.

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Dismantalus, Fabricatus, Assemblus.....
Certified Welder, Certified Welding Inspector, Full Time Car Freak...In New Jersey no less!

Considering that the first gear ratio is 3.76, the significantly lower weight and probably a smaller diameter tire than 26", this would be OK in a locost with a 3.73 ring and pinion.

Thanks for the input. I'm kind of locked into the diameter, as the whole suspension is C4 Corvette. I may have actually just pulled a rabbit from a hat. I forgot I had the differential from my old '72 Vette in the shed down back. I can get a 4:56 for that one. It will mean re-doing the rear differential mounts, and making up brackets for the toe / camber links, but that is not a huge problem. Especially since I have not finish welded the chassis yet.
I'm warming up to this possibility.

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Dismantalus, Fabricatus, Assemblus.....
Certified Welder, Certified Welding Inspector, Full Time Car Freak...In New Jersey no less!