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Engine selection for FD chassis

Old 01-15-08, 10:33 PM
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Engine selection for FD chassis

I'd like to draw on the experience of you guys on this board.

I'm contemplating buying an old FD race car to run in NASA PT. The thread about Rob20rx7's FD race car build gave me lots of ideas and got me thinking about engine selection and swapping in a normally aspirated rotary.

The reason for going NA would be to simplify things rather than deal with all the issues around trying to race a turbo powered rotary. The donor car still has the factory twins and nothing special in regards to cooling. Going single turbo and also developing sufficient cooling is out of my budget.


I've been doing some research on power expectations from a normally aspirated rotary and lately I've been fixating on a Renesis motor and tranny swap. It seems like the power levels of a stock Renesis are pretty close to a well built big street ported motor. Am I correct here?

I prepared a list of benefits vs negatives below that I've been trying to validate and think through.

Renesis
benefits:
- low mileage motor probably doesn't need a rebuild
- Cost
- OK power level
- NA reliability
- Manageable sound levels

Challenges / Negatives:
- custom fab motor mounts
- custom fab PPF
- ECU (hoping that a Megasquirt could be used as a standalone but no one has done it yet that I know of)
- Renesis Fuel rail needs to modded as it is a returnless system

Street Port S4/S5 combo 13B
benefits:
- Ease of install
- NA reliability
- Megasquirt proven to work already
- Manageable sound levels

Challenges / Negatives:
- Cost to source the parts and build the motor may be high
- Power levels seem to be less than a Renesis

Bridge or P Port
benefits:
- Ease of install
- NA reliability
- Megasquirt proven to work already
- Higher power levels

Challenges / Negatives:
- Cost to source the parts and build the motor may be high
- Power levels seem to be less than a Renesis
- LOUD sound levels
- Would require some kind of scatter shield for the clutch.
- Probably not as easy to drive as a street port
- Requires custom intake

Some direct questions that I've been trying to find reliable answers on:
- Are the HP and Torque levels of a decent large street ported motor similar to a Renesis?
- What would you expect the cost to source a donor S4 or S5 motor and port and build it should be? What power levels can be expected?


It also seems that having a 6 speed would help overall performance through closer gearing to help the lower powered, lower torque motor (compared to the stock FD tranny). It would probably be beneficial to change Rear gearing to a 4.77.


Any thoughts and input would be greatly appreciated. Thanks.
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Old 01-16-08, 12:44 PM
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What I would be concerned with is what group under PT you would get put in depending on your engine choice. That may also sway your decision. If some built S4/S5 motor is going to push you into Super Unlimited, you'll be at a huge disadvantage. I don't think that would necessarily happen, but you might email them to find out where you would end up based on your selections and go from there.
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Old 01-16-08, 12:57 PM
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Bridge port and P-port power levels are much higher than you think. No renesis would come close to a real racing bridge port or P-port motor. The only reason to run a bridge port is if the rules do not let you run a P-port motor. There are a few west coast shops that sell P-port housings and intake manifolds. A good reliable 350+ hp Peripheral port motor, complete from carb to engine to exhaust header will cost about $7000, and last a long time.

I ran a NASA race weekend last March with my P-port 1st gen IMSA GTU vintage car, and was classed in Super Touring 1. I won my class. I can meet SCCA and NASA road race sound level limits.
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Old 01-16-08, 01:02 PM
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Mahjik - yeah, I'm working on figuring out classification. I don't want to race any SU class. My pockets aren't that deep.

speedturn - For sure the Renesis doesn't compare to a Bridge or P port. Thanks for the pricing info. I definitely can't afford a P Port motor and accessories.
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Old 01-16-08, 02:38 PM
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Too bad for me, (and Mahjik), there is not a NASA presence in kc area. Why don't you see if you can get an FD with a 13b homoligated to run EP in the scca? I would follow right behind you.
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Old 01-16-08, 04:01 PM
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I can't imagine getting a regular old FD/TT motor cooled will cost you more than going with any of these custom setups... and wouldn't the car be more likely to be legal for lower classes if it's nearer to stock config?
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Old 01-16-08, 07:24 PM
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Peter - the car in question (not my street car) is already a race car but uses a stock port motor and stock twins. I have other reasons for not using the existing motor setup.

ebb- Eprod is already ruled by plenty of rotary powered Mazdas. The nationals race was awesome to watch. It seems like a good class also. If I wanted to race EProd, I would definitely look into a car that is already built to that class. I've seen a few RX3s and Rx7s that are competitive.
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Old 01-16-08, 09:16 PM
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Originally Posted by gracer7-rx7 View Post
ebb- Eprod is already ruled by plenty of rotary powered Mazdas. The nationals race was awesome to watch. It seems like a good class also. If I wanted to race EProd, I would definitely look into a car that is already built to that class. I've seen a few RX3s and Rx7s that are competitive.
He knows. He's building an IT 1st gen right now as well as helping another friend build his E-Prod 1st Gen. All of whom are friends and acquaintances of the Midwest SCCA RX-7 racers.

He would just "prefer" racing a 3rd Gen body in a less expensive class than the GT classes.
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Old 01-16-08, 10:46 PM
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That is exactly right Kyle, you are on to me. Why hasn't anyone done it?
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Old 01-17-08, 07:21 PM
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A couple of thoughts on the Renesis. First, you don't need the Renesis tranny, the FD tranny will work and I know this for a fact as I just had one bolted up and cranking to do a cold compression test on a Renesis shortblock.

Second for track use the megasquirt should not be too bad, you can wire all the intake valves to wide open high rpm mode and you will lose very little. Then all you need to do are fuel and ignition.

Thinking out loud you might even be able to use the stock FD harness with an aftermarket ECU and swap out crank trigger etc with a little bit of work.

You will definitely need to come up with a throttle body solution as the RX-8 is drive by wire.

Oh, and I happen to have a renesis short block and intake manifold I'll sell you.

Steven
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Old 01-17-08, 08:57 PM
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Originally Posted by ebb View Post
That is exactly right Kyle, you are on to me. Why hasn't anyone done it?
Nevermind that, I found the answer to that question today.
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Old 01-17-08, 09:02 PM
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Old 01-17-08, 09:32 PM
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It is simply because the car never came without a turbo. You have to run an engine that it was sold with, hence the 12a or 13b choice for 1st gen. 2nd gen cannot run the turbo, and putting a non turbo 13b in a 3rd gen is not allowed because it was not available when the car was new. This info is straight from someone on the crb, not my interpretation of the gcr or anything. If they allowed it with the 13brew it would already outperform anything in EP even at stock weight, so really no place for it except GT with a peripheral port. Way out of my league. Of course you could still race one in a regional only unlimited class, no thanks.
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Old 01-17-08, 10:29 PM
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Damn rules...
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