hey guys, just curious, im doin a rebuild and wanted to do a few things, was thinkin bout a rx8 ecentric shaft in my 3rd gen. i know its lighter, and saposevly a direct fit from what im readin, but my questions were... when i go to a light flywheel, which counterweight do i need? 13b one still work? or do i need to go with the rx8.. or am i getting myself into way more then is worth it?. also, the lighter shaft will help it be a little more responsive im guessin.. not lookin for major hp numbers just response and a fun drivin car.
any info would be greatly appreciated..
thx

 

bump

 

bump again, really intrested, any info would be great..

 

you are better off calling some one that rebuilds rotaries and find out. I would start with Racing Beat.

 

Try Pettitracing. Ask Cam. He would definetly know the answer..

 

As far as I know, there is no reason to put a slightly lighter (I don't even know if that's true) or aftermarket eccentric shaft on a near stock car. Since the mass is so close to the center of rotation, it would take a huge difference in mass to make a noticable difference in response. I'd put more effort into longevity mods like lubrication (2-cycle mixing and OMP adapters, cooling).

Counterweight: Since counterweights are adjusted to counter-balance the rotors, you would generally use the counterweight that matches your rotors. However, you may want to have you rotating assembly re-balanced if you change components like an e-shaft.

 

I just found this on Atkins Rotary RX-8 Eccentric Shaft

 

I wouldnt do it unless my old e-shaft was toasted, not much to gain there. The biggest advantage to that renesis shaft is that it is really cheap to get a new one.

 

thx alot guys!
really appreciate the input, ill look into it more and make a few calls.

 

yeah i was told there like 169 from the dealer

 

Hmm, so a pound less at 8000rpm would not make a diff? Hmm i guess this goes with the fact that a 13B rotating assembly can be 0.0050" off and still be considered within spec, lol.

Anyway through, yeahm why not get your rotors lightned at RB instead? IMO, it would probably help lots more than a new shaft.

 

Counterweights match the rotors not the Eccentric shaft. So if you're using FD rotors use the stock FD counterweights. The Rx-8 shaft is a direct fit and will help with your bearing life especially if you like living at redline.

 

The Rx-8 eccentric shaft wont hold.

 

as far as i know (since i was going to do it) that you'd have too much work ahead of you. i know that the diameters between the 13b eshaft compared to the renesis shaft are different sizes and that you would need some customizing. yeah it does shave some weight but definately not worth it. i just ended up buying a used eshaft from a newer fd. call mazdatrix and ask for kyle if you still want the rx8 shaft because he was the one talking to me about it.

 

Kyle must only sweep the floors and answer the phone

It's a direct replacement.

 

i would love to get a deffinate on this. Any reduction in the weight of rotating mass makes it easier to get going and there for more hp. I'll keep checking back to see where this goes

 

wow back from the dead!

 

Yeah, but if he had started a new thread, the repost ****'s would of started crying.

 

i was going to do this to my FC but i read somewhere that the rotor bearings are a different size i dont know if this holds true for FD cars but im running a lightened flywheel on my old FC and i noticed a considerable difference in throttle response especially when i went to gear down i just tapped the gas to bring the revs up the first time and they went way up. really nice for gearing down but on the road it just stalled easier when taking off but that was about it. i drive in mountains a fair bit and less mass really helped cuz i was always shifting but the 2pounds lighter at the center which i believe is the difference probably wont do much unless lighten rotors flywheel and e shaft that might make a big difference for the cost though it may not be worth it unless your trying to hit over 10thou rpm but then you may want to run ceramic seals and thats even more there. let me know if you do it though im still curious if it would do much

 

the rx8 e-shaft is indeed a direct replacement, no bearing issues or anything else.

The weight difference being pretty much the exact center of your rotating assembly wont have much effect. Lighter rotors while still not a huge difference would be much more noticeable. Neither of these will be nearly as noticeable as shaving off a few pounds from the flywheel which has its weight much further from the center of rotation and increases rotational inertia significantly. All these together will add up as every little bit counts, but I wouldn't put in the rx8 e-shaft expecting to notice much difference.