well when i get my turbo installed next moday. i want to pitch the idea to SPEEDFORCE to make us a low compression rotors for our FI rx8. if i get enough people to post of interest i will show him this thread, and convince him to make it. now my question is what will be a ratio for these rotors. PLEASE POST INTEREST SO WE CAN GET OUR 8's to PUT OUT MORE POWER THAN EVER.

 

I think you'll have to worry about your tranny first.

 

Why would you want to lower static compression? you would have to raise boost to achieve the same power level.....Am I missing something important here? (and I know myth has it that a high compression engine is not FI friendly...)

 

The current A/F/S tuning ability of the RX-8 is not such that you can turn up the boost enough to have a need for low-compression rotors.

And frankly, I never saw the benefit of crippling your engine, to make SURE it won't be fast until the turbo spools.

Peace
policy

 

I would like to see how the SFR unit responds before I throw money into low comp rotors.

 

i wouldn't want to buy lower compression rotors from SFR to begin with.
They'd cost a damn fortune.

I'd rather buy them from some of the japanese shops if I had a choice.

 

Nobody makes rotors but Mazda!!

 

That is not 100% true... even in Japan...

He argument is theoratically just. Since the 10:1 ratio in the renesis is too high for higher boost than we see now.

The magic figure for a multi side port engine is ..... if you can tell me than you can sell it to the rest of the world. Also take very good care of choosing the shape of the groove as well. Coz you can make the trail deeper or leading deeper or both equal (as in our rotor).]

Keep us posted

 

i've often wondered about lowering compression.

in theory, i could just grind away evenly on the bowl surface, then cc the chambers to be equal, then send the rotating assembly out for balancing.

doing it would be easy. now doing it and not having reliability issues might be another thing.

 

There are people out there that have machined their rotors down to lower compression. The big problem is that from '93 on the casting thckness has been relatively thin. I wouldn't try to boost a new rotor that has been machined out to a lower ocmpression ratio.

 

I don't think you understand how difficult it is to make rotors if you are thinking of pitching the idea to a shop like Speed Force Racing. In addition some people saying high compression adversely affecting boosted performance being a myth how about I build a 8:0:1 compression turbo motor and you build a 11:0:1 compression turbo motor which will make more power at the same boost level giving everything else equal? The high compression of course. Now lets factor in running gas with a 93 octane rating on each engine and we run the maximum boost we can run without detonation at that fuel do you still think the high compression motor running 10psi is going to make more HP than the low compression motor running 20psi? Higher compression is fine on a turbocharged motor, in fact most forced induction race cars you will find run higher than 10:1 compression. However do you feel like driving around wih 116 octane gas all the time?

 

Isn't lower compression only for reliability? so the engine last 100 to 300k

 

You have to be careful what your doing too. Its quite possible to completely ruin your 1/4 times by building a car that runs high psi, but doesn't get power till the higher revs...then you shift right outta the boost range, right into the low compression range, and bam there goes your time.

www.3si.org is an excellent example of this. The fastest "street" cars that drag, usually are the ones running smaller turbo's with lower spoolup times...when they shift, they don't drop off boost, and they'll get lower numbers then the guys dealing with the lord gigantius turbo's.

Thus if you shift, and drop off boost, in a low compression motor, your going to be at a significant disadvantage in whatever racing you prefer.

 

well see he actually pitched this tome before. but i wanted to see if there are enough interest to bring the idea back up to him

 

I don't necessarily disagree with you (not that I could even argue with you) but I much rather run a high compression, low boost application and make sure it does well with 93/91 octane gas. And when I refer to high compression I am talking about 10:1 as in the renesis.

 

I guess the issue of compression is directly related to the ability of the engine to handle heat to avod detonation?

Would going from 10:1 to 9:1 really hurt the Renesis that much in its ability to rev? The REW engines ran at this compression and you can get pretty fast spool on those and produce a substantial amount of power on pump gas.

I'm by no means an expert, so I might be completely missing the picture.

 

What was the static compression on the FD's?

Also it seems like racing beat would be a better one to petition, since they are already selling lightweight rotors. Of course if you're running that much boost, you also need a non-plastic intake and upgraded fuel system too, right? Frankly I don't think there's going to be a significant market for any of that until significant numbers of RX-8 owners have used up their warranties. That's probably a couple of years away.

 

The FD's ran a 9.0:1 compression ratio.

Mazda did compression ratio test decades ago to determine the power potential for different compression ratios. The chart is very interesting in that between 9.0:1 and 10.0:1, there really isn't any difference in power output. However going below 9.0:1 and above 10.0:1 would get you less power in both cases. Interesting.

 

well you guys are doing a good job with researching. so your say saying a 9.0:1 ratio is good

 

Rotarygod, or anyone else, running on premium pump gas the difference between 9:1 and 10:1 is essentially the same in regards to detonation and the ability to handle boost?

(I'm assuming boost as the resistance created within the intake manifold, not the heat or cfm generated by the tubine.)

 

I could be wrong but wouldn't the FD or FC rotors work? If so, why not just use the factory rotors? As opposed to making new ones.

 

FD/FC rotors are heavier, and don't have the provisions for the cut-off seals on the flanks....

 

the point is that with a given compression ratio, you might be able to make, say 300horsepower.

with a compression ratio that is lower, while you lose power off boost, you might be able to make, 350, 400 or more horsepower.

you lose a little down low, gain a lot up top. depends what you are looking for if it is a good idea or not.

 

why would lower compression allow for higher HP?

 

i dont think that the fc/fd rotors would work. i talked to tim about that idea. he said that the renisis has a different design to it. can anybody confirm this.
if not somebody tell the difference. or show me how they are similar