The only one I know of that has done it was Guitarjunkie but I can't ask him. I don't know if Lucky7 has knowlege with it or not.

I know Mazdatrix tried it and claimed no significan't gains. As far as I know they bench tested it and no dydno. But that aside, price is more important then power gains. I can buy 3 RX8 rotors for the price of two RX7 rotors.

Yes I know they are high compression and I consider 14lbs low boost but i'm sure there will eb several people repeating that anyhow.

The problem is the Renesis has side exhaust so what needs to be done on the RX8 rotors for this not to be a problem in the 13B block?

 

You have to run the renesis side and corner seals since the side seals were relocated outward. IF you are running these in a peripheral exhaust motor like an FD, you have to run the taller apex seals for the older 13b as the renny ones are made shorter since they will never flex passing over an exhaust port. This means you have to mill the renny rotors out to fit them. The problem is, the renny rotors are cast fairly thin, and I have heard reports from other builders that have tried milling them only to break through (even when only milling for taller 2mm seals).

The extra oil control/cutoff ring on the side is irrelevant, you just leave those off and don't worry about it.

This would be a high comp turbo setup and you'd have to be extremely careful on the tuning end. I have built several such motors but mostly for stock or near stock cars that I wanted to build "on the cheap" just to drive around, not to race. Most tuners want to go to 13-15psi on pump gas on a low comp turbo motor, and they will be even more afraid of a high comp version.

That said, I have seen as much as 22psi run on high comp rotors before and the engine survived.

One more thing...the renny rotors being cast thin, along with being high compression, will make them easier to dent the faces in. This isn't usually regarded as an actual failure, and you never know it has happened until the engine is torn apart the next time, but some rebuilders won't reuse dented rotors so that's another consideration.

All in all, we have a hard enough time keeping these cars on the road, as they run on the ragged edge as it is. There's not a good reason to push yourself even closer toward that edge unless you really know what you are doing or you just don't care. I would recommend a more conservative approach, not that I am afraid of trying new things, but just because the average person doesn't need any more headache and worry than the car already presents.

 

Great post Kevin, very informative

Personally, I've never felt the need to run anything other than FD internals in my motor. Built and tuned properly, it's more than capable of making monster power.

 

Well the main reason is price. Like I said I can get 3 Ren' rotors for the price of 2 13B rotors. I can get two Ren' e-shafts and a tank of gas for the price of one 13B e-shaft.

If the tuner is good then the compression shouldn't matter. If I get the same results at 10lbs vs 15, what's the difference (still be same fuel). I don't really consider them high compression (it's not much higher then 9:1). What's the compression on a twin turbo Lamborguinni? My bike is 15:1 but yeah I know it's not a turbo.

I wasn't aware of milling them for FD Apex seals. I was told by Mazdacomp that I had to use RX8 seals. Milling them would offset the savings.

 

If you try to use the short renesis apex seals in a peripheral exhaust motor you will likely warp them in short order, as they flex more than the taller/thicker ones. Mazda shortened them in the renesis to allow for less mass in the seal, to respond better at high rpm's (9k+) where traditional more massive seals tend to float or flutter.

Yes, compression will matter. Again, most tuners like to set up for 13-15psi on pump with standard 9.0 compression rotors. If you tell them you have high compression rotors they will look at you funny and probably only want to go 12-13 max.

No, you will not make the same power at 10psi on highcomp rotors as you would at 15psi on lowcomp. It's more like, with both rotors at 10psi, the highcomp will win out by a few hp, at the cost of higher chamber pressures and temperatures and possibly the longevity of the engine on a larger scale.

Also, 10:1 may no be "high compression" in the piston engine world, but we are not dealing with that here. There is always a 'rotary conversion factor" involved when making calculations. A t78 turbo on a supra can make 600-800hp, while on a rotary it maxes out around 500. While 15psi on a piston engine is stock boost for some cars and 20-25 is normal for modded street cars, 15psi is a considerable boost for a rotary and 20+ is pretty much race only. A piston engine might be able to make 500rwhp with XXX amount of fuel while a rotary needs XXX + YYY to make the same amount. 1.3 liters of displacement in a rotary makes twice the power that it might in a piston engine.

By the same token, 10:1 is not high on a piston engine but is high on a boosted rotary. Even so, even very few piston engine guys choose to run 10:1 compression on boosted setups; they either do so out of necessity (they dont want to open the bottom end) or for a specific purpose (maybe they run on meth or alcohol and can tolerate it better). Most boosted piston engine setups run 8.5-9.2:1 CR.

Sure, the parts are cheaper, but is a couple hundred bucks worth a premature trip to the engine rebuilder that'll cost you a couple *grand*? Again...these setups seem to be challenging enough for many people to hold together, why ask for more trouble?

Yes, the renny shaft is cheaper and better, but unless you need a shaft already, there's not really a reason to abandon the REW shaft. They have been proven capable to 9krpm, which most turbo rotaries will never see or exceed anyway because most turbos cannot flow that much on the top end.

 

How about 1mm ceramic apex seals, would that help to prevent the warping?

 

NRS doesn't make ceramic RX8 seals. I'm not sure if Ianetti does or not. I was going to ask if ceramic would solve the flexing problem to.

Good info RotaryResurection. Thanks for the replys

 

Yes, ceramic seals would be nice, but none are made for the application at this time. You'd still be stuck with milling the floor of the renny rotors for the taller standard seals. Some people claim that they have had no issues at all doing this, while others claim that they have. I for one do not plan on doing much experimentation with rotor milling on renny rotors, given the rarity of used/core rotors, and the cost of new ones.

 

I also don't think higher compression and a turbo is a good idea on the rotary.

I just rebuilt my engine with 9:1 CR rotors and 2mm seals instead of my usual 8:5 CR rotors and 3mm seals.

I had been running 15 psi boost on 91 octane (~89 octane with 1 qt premix) for 20,000 miles on the 8.5:1 rotors.

With the new 9:1 rotors and the same old conservative tune the detonation was so bad the whole motor hesitated and power cut out until I backed the boost down to 12 psi boost. The detonation eroded/vaporized the ground strap off my front leading plug.

With 9:1 CR below 3,000rpm boost response is slightly better, but full boost is still same RPM and power does not feel any better.

Basically, you gain some driveability with the increase in CR ratio at the expense of ultimate performance.

Mazda Motorsports offers ceramic RX-8 seals- probably Ianetti. $$$ though.

I have heard many times that the stock RX-8 seals are not as tall and will distort going over the peripheral exhaust port, but the top part of the 3 piece seals is very short itself. Is it supposed that the support of the bottom piece keeps the top from distorting?

I am hoping we get extensive E85 distribution as I would like to someday try the RX-8 rotors in a turbo application so that I can take advantage of the sideseal location and the chamfer and port for even earlier opening timing on a streetport.

But for now I am looking for more 8.5:1 rotors for future builds.

 

There are turbo kits for the RX-8. yes, lower boost (about 8lbs) but then OEM boost on the RX-7 is 10lbs.

I've had two engines at about $6,000/ea lat about 1000 miles before breaking an apex seal and limping another 500miles before I rebuild. That's over $12,000 for 2,000 miles!!!

If I get more then 1,000 miles with RX-8 rotors then i'm doing better then my previous professional rebuilds and tuning.

 

So, after numerous post stating its a BAD idea (I for one am another in favor of it being stupid) and complaining about spending $12,000 on rebuilds your gonna STILL use the RX8 rotors which makes your tune even more critical and all for saving a buck??? WTF? Buy some used s4/s5/s6 rotors, there CHEAP and theres nothing to wear out but the seal grooves and unless its a HIGH mileage engine or heavily abused, you'll find that those grooves last a LONG TIME.

~Mike.........

 

Renisis Engines are junk for turbo'ing....dont do it.

Post a WTB ad looking for S5 Turbo rotors.

Also, theres a reason why your only getting 1000miles on a fresh rebuild, either your setup is totally wrong or your tuner cant tune.

 

This is what is known in builder/tuner shops as "job security".

 

He's talking about using rx8 rotors in an FD block not a side port renesis.

Or he should save money and just use the s6 rotors he already has(unless they are damaged) IIRC s5 turbo & s6 rotors are 9:1.

 

i agree. i think you're skating uphill if you plan to use Renesis rotors in a turbo application - RR hit every point i would make, so there's no need for me to detail the reasons not to. cost is no justification in this case ... sorry. whatever money you save in parts will be more than spent in tuning. i can see that you're not cheap from your signature, but i really think choosing rotors based solely on cost will be a hard lesson. you got burned twice and it sucks, but i think what you need to change is your tuner/builder.

 

Iannetti
>> versions...1300 bucks a set...for the seals. dave at kdr will be building my 90 na motor with the rx8 rotors and e shaft. but to boost them i dont think i would they were made to be in a n/a car for a reason. good luck though.

 

Ianettis for 1300 bucks a set? Last I heard they were closer to 2 grand retail.

Everybody likes those NRS, and for about 1200/set that is probably the way to go.

 

or dont know break in procedures

 

The Ianetti seals for the RX8 with Mazdacomp discount/sponsorship cost $900 for a set of THREE or $1,800 for the full set.