What is limiting reliable HP and how to get past it?
Ok, like the title says I’d like to start a discussion on what limits our horsepower and how to get around it. First I’ll share what I think.

I believe we have most of the answers now. The problems we have with engine reliability stem from three things:

Not enough octane:

The combustion pocket shape makes it highly susceptible to knock, this is partially countered high surface area and the combination of water/oil cooling. Octane becomes more essential at higher RPMs, and at higher compressions. Since our engine runs at high compression and high RPMs it needs high octane out of the box. Add boost and it gets worse. This is why we have seen decent gains NA with e-85.

Solutions: Race Gas, E-85, Water injection.

Not enough cooling:

As stated above the combustion pocket is cooled on both sides. Operation in boost adds a little bit to the heat load to everything. Backpressure keeps the pressure in the combustion chamber from dropping as far during the exhaust phase, which keeps temperature from dropping as far, which raises the average temperature the rotor is exposed to, and increases the temperature parts of the housing and irons are exposed to. This also increases the average temperature the leading spark plug is exposed to.
Putting an intercooler in front of the radiator makes the cooling problem worse.

Solutions: Water injection, Additional Radiators, Oil Coolers, Colder spark plugs.


Improper Timing:

Ok, this one is going to get me flamed, but I think timing is a huge issue. Because of the compression difference we will inherently run less timing then other rotary engines. The cooling and octane issues are amplified with bad timing. Detonation leads to more heat transferred to all surfaces including the spark plugs, eventually that heat transfer causes power to be lost, and after that it leads to engine damage either from the detonation or from preignition. Even if the timing doesn’t lead to immediate engine damage, the increased heat transfer to the side irons will cook the side seal springs. But on the other side of the coin running too retarded will cause high EGTs and damage side seals, or at least that’s the current belief.
Split is a bit of black magic. You can get higher power with smaller split. In theory you could even run a negative split in boost for power gains, but if you ever lean out unintentionally engine destruction will quickly follow.
I’m currently working on different ignition timings and testing the water. Still waiting on aspects of my build to support further experimentation.

Solution: Push a fairly conservative timing, looking to limit EGT instead of pushing power. Run a higher split at higher boosts. Possibly disabling the trailing plug at high rpm (since blanking is not an option for idle). Push boost instead of timing. This is not a comprehensive solution, it will evolve as more people are successful.

 

Larger text man, I am getting old, Let the zooming commence.

 

I agree with all your points. The quality of the tune is key as well.

Right now I have an extra radiator in addition to a larger aftermarket radiator, I run Evans waterless coolant, the turbo is on it's own coolant circuit with a reservoir and pump, and my secondary oil cooler is a large BEHR unit from a Mercedes S class. I really have to beat on it to get the coolant or oil temps much above 200F but after a long session of driving hard in boost I can get my coolant temps to 220Fish. With my system letting off the gas at cruise will drop the temps back down within seconds. But I do have issues with what I consider to be overcooling so I am OCD about letting the car warm up fully. I still worry about oil temps being too low during normal cruising but I emailed Mobil1 and the tech there told me that as long as the oil was above 160F it was just fine. I also use 93 Octane only.

I am in the process of sourcing everything to go with the Adaptronic and make the switch to E85 on my current setup and then depending on how that goes, I will be making the switch to the top mount kit I got and a larger turbo.

I also may add an intercooler sprayer and possibly water/meth injection but we shall see if that is really needed.

 

emissions and side exhaust ports limit the hp on a renny

 

Emissions? And yes the side exhaust ports are a limitation but what that limit is, is yet to be seen in my opinion. A few people are doing some things now that have not been done before so I think the max HP figures as well as reliability at 325WHP+ will be improved.

People get caught up on HP numbers a lot but IMO, if we can achieve 350WHP reliably that will be plenty. I doubt I am at the 300WHP mark and I am pretty damn happy with it right now. But I love to tinker so I will try to get what I can out of the Renny.

 

isnt emissions and mpgs the reason for the side exhaust ports?

 

Yes, in part. But remember the Renesis in NA form makes close in WHP to what an FD made stock (210-215WHP or so IIRC) with the twin turbos.

 

The side exhaust ports don't help, but the compression and high rpm is what kills us.

I have a theory that if you shift the powerband lower with higher boost at lower rpm you can get reliable HP gains and a near flat HP line somewhere around 5k+. It's what I'm trying with my own build, and it looks good so far.

I'm shooting for a boost profile like this
3000 -> Starts making boost
3500 -> 10psi
4500 -> 18psi
5000 -> 16psi
7000 -> 11psi
9000 -> 9psi (or less)


I also think high boost at 7k+ won't be possible without a lot of water/meth and/or really good fuel, because the engine just won't support it and it doesn't mater how well you size the turbo and intercooler. Sure there have been dyno queens that have hit high numbers then grenaded within a month, but I don't think many of us are looking for that.


I'm excited to see what e-85 does because there is a lot of potential there. I'd try it myself, but it's not readily available to me.

 

Yeah I think that may be a good theory. My turbo (custom T618Z, larger billet compressor wheel and larger turbine wheel that is SUPPOSED to be around 44lb/min) makes boost by 3000RPM easily but even though boost (5-8psi right now) holds to 8000RPM, it still feels (according to my butt dyno) like the engine runs out of steam up top. I will know for sure when I get on the dyno.

 

yhea i know but he asked what limits reliable high hp. the fd motors make/take a ton more boost than the renny can (unless you are turblown)

 

Yeah I know, I was just using the example to point out that the Renesis was built for power (in the NA rotary world anyway). The REW should be able to make more boost, it was built with it in mind. But in real life I have learned that a lot of people seem to think the FD was some sort of beast from the factory, when in reality it wasn't in the U.S. In the later years outside of the U.S, that power was bumped up quite a bit.

 

you missed a few

TOO CHEAP OR INSUFFICIENTLY FUNDED

NOT TECHNICALLY UP TO THE CHALLENGE

 

having owned an FD, it was a beast from the factory but was not properly cooled. Light weight and the twin-turbos on an engine built for boosting (ie:lower compression rotors to start) yielded 255 Hp at the crank, and faster throttle response.

The Renesis is Mazda's highest NA compression rotary engine, so boosting it requires care and proper fuel management to last.

 

I am starting a new project soon . From my past experiences I've decided the key things I'll be aiming for are :


Minimising backpressure through turbo selection and good manifold design.
Eliminating cross contamination between rotors .

I'll be aiming for a reliable 400-450whp .

 

I look forward to seeing the results. I for one am not giving up on the Renny yet.

 

I've always had more issues at lower to mid rpms . Passed 6500 doesn't seem to be the main issue .
Also don't forget that max. torque that way is harder on the drivetrain than the smooth torque curve you get with constant boost. Not to mention that you will probably find it harder to drive .

 

If you can get it to 220 without even being on a racetrack , chances are it wouldn't hold out on a track .

 

From what I've seen detonation gets much harder to avoid at higher rpms. Mazda doesn't care about it NA and it may not be a big issue for us either, but it is there and I am making assumptions from that.

Your right the torque will be higher so the transmission will be a bit more stressed. Dunno if it will be an issue yet. The drivability will be determined by how strong/fast the boost comes on which can be managed with the controller. My goals are evolving as I learn more about what the engine can handle.

Any specific problems with high boost at low rpms you're willing to share Brettus?

 

I just have been on several dynos and had det experiences under various conditions and it's always below 6500 . Without actually having the det. earmuffs on myself (at the dyno) I have to say .


18psi at 4500 is a lot of torque - I know Chickenwafer blew his trans in short orderat those numbers. Otherwise broken dowell holes is a possibility but that's only with a det.
P1 injectors need to be larger than stock if boost comes in much below 4000 .

 

Good thread Good to see people pushing the Renesis further vs swaps!

 

You know, it's funny you say that because of the people I know of (not sure if they want me to mention names so I won't) personally who have cracked apex seals under boost it has generally NOT been a WOT, but at lower RPM/high load.

 

People seem to think that by not pushing the throttle to the floor they are somehow saving the engine . The reality is that you only need about 30%throttle to get full load/boost .

 

There is a lot of timing at low RPM. A lot more than most people realize. If you don't have a post IC IAT sensor and you heat soak the intercooler and then downshift you can send a hot slug of air into the engine which is not accounted for in timing, and it could be bad.

The other option is that people are pushing too much timing down low. Again stock timing is pretty aggressive.

I don't see the problems with the engine at low RPM being mechanical in nature. It's too much timing from one source or another. We should be able to overcome that.

Depends on what you mean by 30% throttle. Yes 30% open on the butterfly is going to give you near WOT, but 30% on the pedal will not. If it was that way the throttle would be an on off switch instead of a useful control.

The major exception I see is the Greddy kit's original setup. If you put the boost reference downstream of the throttle then it will keep building pressure until you hit full boost in the manifold or the turbo runs out of push. That's just a bad idea, and leads to over-boost and full load at partial throttle.

Thanks for the info on the P1 injectors. I thought that the P2s would come on due to load, but I am pretty ignorant on injector staging.

I went with a s2 tranny to avoid quick destruction, but your right that is a lot of torque. If it works I may have to look into other transmission options, but I like where things are going right now.

 

I'm talking about the 'accelerator position' parameter on the throttle map . Anything much past 25% and you are close to full boost . On the stock maps that isn't much travel on the pedal . Of course it does depend on how well your turbo spools up as to if that's an issue or not .



Yes that was a problem , as is putting an EBC signal line post TB on a fast spooling turbo.

 

Yeah learning how to press the pedal once you are boosted takes a little getting used to after winding it out for so many years NA.