The 450whp Renesis engine - why it will never happen - theory
 

As many of you know , I've been pursuing the goal of creating the highest whp Renesis ever recorded . I believe I have succeeded in doing that (arguably) but along the way have encountered many engine failures. Each failure, while devastating for me, has made me think about "why is this so hard?" . I have had a few theories along the way and attempted to solve the issues I saw . One being the reversion created within the siamese exhaust port area . While I still believe this happens and is a negative ...... I now think I have worked out what the real issue is. Up till now most engine tuners/builders have gone with the 'exhaust port size is too small' theory. I say ...port size is perfectly adequate . The issue is actually exhaust port closure timing. I will attempt to explain :

Here we have the exhaust port about to begin closing .
Note a few things here
1/There is still a ton of exhaust gas left in the chamber. In a boosted engine the pressure will be more than double what it would be in an N/A engine.
2/The tip of the rotor (where the arrow is ) is the furthest part of the rotor from where the teeth are engaging with the stationary gear. This means that tip is at a point where it is moving faster than any other point on the rotor.
3/From this point on wards ,while the exhaust port is closing , the rotor face closing the port is moving at near it's fastest possible rate . What this means is that the port closes VERY quickly.
4/KEY POINT :The area of the exhaust port reduces so rapidly that it's ability to expel the remaining gas can , in a boosted engine, reach a point where it just can't finish the job . This leads to an extremely high pressure remaining within the chamber through to the next phase .

https://cimg9.ibsrv.net/gimg/www.rx8...e096fa8da8.jpg

Now take a look at the rotor position just as the exhaust port fully closes.
Note:
1/The rotor has now reached top dead center for the exhaust phase of the cycle. Up until this point the rotor face has constantly been compressing the exhaust gas to expel it from the chamber .
2/Any remaining exhaust gas is automatically carried over to the next cycle.

https://cimg0.ibsrv.net/gimg/www.rx8...66fe5ade57.jpg

Now have a look at a peripheral exhaust port engine as used in earlier rotaries . Exhaust port about to begin closing.
Note
1/Compare the amount of exhaust gas left in the chamber with the first pic. above .
2/The rotor has already gone PAST exhaust top dead center and is only now about to close . Meaning the exhaust port is FULLY open during the entire period that a Renesis exhaust port is rapidly closing and is fully open for the entire period before it reaches top dead center.
3/By allowing the exhaust port to be fully open for so long , the power potential for this engine is massive, as has been proven over the years.
https://cimg5.ibsrv.net/gimg/www.rx8...15d8fb9c93.jpg

Edit 29/082020 : I only recently came to the realisation that there may also be a major issue with the Siamese port . That being that around the 400 mark , I believe this port becomes totally flow choked. As in , it will just not carry any more flow whatsoever. What this does is direct any extra flow to the outer ports, exacerbating the issues already mentioned above.

Summary:
EDITED
My previous statement was that there was a horsepower ceiling of 450ish WHP. It has been proven that with a turbo big enough along with other changes this is not the case. Higher whp is indeed possible, but requires making some extreme choices that make the engine impractical for most situations.

Now while your extensive work put into the Renesis arguably supports this claim, I would like if possible if you could clarify something for readers who are aiming at increasing power output of the Renesis.

Overall would you say to someone looking to increase power to do so with the Renesis, or to swap the motor out for an engine such as 13b-re or 13b-rew?

And does your response also apply for those whom are aiming for a much lower and more modest, factory like power output of around 260-300 whp? What would you say for those individuals?

I believe if anyone is qualified to answer those questions, it would be you.

4 port same situation ? What did Pac Performance end up making in the end ?

If you want over 400 - there is no debate

As long as it's done well with consideration for the high compression ratio ... the Renesis is fine at those power levels.

Yes ---same for 4 port .
It's rumored Pac made 427whp but I can't recall ever seeing a dyno . Again ... be aware that , for example 430whp on a dynojet is only 385ish on a more realistic dyno.

You did a good job explaining it.

Combined with the fact Renesis was made with emissions(where more recycled unburnt gas and no intake/exhaust port overlap are good) in mind, this doesn't really surprise me.

https://cimg5.ibsrv.net/gimg/www.rx8...6d87289953.jpg
Found this. On E85 ?

Ah ok ... Probably was E85 .

So, a hybrid SP/PP setup would be required to help with exhaust gas expulsion?

This is awesome Brettus. Thank you. So what could be done?
One obvious/naive solution would seem to be to rev lower so the pressures in the chamber and beyond the exhaust port has more time to equalize, then run more boost. You'll have to redo the intake design but if you're running boost, who cares?;)

Hence the 4-port question, I imagine...

Brettus, have you measured exhaust pressures and EGTs? Might give some insights depending how the numbers trend as boost is added.

It'd be destructive to the housing, but a pressure transducer clocked to the exhaust port centerline of the housing would also give insights into what exactly is happening. If the pressure wave is still strong when the port closes, we'd see a spike in the housing as the volume is briefly compressed before the intake port opening is exposed.

Tuning equipment, dyno time, and turbo fabrication aside, has the actual engine cost been extensive for you? You noted several failures -- were they housing-damaging failures, or were they such that you were able to get back to action with just new seals?

IMO ... yes . But I would be blocking the side ports off completely as they would only mess up turbo response . And once a PP is there , there is no need for more exhaust port.

Yes reving lower and adding more boost would appear to be a solution .... However , over time , as my setup got more and more efficient , the "ceiling" point was reached at a lower and lower rpm . So I think you would end up with similar power but a heap more torque.

Yes , have been watching both of those all along . I spent a lot of effort in reducing turbine pressure but it never did much for peak power as you would expect. I believe due to the port timing issue as explained above.


Well ................. It's been an interesting hobby for me. I would say it's been expensive but I could have picked other hobbies that cost me a ton more too :) . Failures generally result in a stuffed housing and possibly an iron or a rotor. Each failure has cost me between $2500 and $5000. I've learnt that a bad detonation will do damage to something no matter how you build the engine. If you go with bendy apex seals and they don't break ....you end up distorting the rotor and breaking a corner seal which can do just as much damage .

What about getting a set of plates milled to match the intake ports and block the exhaust ports? Giving you mill the iorns to accept them. Could you then open the standard side ports to the water jacket and have a external coolant manifold. That way you can utilize some cooling in the area to help prevent warping of the plates? I imagine I am over looking an obvious flaw in the idea.

The 12a housings could be used or add a exhaust p-ports to a renesis.

Don't understand what you are suggesting ?

https://cimg5.ibsrv.net/gimg/www.rx8...11efdaae25.jpg
the insert done similar to the one I screen shot. To keep the stock intake ports. I am thinking you could then run p-port exhaust. In just covering up the side exhaust ports it would create a hit spot that would warp. So open the side exhaust ports into the coolant jacket so coolant could flow along the back side of the plate in that area. Leading to needing a way to contain the coolant trying to exit the iorns where the oe manifold was. If someone took a flange and built something for the coolant to flow though to close it back in to the system.
I wish I knew more on how the coolant flows through the engine without knowing that I think my idea is dead in the process.
Thanks for giving us a realistic cap on power before it starts to sound like a jar of marbles in a hyper child's hands.

Got ya ! Yeah something like that would be great if you could seal it all up etc.

Assuming this theory is correct, we would expect to see max power improvements from exhaust porting that extends the exhaust port opening by a few more degrees of rotation. Does anyone know if extending exhaust ports has shown to improve max power on a turbo renesis?

Additional to the above "port closing early" theory, the momentum of the gas as it flows in and out of the engine also impacts efficiency. When you compare the gas flow out of a side port vs a peripheral port, the peripheral port doesn't require the exhaust gas to change direction as it exits the chamber into the port - the opening is right in front of the rotating rotor face, so it's a natural path for the exhaust gas to take. Compare this with the side port, where the exhaust gas needs to take a sharp right angle turn to leave the chamber. I would expect this also has a significant effect on the engine's ability to breath, particularly at higher rpm.

Yes ...I have found a way to do this and tried it . The extra porting was very small however plus my engine builder decided to 'upgrade' my mod without asking me and messed up the way it worked . End result was ...it did nothing I could notice. Key thing with doing this is not to inadvertently allow exhaust gas from the next cycle , which is at a much higher pressure, access to the chamber you are trying to evacuate .

ya bunch of newbs are over thinking this. a turdblown turbo kit gets ya 500whp out of the box lol

Too bad they don't offer Renesis plates with the exhaust ports deleted...

Aluminum Front Side Housing for 86-95 Engines - Racing Beat

Great idea ....wonder if there would be a demand ..............

Just to add to this ...I looked up Dynapack dynos and found they are even more optimistic than Dynojets .
Pretty sure they used a 4 port for this and yes it was probably on E85 but realistic whp will be well under 400. Note also how low the rpm was at peak power (which is what we were discussing earlier) and how poor the turbo response is ...meaning it made a lot of torque but had a very narrow power band - similar to Turblowns' effort with the EFR9174.

Yes it was a 4 port with Auto
Can't find any updates after 2013