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Great idea ....wonder if there would be a demand ..............
Going to go out on a limb and say probably not...or at least not enough to justify development of the castings.
These might also be interesting as they can likely just machine a set. Billet Inc. ? Home of the Worlds Fastest Rotary Engines Though the Billet housings with the Racing Beat wear coating (instead of the replaceable wear surface) sounds intriguing.
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 .
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From the comparison of port area to crank angle the speed that the port is closing doesn't appear to be that fast. the peripheral port opens and closes faster. So there is defiantly a limitation of volumetric efficiency of side ports but is it due to the speed at which it is closing?
From the comparison of port area to crank angle the speed that the port is closing doesn't appear to be that fast. the peripheral port opens and closes faster. So there is defiantly a limitation of volumetric efficiency of side ports but is it due to the speed at which it is closing?
That's not a very good representation of reality IMO. Renesis has a long period where it's area is constant (which should be represented by a flat line ) just like the PP does. Plus the actual crank angle closing degrees is not that much more.
The key difference between the PP and the Renesis isn't so much the speed of closing ...it's the timing of the closing .
But ........... if the Renesis was able to remain fully open for longer but retained the same fully closed timing ...somehow ..... we would have a much higher power ceiling.
That's not a very good representation of reality IMO. Renesis has a long period where it's area is constant (which should be represented by a flat line ) just like the PP does. Plus the actual crank angle closing degrees is around about the same.
The key difference between the PP and the Renesis isn't so much the speed of closing ...it's the timing of the closing .
But ........... if the Renesis didn't close as fast as it does yet retained the same timing ..... we would have a much higher power ceiling.
I wonder if this data was from a pre-production engine. animations indicate there should be a small flat area but in terms of crank rotation it is small.
Here is the chart in the Renesis PDF . It's more accurate than the one you posted but I still feel it doesn't properly represent that last few degrees of closing .
Anyway ...it does still illustrate my point . Look at the cross hatched area ... works ok for an NA engine , but double the amount of air to expel and that x-hatched area makes all the difference in getting rid of the last of it.
The extra port area earlier will do a good job of dumping the initial charge for lower flow situations but as pointed out earlier, even though port area is greater ......it's still got a really poor exit from the chamber . Also remember that 1/2 of that port area exits through the siamese sleeve . Hold up a siamese sleeve next to a peripheral port and you realise what a joke it is.
Even with extra port area ....my guess is that it doesn't get the gas out as fast as a PP does ....even when fully open .
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...
I might have been a bit hasty ...... been giving this a lot of thought and analysing old logs at various boost pressures. I have been reducing rpm over time but perhaps not by quite enough . It may be possible that we can extract quite a bit more power with this approach.
One thing I am pretty sure about is that ...once the power curve on a Renesis starts heading down , the reason is failure to extract exhaust gas. So perhaps the answer is never let a high hp engine go past it's peak power...............
Nice! Also if you're narrowing the rev / flow range, you choice of turbos opens up?
For peak power ... you still need the same (if not more) airflow if you reduce rpm but at a higher boost. This does suit typical compressor maps better as most maps are more efficient at higher flow/boost than where we typically run the Renesis.
Here is the chart in the Renesis PDF . It's more accurate than the one you posted but I still feel it doesn't properly represent that last few degrees of closing .
Anyway ...it does still illustrate my point . Look at the cross hatched area ... works ok for an NA engine , but double the amount of air to expel and that x-hatched area makes all the difference in getting rid of the last of it.
Do you know which 13B port design Mazda compared here? A 4-port REW, 4-port 13B-RE, 4-port 13B-DEI (TII), or one of the 6-port naturally-aspirated 13B's from the DEI era?
Do you know which 13B port design Mazda compared here? A 4-port REW, 4-port 13B-RE, 4-port 13B-DEI (TII), or one of the 6-port naturally-aspirated 13B's from the DEI era?
Don't know. I think they were just trying to make the Renesis look good . The basic concept being ............bigger ports all around, applies to any of those earlier engines in varying degrees.
It would be interesting to see what peak numbers a MSP could produce with a large top-mounted turbo and E-85/race gas. While it would be a lag monster, maybe the lower boost and back pressure would help keep the motor together? Would the exhaust ports just choke it up? Anyone tried this?
That is essentially what Turblown did with the lucky7 car.
9174 running E85 made 422 on a dynojet . I believe they are now trying a 9180 .
So yeah ...very laggy and no more top end than I made ... BUT........... promising signs in the 6-7000rpm rev range which supports what Loki and I were just discussing.
What interests me is the way power doesn't climb but stays relatively level 6000-8000 .Boost does drop but only by 2psi . In any other engine we would expect power to rise to a peak then drop away .
I notice that nobody ever takes a turbo MSP engine out to 9,000 RPMs, which seems to be that the smaller low-mount turbos are moving way outside of their efficiency. In the dyno chart above horsepower was pretty flat as you mentioned, and the power appeared to fall with the boost pressure. It would be nice to see what would happen from 8,200-9,000. Even a laggy turbo with a 3,500 RPM (5500-9000) powerband would be a monster in a straightaway.
I notice that nobody ever takes a turbo MSP engine out to 9,000 RPMs, which seems to be that the smaller low-mount turbos are moving way outside of their efficiency. In the dyno chart above horsepower was pretty flat as you mentioned, and the power appeared to fall with the boost pressure. It would be nice to see what would happen from 8,200-9,000. Even a laggy turbo with a 3,500 RPM (5500-9000) powerband would be a monster in a straightaway.
I wonder .............just looking at the dyno .......... if they didn't even open the APV ! The earlier dyno they did shows a definite hump then a hollow right after the APV would open ..........the above dyno doesn't . It actually looks like they got a better power curve by doing that ! Actually .......... they added a bridgeport to that engine as well ............. which would have helped with flow if they had deleted the APV ...makes sense !
Power just drops sharply away after 8000 ....... that's if you haven't blown the engine.
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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.
Originally Posted by Brettus
The extra port area earlier will do a good job of dumping the initial charge for lower flow situations but as pointed out earlier, even though port area is greater ......it's still got a really poor exit from the chamber . Also remember that 1/2 of that port area exits through the siamese sleeve . Hold up a siamese sleeve next to a peripheral port and you realise what a joke it is.
Even with extra port area ....my guess is that it doesn't get the gas out as fast as a PP does ....even when fully open .
I believe you'll are on to something here... IMO based just on the dynamics of exhaust gas expulsion between the PP vs. the Rene, I'd suspect to find "some indications" by mapping not only exhaust "open area", but also pressure profile against shaft angle as well. The PP and Rene both expel gas initially by the pressure created by the rapidly decreasing chamber volume. But dynamics drastically change in the final degrees of closing. The PP gets an extra "boost" so to speak b/c the rotor face itself acts as a hammer to "press" the gas out of the exhaust port. Conversely, not only does the Rene not experience this phenomena...while the PP port is experiencing the "hammer" in its final closing, the Rene experiences a) decreasing exhaust pressureas its diminishing exhaust port areas "scissor" closed, b) a circuitous route (JB), and c) 2 of 4 ports exiting to the Siamese runner (Brett). Impossible to remedy w/side exhaust ports. I think Brett via experimentation has h/d a good job discovering the boundary of the Rene's ~ max HP d/t the exhaust expulsion constraints.
Bottom line... the PP is simply the more elegant, and efficient design for power.
I love how everyone compares the RX-8 to the FD RX-7, fully ignoring the fact that:
- RX-8 is a lot cheaper than FD(FD was almost as expensive as a Corvette from the same time period), and in general targets a lower market
- RX-8 has to face stricter emission standards
- FD was designed during Japan's bubble economy. That was a time where some of the best Japanese sports cars were made, because the Japanese manufacturers weren't concerned about what they should make, but rather what they can make.
IMO comparing the RX-8 and FD is about as reasonable as comparing a Corvette and a V6 Camaro. Made by the same company, a similar engine, so fair comparison, right?
11-22-2018, 08:40 AM
