Air intake manifold
02-06-2009, 08:50 AM
#52
I'm working on one.
I found that the 70mm distribution plenum of the stock one was restricting airflow at high rpm when boost is above 15psi. The restriction feels exponential with boost, the more boost you run the more you feel the power fall off on the very top end, it appears to be a percent issue. This is new to all because there aren't many people that have ran the Renesis at these boost levels consistently enough to notice.
I verified this by taking boost readings from right behind the throttle and at the LIM. At 21psi(Yes we have been that high
, updates soon) there is a differential pressure of 1psi starting at about 6900rpm creeping up to almost 3psi psi at around 8200rpm. If you think about it boost behind the throttle body doesn't really mater to engine performance, its meant to be a reference for tuning, its boost in the combustion chamber that really matters. So the car effectively feels like it is loosing 3psi on the top end even though the gauge behind the throttle body is reading consistent boost. For those of you with F/I you all know that 3psi is very noticeable. The turbo I am using in the test definitely has enough flow to hold boost on the engine at 9000rpm up to at least 28-30psi so that is not it, plus it is holding the pressure right behind the throttle body, the restriction happens in the upper intake manifold and it happens in the range where all six ports are open which kinda makes sense. A simple cross area analysis showed that the sum of the cross area of all 6 ports is more than the cross area of the intake manifold right behind the throttle body(I don't have the exact numbers right now). Apparently it becomes a restriction above 450whp which makes sense since it wasn't designed for that hp level.
I am working on one which has an effective plenum chamber equaling about 1.4-1.5X engine displacement which is not that huge for a rotary. It is similar in design to what comes stock on the Cosmo engine but with more plenum volume and should yield significant results on the top end.
Again, this is what I found by taking measurements, I am not theorizing or even attempting to explain why it happens, I simply got the info I needed and decided to experiment and see what happens. I will let you know of the results when all is said and done.
I want to clarify that this will probably not help people that are not going to use it to its full extent like N/A cars and low boost applications, instead your losses under 3000rpm might be greater than what you can make up on top. Its just experimental at this stage.
Best regards,
Chris
I found that the 70mm distribution plenum of the stock one was restricting airflow at high rpm when boost is above 15psi. The restriction feels exponential with boost, the more boost you run the more you feel the power fall off on the very top end, it appears to be a percent issue. This is new to all because there aren't many people that have ran the Renesis at these boost levels consistently enough to notice.
I verified this by taking boost readings from right behind the throttle and at the LIM. At 21psi(Yes we have been that high
, updates soon) there is a differential pressure of 1psi starting at about 6900rpm creeping up to almost 3psi psi at around 8200rpm. If you think about it boost behind the throttle body doesn't really mater to engine performance, its meant to be a reference for tuning, its boost in the combustion chamber that really matters. So the car effectively feels like it is loosing 3psi on the top end even though the gauge behind the throttle body is reading consistent boost. For those of you with F/I you all know that 3psi is very noticeable. The turbo I am using in the test definitely has enough flow to hold boost on the engine at 9000rpm up to at least 28-30psi so that is not it, plus it is holding the pressure right behind the throttle body, the restriction happens in the upper intake manifold and it happens in the range where all six ports are open which kinda makes sense. A simple cross area analysis showed that the sum of the cross area of all 6 ports is more than the cross area of the intake manifold right behind the throttle body(I don't have the exact numbers right now). Apparently it becomes a restriction above 450whp which makes sense since it wasn't designed for that hp level.I am working on one which has an effective plenum chamber equaling about 1.4-1.5X engine displacement which is not that huge for a rotary. It is similar in design to what comes stock on the Cosmo engine but with more plenum volume and should yield significant results on the top end.
Again, this is what I found by taking measurements, I am not theorizing or even attempting to explain why it happens, I simply got the info I needed and decided to experiment and see what happens. I will let you know of the results when all is said and done.
I want to clarify that this will probably not help people that are not going to use it to its full extent like N/A cars and low boost applications, instead your losses under 3000rpm might be greater than what you can make up on top. Its just experimental at this stage.
Best regards,
Chris
Last edited by ChrisRX8PR; 02-06-2009 at 08:55 AM.
02-06-2009, 09:21 AM
#53
Registered
About 10 years ago, a local guy here was testing various intake manifolds on his twin turbo bridgeported 13B race engine. He found that for any given intake runner length, a larger plenum chamber gave him more top end and a smaller one gave him less. He ended up using somewhere around a 700 cu in plenum on that car!
02-06-2009, 09:45 AM
#54
About 10 years ago, a local guy here was testing various intake manifolds on his twin turbo bridgeported 13B race engine. He found that for any given intake runner length, a larger plenum chamber gave him more top end and a smaller one gave him less. He ended up using somewhere around a 700 cu in plenum on that car!
I have seen several RX-7 people with strict race cars go as high as 2.5-3.0X displacement but I had never heard of 700cu.in. That is huge, the 13b is 79cu.in, so its like 8 or 9 times displacement. For street everyone seems to like the 1.4-1.8 range. I guess its all a compromise of bottom for top or vice versa.
Chirs
02-06-2009, 10:05 AM
#55
Registered
I know the displacement debate but when it comes to tuning, injector sizing, turbo sizing, or even equating plenum volume, you really need to go off of 2.6L or basically 160 cu in. Even that is actually pretty small.
02-07-2009, 08:55 AM
#56
good info-- i am assuming that the vdi is "disabled" etc during all of this? there is intake work that ca be done even for the low boost guys. na needs to leave it alone EXCEPT for heat shielding and a phenolic gasket.
dude i KNOW yall are running a w/m system with that boost and what the hell are you doing with the exhaust port? Damn!
OD
dude i KNOW yall are running a w/m system with that boost and what the hell are you doing with the exhaust port? Damn!
OD
02-07-2009, 06:34 PM
#61
2 X 780cc Primaries
2 X 1000cc P2's
2 X 1680cc Secondaries
2 X -044 Bosch pumps
The fuel pumps are good for a lot more than where we are at but that gives you an idea of our long term goals...
Best regards,
Chris
02-08-2009, 12:03 PM
#67
Best regards,
Chris
02-08-2009, 12:18 PM
#68
The devil made me do it
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Ok...I think I see what you are saying. For my understanding alone...wouldn't the pressure at detonation be different if the intake pressure is +30psi? The pressure has to go somewhere and to me the only place for it to go is through the exhaust port. So you can only deduce that there will be increased pressure against the Apex Seals during all three parts of the cumbustion process. The fact that you guys designed and made "performance seals" makes me think that you guys recognized this weakness and I am right at least in theory even though I crossed up some words maybe.
02-08-2009, 12:56 PM
#69
Ok...I think I see what you are saying. For my understanding alone...wouldn't the pressure at detonation be different if the intake pressure is +30psi? The pressure has to go somewhere and to me the only place for it to go is through the exhaust port. So you can only deduce that there will be increased pressure against the Apex Seals during all three parts of the cumbustion process. The fact that you guys designed and made "performance seals" makes me think that you guys recognized this weakness and I am right at least in theory even though I crossed up some words maybe.
.I would like to add that although many people broke their cars at 7-9psi on greddy kits at under 300whp we were able to take the stock renesis to 400whp at 16psi simply because no detonation occurred. Detonation is like multiplying the pressure in the combustion chamber 10 fold so if at 7psi the combustion pressure is 1000psi and at 16psi it is 1400psi they both become huge under detonation. Detonation at 7psi is still huge so our main goal was to make seals that would handle the "impact" of detonation better and at the same time be stronger to handle more psi under normal operation.
We will post some runs with the seals on E85 sometime this year to show you what the Renesis is capable off.
Chris
02-08-2009, 01:45 PM
#70
The devil made me do it
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This is not to be confused with the regular detonation experienced with the 8 where temps in the intake chamber are so high they ignite the fuel prior to getting to the combustion chamber. Right?
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