GTM Performance Engineering Stage 1 Turn key Supercharger kit In house Instal II
06-20-2010, 12:43 AM
#16
I'm saying to keep boost you have to have back-pressure on a supercharger system. On a turbo, the less restriction the better. Plus the proof is in the pudding, look at Shumby's build. Long-tube headers and 2.5" exhaust he couldn't get anymore then 4psi. Why? because the lack of back-pressure. Put the stock exhaust back on, boom made more power at a full 6psi.
06-20-2010, 07:13 AM
#17
It really has nothing at all to do with the exhaust system..... the restrictions of the stock headers, cats and muffler are just a means to an end here. The real problem is intake/exhaust valve overlap. Our engines are designed and tuned to be high output per liter normally aspirated machines. In this situation there is a point in the engines cycle as its transitioning from exhaust stroke to intake stroke where the exhaust valve is closing and the intake valve is opening (both valves open slightly at the same time), this situation causes an increase in volumetric efficiency due to the exiting gases actually pulling the intake charge into the cylinder (think siphoning effect). This gets the intake charge moving earlier in the cycle and in some situations creates a "ram air" effect at certain rpm ranges depending on intake lengths and resonate frequencies.
Now if your super charged, the boost that is being built up behind the closed intake valve in the intake manifold literally blows through the opening intake and out the closing exhaust valve wasting the pressure that was built and lowering the amount of boost potential from the blower.
So it’s not really an exhaust problem, it’s a valve timing problem.
Class dismissed......
Now if your super charged, the boost that is being built up behind the closed intake valve in the intake manifold literally blows through the opening intake and out the closing exhaust valve wasting the pressure that was built and lowering the amount of boost potential from the blower.
So it’s not really an exhaust problem, it’s a valve timing problem.
Class dismissed......
06-20-2010, 07:44 AM
#18
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It really has nothing at all to do with the exhaust system..... the restrictions of the stock headers, cats and muffler are just a means to an end here. The real problem is intake/exhaust valve overlap. Our engines are designed and tuned to be high output per liter normally aspirated machines. In this situation there is a point in the engines cycle as its transitioning from exhaust stroke to intake stroke where the exhaust valve is closing and the intake valve is opening (both valves open slightly at the same time), this situation causes an increase in volumetric efficiency due to the exiting gases actually pulling the intake charge into the cylinder (think siphoning effect). This gets the intake charge moving earlier in the cycle and in some situations creates a "ram air" effect at certain rpm ranges depending on intake lengths and resonate frequencies.
Now if your super charged, the boost that is being built up behind the closed intake valve in the intake manifold literally blows through the opening intake and out the closing exhaust valve wasting the pressure that was built and lowering the amount of boost potential from the blower.
So it’s not really an exhaust problem, it’s a valve timing problem.
Class dismissed......
Now if your super charged, the boost that is being built up behind the closed intake valve in the intake manifold literally blows through the opening intake and out the closing exhaust valve wasting the pressure that was built and lowering the amount of boost potential from the blower.
So it’s not really an exhaust problem, it’s a valve timing problem.
Class dismissed......
06-20-2010, 08:41 AM
#19
I'm saying to keep boost you have to have back-pressure on a supercharger system. On a turbo, the less restriction the better. Plus the proof is in the pudding, look at Shumby's build. Long-tube headers and 2.5" exhaust he couldn't get anymore then 4psi. Why? because the lack of back-pressure. Put the stock exhaust back on, boom made more power at a full 6psi.
06-20-2010, 09:27 AM
#20
Administrator
It really has nothing at all to do with the exhaust system..... the restrictions of the stock headers, cats and muffler are just a means to an end here. The real problem is intake/exhaust valve overlap. Our engines are designed and tuned to be high output per liter normally aspirated machines. In this situation there is a point in the engines cycle as its transitioning from exhaust stroke to intake stroke where the exhaust valve is closing and the intake valve is opening (both valves open slightly at the same time), this situation causes an increase in volumetric efficiency due to the exiting gases actually pulling the intake charge into the cylinder (think siphoning effect). This gets the intake charge moving earlier in the cycle and in some situations creates a "ram air" effect at certain rpm ranges depending on intake lengths and resonate frequencies.
Now if your super charged, the boost that is being built up behind the closed intake valve in the intake manifold literally blows through the opening intake and out the closing exhaust valve wasting the pressure that was built and lowering the amount of boost potential from the blower.
So it’s not really an exhaust problem, it’s a valve timing problem.
Class dismissed......
Now if your super charged, the boost that is being built up behind the closed intake valve in the intake manifold literally blows through the opening intake and out the closing exhaust valve wasting the pressure that was built and lowering the amount of boost potential from the blower.
So it’s not really an exhaust problem, it’s a valve timing problem.
Class dismissed......
That could be why increasing the restriction in the exhaust system would force the boosted air in the chamber during valve overlap, or at least slow it down from escaping?
06-20-2010, 09:41 AM
#22
Registered User
lol
I'm still confused as to why GTM went with two filters and instead of just one large filter and filter-to-SC pipe. It would certainly bring the cost down a little :/
I'm still confused as to why GTM went with two filters and instead of just one large filter and filter-to-SC pipe. It would certainly bring the cost down a little :/
06-20-2010, 09:47 AM
#23
Also, overlap is one of the ways to make big power up high in a n/a engine. At high rpm's the exhaust scavenging effect helps pull the incoming air in. This is at the sacrifice of low rpm manners though, rough idle, low vacuum... Usually you will see a performance cam for a boosted application act very tame on the street vs a performance cam dedicated for n/a.
06-20-2010, 09:53 AM
#24
Also, overlap is one of the ways to make big power up high in a n/a engine. At high rpm's the exhaust scavenging effect helps pull the incoming air in. This is at the sacrifice of low rpm manners though, rough idle, low vacuum... Usually you will see a performance cam for a boosted application act very tame on the street vs a performance cam dedicated for n/a.
06-20-2010, 12:10 PM
#25
Thanks, guys.
Good info. Thanks!
It really has nothing at all to do with the exhaust system..... the restrictions of the stock headers, cats and muffler are just a means to an end here. The real problem is intake/exhaust valve overlap. Our engines are designed and tuned to be high output per liter normally aspirated machines. In this situation there is a point in the engines cycle as its transitioning from exhaust stroke to intake stroke where the exhaust valve is closing and the intake valve is opening (both valves open slightly at the same time), this situation causes an increase in volumetric efficiency due to the exiting gases actually pulling the intake charge into the cylinder (think siphoning effect). This gets the intake charge moving earlier in the cycle and in some situations creates a "ram air" effect at certain rpm ranges depending on intake lengths and resonate frequencies.
Now if your super charged, the boost that is being built up behind the closed intake valve in the intake manifold literally blows through the opening intake and out the closing exhaust valve wasting the pressure that was built and lowering the amount of boost potential from the blower.
So it’s not really an exhaust problem, it’s a valve timing problem.
Class dismissed......
Now if your super charged, the boost that is being built up behind the closed intake valve in the intake manifold literally blows through the opening intake and out the closing exhaust valve wasting the pressure that was built and lowering the amount of boost potential from the blower.
So it’s not really an exhaust problem, it’s a valve timing problem.
Class dismissed......
Last edited by Buddy Revell; 06-20-2010 at 12:15 PM.
06-20-2010, 03:01 PM
#26
Thats where our VVEL system comes in...best of both worlds. This boost issue can be addressed with a little VVEL tuning. But I'm not sure at this point that GTM has the ability to do so with the software that they are using, or it may be just a time issue and they havent gotten around to tuning the VVEL system to optimise a free flowing exhaust system.
06-20-2010, 03:03 PM
#27
Mikelr has some of the info you need in the post below yours. I know what you are saying and I'm not trying to be mean or a jerk, but what you are saying is wrong. What they said the problem was with Shumby's car was wrong. We've discussed this a little more on the other sites.
06-20-2010, 05:26 PM
#29
Thats where our VVEL system comes in...best of both worlds. This boost issue can be addressed with a little VVEL tuning. But I'm not sure at this point that GTM has the ability to do so with the software that they are using, or it may be just a time issue and they havent gotten around to tuning the VVEL system to optimise a free flowing exhaust system.
06-20-2010, 06:03 PM
#30
Yes and no. The VVEL can only change the intake valve lift which just slightly effects overlap. If it could change the LSA then we would be talking something special. The new Viper's V-10 is able to adjust the LSA with their new CamInCam. They are able to move the exhaust lobes throughout the RPM range. Higher LSA down low and a lower LSA up high.
I hope GTM works something out, I'm waiting on my SC kit and I'm running Stillen headers and Berk cats....