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.

 

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......

 

Great description, you on right on the money. Vehicles with older valvetrain technology have alot less valve overlap and actually benefit from less exhaust restrictions with a supercharger (viper, mustang, etc...) Not to mention if they had a problem, they could just throw in some new cams.

 

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.

 

I've been looking for an explanation for this, thanks for the write up

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?

 

Thats exactly what is happening grasshopper.....

 

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 :/

 

It doesn't force the boosted (fresh) air in, it just restricts the exhaust (bad air) from going out. This makes your boost number go up but that doesn't guaranty power will go up. I'll try and link a picture of a top fuel engine below. Notice how there is no chance of "restriction" in there exhaust and they are running 45 pounds of boost.

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.

 

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.

 

Thanks, guys.

Good info. Thanks!

 

Thanks for the explanation earlier. They do not have the ability of tuning the VVEL cam timing yet so that equation is out. Only air / fuel ratios and ignition timing. Seems like people are stuck between a rock and a hard place at this point.

 

You're not being a jerk. I just wanted to catch up on the forum and see what the issue was. I'm curious to see if the competitor is going to have the same issue (I would assume so).

 

I think with the head room the Vortec blower has over the Rotex they can literally push past this issue with brute force..

 

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.

 

Agreed, but the amount of lift control is so dynamic that you could effectively delay the opening of the intake long enough to correct (or really mask) the issue.
I hope GTM works something out, I'm waiting on my SC kit and I'm running Stillen headers and Berk cats....