Originally Posted by F.I. Inc.

Re Post so everyone can see this on the most current page!

A must read for all long tube header owners thinking of adding the GTM supercharger kit:

I wanted to chime in real bad on the GTM supercharger thread. But I have bit my tongue and out of respect for Sam and GTM I will do this in my own thread.

There is alot of talk going around that my headers "flow too well" for the HR motor due to the VVEL with the long duration and overlap.

Shumby now is a proud owner of the GTM supercharger kit for his G37 and has removed our headers due to a lack of boost and power with them. I cannot sit here for any longer and let my headers take the abuse for something else that is causing the issue. I feel that it is not a tuning issue. I feel that it is a hardware issue, i.e. the supercharger itself or the kit.

Here is the deal, headers relieve back pressure. By relieving back pressure you will have a PSI drop off (boost). The goal should be to make as a much torque and power on as little boost as possible. This is called "efficiency".

I have never in my life ever, ever, ever, installed a supercharger on a car along with headers and lost power. The only way it is possible is if the supercharger kit is inefficient. This leads me into the next phase of the topic.

I have spoke to Shumby myself over the phone and here is the information I was given:

Tony, we supercharged the car and with the headers installed along with your exhaust it only made 4 psi. Then we put a smaller pulley on it and only picked up 15 horsepower and very little boost. I was never given the boost number I might add and I don't think Shumby was either. Then I was told the headers were removed and stock manifolds along with stock cats were installed. I was told at this point the car made 6-1/2 psi. So then they took the stock cats back off and put the GTM straight test pipes on the car. Same result, the psi dropped back to a very close place to the headers. No doubt, the stock cats are much more restrictive than the long tube headers or even straight test pipes. So now the stock cats were put back on the car and oh but wait, a boost leak was found. But I was told it was minimal. Either way it is force induction and a leak is detrimental to boost and power! So naturally I asked, after the leak was rectified did you put the headers back on the car a dyno it again. The answer was no we did not!

I want to see an 8 psi stock cat, stock manifold number vs. FI long tube header 8 psi number. I would bet the farm that apples compared to apples we would make higher number across the board. If you cannot get the boost back up with the long tube headers than the supercharger itself cannot move enough volume AKA (CFM) or the supercharger kit itself is holding it back. Size of intercooler, tubing size, the way tubing is routed. A good way to see if the intercooler is efficient is to take a psi reading before it as well as after it. If the psi drop off is dramatic after it than the intercooler is not efficient. If the intercooler is efficient than it is most likely the head unit itself. It physically is just too small and cannot support enough volume to feed to motor. Bottom line you then rely on the stock cats to build the boost.

Here is where the problem lyes with that. Boost is heat and the stock cats were never intended to have #1 to have that much velocity forced through them, (especially for extended periods of time). #2 being a ceramic cat they will never hold up to that kind of abuse. Worst case scenario you send the EGT's (exhaust gas temperature) through the roof before the cat and melt it shut. I think it is a poor selling point to tell people, here is my supercharger kit please buy it. Oh by the way you need to keep stock manifolds and stock cats on the car the make the boost and in return make numbers!

If the car needed that much back pressure than explain why naturally aspirated with no air being crammed into the motor how we picked up substantial amounts of torque and also power accross the board! So until I see see an independent dyno done correctly comparing apples to apples than I am not buying the information that is being sold.

This will also be posted on the first page of this headers thread.

Thank you for taking the time to read this. The phone lines are open...

Tony