The reason I ask is. I have Mac headers and y-pipe, Mac Off road pipe, then borla catback with the restrictor out. I hooked up a boost gauge and I didnt see any boost until almost 5,000 rpms , I then installed a random tech hi-flow cat, and now my full boost comes in at around 3,000 rpms. Why would a centrifical supercharger need backpressure?? thanks for any replys.

 

They don't need back pressure. Backpressure has absolutely nothing to do with the belt turning the supercharger. Maybe your experiencing belt slippage. The supercharger impeller speed is directly related to engine RPM, not backpressure. You need to look elsewhere.

 

Thats what I thought...the thing is, that I ran the tests back to back with the same boost gauge. I drove it with a cat, then came back put the ORP in and retested. I know that when you port your heads you loose a little boost, so maybe this has the same effect???

 

I don't see how that's possible... an s/c is completely isolated from the exhaust system. It builds positive pressure in the intake manifold so that once that valve open all that air is smashed in. The only backpressure is the pressure that forms between the combustion chambers and the blower. Putting an ORP would have no effect on boost and when it came in, that SHOULD be consistent unless the weather is drastically different, it must be some other problem you are having.

 

Yeah, you need to check something else. I have Mac headers, Y-pipe and off road pipe and see boost around 3K

 

Yea... I try never to floor it under 3K anyway because the load is a lot higher on the engine (when drag racing you are never under 3k) but I have tried it before and I will start boosting at just 2.5-3k. But I start making some usable boost at like 3.5K and then max boost at 5.5K and up... it's something else.