vpdood said:
ok long extractors good, short extractors bad. are their sizes (width) at all or are they all in length??
Width also matters
, because a smaller pipe generates more suction. When the gas from one cylinder is leaving the pipe into the collector it's motion causes suction in the other pipes and that helps removes gas from them but also helps bring the inlet charge into the cylinder on the overlap of the cam (when both intake and exhaust valves are open) So you should have extractors that suit your cam. Anyway the smaller the pipe the more suction you make and the more power you make BUT too small a pipe doesn't flow enough gas and you loose power so you need a compromise, 1 5/8 of an inch is probably best for a street motor even 1 1/2 inch for really low end torque. But top end racing V8's will run 1 3/4 pipe or bigger. The length of the pipe is important because it times when all the pulses going back and forth in the exhaust come back into the engine and the have to be tuned to the cam, stock cams need much longer pipes than race cams. The same kind of thing happens in inlet manifolds, in a perfect world the inlet runners on your V6 would be more than twice the length that they are, for the sound waves to help ram air into the cylinders but Holden don't want to be making tunnel rams or manifolds with long runners and a throttle body on each side if the engine because it costs too much and bonnet scoops aren't cool on factory cars : ). Well later on they have tried to make long runners on some engines, you can see it on the Holden EFI V8 and I think the Ecotech has a similar setup with the tuned length runners bending over the top of the manifold. If done well good long runners could add so much extra torque that in theory would knock around half a second off the quarter mile time of a stock V6 commodore. The only easy way I can think to make such a manifold is get a stock one, cut all the top off it back to where the runners join the manifold, then just weld on new straight runners that come straight off the head ports and out over the towards the top of the heads, then a new plenum and a throttle body on each side, similar to the old weber setups on some racing Chev V8's. I'm not sure how you would be able to run the IAC valve on both throttle bodies, or if that would still be possible, you might have to just block one side up and hope the car still runs ok with only one side having the sensors working and the pedal might be a bit stiff pushing both springs :0.
I don't know if you have ever used software like engine analyzer but it calculates all these kind of things to within a few horsepower and if you play around with it you can come up with a combination of inlet and exhaust that will get a VN commdore with all stock engine internals down the quarter mile in under 15 seconds (with time to spare). Anyway that's a basic idea of what goes on, I'm no expert myself (just read alot of books over the years : ))
