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so you're suggesting that it doesn't matter in terms of how much power you're making how much pressure it takes to force the exhaust gasses out of the cylinder. It only matters if it effects scavenging or not?
I said nothing of the sort. Please read my posts before quoting me...
Sonic tuning and pressure levels are two VERY different things, you seem to think they are the same. Sonic tuning involves the exhaust length (including all the way to the cylinder) and has VERY little to do with the actual diameter of the exhaust. The sonic pulse takes a certain time to travel a distance, the diameter of the pipe doesn't affect this very much at all (if any).
Sorry man, but I'll argue this to the death. An NA car needs a certain level of pressure in it's exhaust system to keep the gas moving, if the gas slows then it slows the flow of gas through the ENTIRE ENGINE.
Basics... this is just an example, picture it in your mind... seal a piece of hose into a plastic coke bottle and suck like hell... what happens? A low pressure zone (vacuum) is created inside the bottle. Now, if you were to make a hole on the other end of the bottle, you can suck air through. NOW, if you put your hand over the hole (e.g intake valve closed) and without sucking on the hose, lift your hand off the hole for 1 second, then what happens? Shit all... not much moves. Lift your hand off for 1 second while sucking like shit on the hose, and a shitload of air will rush from outside the bottle into it. Following?
Bottle = cylinder, tube = exhaust, hole = intake valve. The first test (no sucking) represents what happens to your intake mixture when the gas in your exhaust is moving slowly. The second (sucking like buggery) represents the gas moving down the pipe VERY quickly. In the first example, there was higher pressure in the cylinder/bottle (close or at atmo) and in the second example, there was a vacuum in the intake/bottle which sucked the mixture (air only, in the example) into the cylinder/bottle.
Here's ANOTHER example to show you how air being slown down in a bigger tube (and if this doesnt explain it i'm going to bloody well give up) actually creates backpressure... blow into the end of a garden hose and feel how fast the air comes out the end... blow into a piece of 3" pipe and
you will require MUCH more effort to get it to move at the same speed ... why is this? Because when you blow into the garden hose, there is less stationary air for you to blow down the tube... whereas you need to move more air in a 3" tube to get the same results...
in short, there is more resistance to the efficiently fast flow of gas in the BIGGER tube than there is in the smaller tube, in otherwords, MORE backpressure.Does that make it a bit clearer? I know these theories like my own nutsack.... as I said, I've spent a couple of thousand hours at the track testing the theories of exhaust size and sonic tuning... in road cars it's not usually set up very well but in a 14hp go-kart every TINY bit helps.
If you like, I can try to get some dyno time and actually prove these. I would need a GSL cordia donated for a couple of hours though... preferably with a stock exhaust. If that can be arranged, I should be able to get numbers with a stock exhaust, 2.25 (my current one) and a 3" (I'm buying a 3" soon, we could use that) and I reckon I could get it done for nothing... that's assuming a GSR exhaust will fit a GSL and I can sweet-talk the boys into letting me go wild on the dyno for a day
JAPRCR - Yep, turbos
are different... I'm rambling about NA motors, I don't really have any experience with turbo exhausts but I DO believe in 'bigger is better' on a turbo car, to a point... while I think there is such a thing as too big on a turbo car, I highly doubt you could fit it under a cordia
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If it's on a naturally apserated mirage, 2" with press bends should be fine.
Resonator in the middle and a big chrome cannon on the back for pimping.
Sounds like a plan to me
Astaroth.