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Trying to bend my mind around a couple statements I've read here and elsewhere...

1) if it actually does happen, how does reducing backpressure result in a loss of power?

2) how is it an exhaust system can give increased torque at low rpm, when there really isn't a lot of exhaust to move, and no increase at the top end, where the exhaust volume peaks?

thanks
 

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nonsensez9 said:
Trying to bend my mind around a couple statements I've read here and elsewhere...

1) if it actually does happen, how does reducing backpressure result in a loss of power?

2) how is it an exhaust system can give increased torque at low rpm, when there really isn't a lot of exhaust to move, and no increase at the top end, where the exhaust volume peaks?

thanks
I have not heard about a loss of power... I know that with the MC I used to drag we lost power by going with straight pipes... You had to redo the intake, pistons etc. to work with that an open system... but there you have swirwling motions etc...

I'd guess that at low rpm it is easier for the engine to push the exhaust through a more open system, hence driving more power to the drivetrain instead of pushing exhaust...?? On that same effect when it's all flowing it just moves and the gains are smaller, especially with an X but also with an H that makes some suction helping on the way...??

Just my .02 Cents...
 

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nonsensez9 said:
Trying to bend my mind around a couple statements I've read here and elsewhere...

1) if it actually does happen, how does reducing backpressure result in a loss of power?
Generally speaking, you have altered the engines effiency at low pumping speeds. With properly sized exhuast, software tuning can recover most of it back and sometimes more. See #2


nonsensez9 said:
2) how is it an exhaust system can give increased torque at low rpm, when there really isn't a lot of exhaust to move, and no increase at the top end, where the exhaust volume peaks? thanks
Exhuast system works the same way the intake does, tuning. Header sizing is dependant on exhuast valve and port size. Once primary size has been determined, header length can be adjusted to 'shift' the curve around the peak flow to maximize either the bottom end or top end.

It's all about speed. Air speed. Exhuast gases can move at an average speed of 350 ft/sec. The "pressure wave" or pulse moves at the speed of sound. This is the 'sound' you hear in the exhuast. Tuning these two is what headers are all about. The gases cool, they slow down, they expand. When and where, is what headers are all about. The exhuast sytem is an extension of this. When changing exhuast pipe sizes effects the output, something is not right back up front. But then, it's all a compromise.

Basically, when looking at flow either into or out of an engine, remember than air is a liquid. By watching how a water stream flows and reacts to obstructions or direction changes, and how current speed changes as the stream narrows and widens, you'll have an idea of how the air reacts in and out of an engine.
 
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