We need to clear some misinformation up as I have seen in in a couple of threads as of late:
Quote:
Originally Posted by puretone
just remember, our engines flow gas like a bat outta hell, so yeah bigger runners would help, just so long as you put some sort of back pressure on the exhaust.
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There is an optimum pipe size, bigger is not always better. A smaller diameter will increase velocity. Velocity is a consideration in scavenging in a tuned exhaust. You may be confusing scavenging with backpressure.
Back pressure is
resistance to exhaust flow.
It is an increase in the load that the piston must overcome on the upstroke. It is a force resisting the movement of the piston. It means energy is being wasted pushing the exhaust gasses out, which could have been used to turn the wheels.
It is also an interference with smooth flow of the fresh charge on the intake stroke. The more back pressure, the less fresh A/F charge that can be ingested. Back pressure reduces the engine's VE.
Back pressure is bad!
The optimum level of back pressure is zero. Remember that an engine is a pump. Any thing that restricts the flow through the pump lowers its perfromance.
- Joe