Quote:
Originally Posted by msumr282
We need to clear some misinformation up as I have seen in in a couple of threads as of late:
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
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okay good, correct my 'backpressure' with scavenging....i did note that when i ran 2.5" free flowing exhaust piping that my power went way down, then added a straight-thru (but swirled) resonator about 3 feet from the exhaust ports that i got a huge increase in power.....then off to the muffler, again a 2.5" inlet which again aided the whole mess of power. Point being that running NA you need this scavenging to a certain degree....going 2.5" and then along the way reducing to 2.25" might happen to help as well....just that my flexpipe had 2.5" coming off of it so i decided to continue with the 2.5" all the way to the back...
resonator & muffler from Vibrant Performance btw, i recommend that!