Backpressure, again, for the n00bs

[95ProLeila]

alright, for all the recent stupid idiot talk about backpressure being good, I refer you here:

http://www.wihandyman.com/forum/showthread.php?t=620&highlight=backpressure

Please stop saying n/a needs backpressure, it doesn't. End of story.

[Vash00es]

Go ahead and burn your valves to **** with no backpressure then

[goldstar]

Go ahead and burn your valves to **** with no backpressure then

That belief is a myth. Pure racing engines such as used in Formula I and Indy cars have exhaust systems with little or no backpressure and they certainly don't burn their valves as a consequence. The goal is to obtain maximum exhaust gas extraction by utilizing a pipe diameter that maintains sufficient gas velocity to thoroughly scavenge the cylinders. The optimum pipe diameter is determined by testing: too small and it creates unwanted backpressure that interferes with good scavenging (and incidently, raises exhaust valve temperature-the opposite of your contention); too large and the resultant loss in gas velocity also provides less than maximal scavenging. Of course, in a racing engine the RPM band in which maximum scavenging occurs is very narrow whereas in a sporty road car, the goal is to achieve relatively good scavenging over a much wider power band. However, the principal is the same.

Reference:
Scientific Design of Exhaust and Intake Systems, 3rd edition, by Philip H. Smith and John C. Morrison

[95ProLeila]

pwned. Basically, people don't understand that backpressure isn't the only variable. Velocity is what you're going for, which is inversely related to backpressure. People think that when they put a 4" exhaust on their 4 cylinder and their power goes to ****, that it must be because they don't have backpressure, it couldn't possibly be because they're a dumb**** and killed all their gas velocity . . . .

[Vash00es]

it happens

[Kevin]

this topic was dispelled and mitigated over 2 years ago through these forums.. if not way before i got onto the topic.. no new information..but as a matter of restating.. can't hurt.
kevin