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From: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
>
>About your friend and his Cobra's, if you let the gas out freely, you are
bound to get less power from your engine, since the valve timing is designed
for a certain amount of backpressure on the exhaust, otherwise you let out
part of the unburnt mixture, thus letting some of the ponies run away. >
I would offer that this is a generalized statement that may appear true in
some cases but backpressure from a muffler system shouldn't be counted on to
add power. What you may be refering to is the matching of exhaust velocity
with the cam timing. The inherent backpressure that comes with different ID
of pipes does have an effect. High velocity smaller ID pipes will choke an
engine at high rpms but offer great mid range because of better
scavenging....the size of pipe and cam lift / overlap required depends on
what you rpm range you are designing the engine's peak hp and torque for.
Think short fat pipes for high rpm and small long pipes for low end
grunt...for the Max, either will benefit from a muffler able to flow at over
300 cfm with a backpressure of no more than 0.2 psi.
I suspect the Cobras slip-ons flow less than the stock mufflers...so you
have small stock head pipes and a restrictive exhaust. Once the engine
starts to really need to flow the system chokes ...hence the drop in power
everywhere but very low rpm's.
cheers, Terry
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