New Exhaust System Advice

[sfwilliams@comcast.net (Scott F. Williams)]

> There is an ideal amount of back pressure for every motor.

That is correct, Dave. Zero is ideal, but negative is better. -always.

> Too much is restrictive

Correct.

> and not enough messes with the vacuum effect or swirl or
> something but causes a reduction in power also.

Incorrect. :^)

> ...if it's just an N/A motor then there is an ideal amount you
> just gotta find it.

So, what you're saying is that if you have a completely open exhaust with
10" exhaust pipes, but stick the optimally-sized potatoe in the end...
you'll have a tuned exhaust? No way, there's more to it than that. The fact
of the matter is that exhaust gas velocity (EGV) often suffers when you open
up the exhaust too much. The backpressure may drop to zero and that would
create a gain in power. However, the reduction of EGV decreases the
scavenging (evacuation of gasses from the combustion chamber) which, in
turn, reduces the output lots more than the amount by which the reduction in
backpressure increases it.

*That* is why running too big of an exhaust often decreases power. In and of
itself, the reduction in backpressure is *always* a good thing. However, you
have to do it the right way in order to produce net gains. Put another way,
if you could both increase the EGV and simultaneously reduce the
backpressure to zero, you'd have bigger gains than if you increased the EGV
but kept the backpressure the same.

backpressure <-- "BAD!" :^)
--
Scott F. Williams
NJ Scirocco nut
'99 Subaru Impreza 2.5 RS
Mazda 323 GTX turbo "assaulted" vehicle
Golf GTI 16v "rollycar"
ClubVAC: "Roads found. Drivers wanted."