Reply to "me agene! (Question regarding Pantera headers)"

> Just remember that an engine is baically a pump and all pumps need a little
> back pressure.

That myth dies hard. First of all, the atmosphere provides back pressure all
by itself. Second, back pressure is not beneficial to exhaust flow. What may
appear as a static back pressure increase may in fact actually decrease dynamic
back pressure. This results in higher flow not due to an increase in back
pressure but due to better scavenging via pressure and sonic wave reflections.
Vizard does a good analysis of how various muffler types appear to the
collector in the May 2005 issue of Popular Hot Rodding. "Exhaust Science
Demystified".

Some engine combinations are more sensitive to exhaust systems than others.
In particular, cams with narrow lobe centers need a very good exhaust system
to work properly. Big port heads like 4V Clevelands tend to work best with
narrow lobe centers. The typical 10.5:1 compression ratio 351C-4V works
best with a lobe center of around 107 degrees. That requires a good exhaust
system.

> The correct answer of course is that the correct "size" of your exhaust system
> will be dependent upon the power output of the motor.

The article I referenced above gives the best design equations for exhaust
system sizing I've seen. They are based upon what your exhaust port flows
at peak cam lift at 28" H20. I use those equations as a starting point for
Dynomation simulations and it's usually pretty close. FWIW, some of the
other published equations aren't even close.

> Increasing the size of the tubing alone is not enough however, the oem
> mufflers are themselves a significant restriction.

Restricitive mufflers can kill most of the gain from good headers.

> The headers sold by Pat Mical at Future Auto have recieved repeated praise
> here on the DTBB.

Pat's headers sacrifice primary length for collector length. Given the
space limitations in a Pantera that's probabaly a pretty decent trade-off.
He also uses the 3" collector diameter so he can run 3" intermediate pipe
and large bore mufflers. May not make much difference on a mild engine
but on a big inch stroker, should be worth a fair bit.

Dan Jones