On Wed, 28 Apr 2004 13:49:41 +0000, Jay Honeck wrote:

Yep, they're ugly -- but I assume they are "tuned" exhausts...

Well, it may not equate, but the tuning on automotive systems is done in
the header.
The length and bends of the pipes from the heads to the collectors is
important, but
the length of the exhaust pipes is not.

Hmmm. I thought that new "performance exhaust" system for Cherokees and
Skyhawks had to be "x" number of inches (feet?) long in order to "tune" the
exhaust, in order to increase horsepower "x" percent?

Isn't that why those things are so big, honkin' ugly, hanging out the bottom
of the plane?

Well, I can't speak specifically to planes in this regard, but for
some other engines, that's the difference between turned exhaust and a
tuned pipe. The idea is that the pipe is used to improve scavenging
capabilities of the engine. Tuned pipes can often be used in
conjunction with performance headers (tuned exhaust) to improve
overall performance of the engine. The length and size of the pipe
directly relates to the targeted RPM range at which the improved behavior
is desired.

Headers are normally used to improve the ability of the engine to get
exhaust out of the engine. Likewise, pipes are normally used to effect
the scavenging abilities (helping to suck exhaust out of the engine). As
you can see, the two can be considered complimentary.

Granted, I don't normally associate pipes with 4-cycle engines. That
ignored, the length of the pipe, especially with performance headers can
also effect the backpressure on the engine. Too little backpressure can
lead to poor performance, just like too much can. AFAIK, it's not
uncommon to add a longer exhaust pipe to slightly increase backpressure to
compliment a performance header.