At 01:48 PM 12/11/99 EST, you wrote:
>We understand we need a certain amount of back pressure on our engines to
>produce low end torque. Too big an exhaust can loose low end torque. ect.
>Why???? Ted O.
The exhaust diameter must kept small enough so that the power pulses
are kept separated or help pull each other out of the exhaust. The reason
that
top fuel dragsters have 8 pipes is to keep the pulses separate so they
don't run
into each other thereby causing back pressure.
The pulses leave the exhaust port, go through the header or manifold and reach
the exhaust pipe. If the exhaust pipe is too big, the exhaust air expands
to fill
up this volume and, when it does this, it slows down and cools. The hotter
a gas
is the faster it will normally travel. Basically, too large of an exhaust
pipe will
act like a large expansion chamber. The exhaust gasses kind of just hang
around
instead of hurrying to get out. Therefore it doesn't flow as well as a
smaller
diameter pipe would. The bigger pipe has the capacity to flow more than
the smaller
pipe but the engine would have to be able to move that much more air
through the system
to take advantage of it. It would require much larger power pulses to take
advantage
of the larger pipe and not lose its exhaust velocity.
Coutesy of some Ford Ranger guru on the web. Hope it wasn't too
exhausting. (bad pun)
Bob. Southern Ontario, Canada.
'97 Dakota CC Sport, FR, 5.2L, 3.55 SG, auto.
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