As some of you may know, my Ram has no muffler. Sounds frickin
awesome... probably was the exhaust note and volume that made me buy it
in the first place.... but I've been recently wondering with the high
gas prices, if its hurting my fuel economy.
So not knowing volumes on exhust dynamics and flow, I started
researching. I read that the exhaust flow actually does create a
negative pressure, as in a suction effect... helping to pull exhaust gas
from the cylinder and decreasing the amount of effort the engine has to
used to pump the exhaust out on the exhaust stroke. (thus increasing
power by actually decreasing parasitic power loss through higher efficency)
Have I grasped this concept correctly? If this is the case, I can
clearly see the effect that increasing exhust pipe diameter too large,
or reducing backpressure drastically, can have on this scavenging
effect. It basically takes the suction effect away, forcing the engine
to have to pump the exhaust out vs. having a helping hand pulling it
out... that sound logical? Sort of the same effect you would have with
water in a pipe. A 3 inch water pipe, with the same amount of water
being pumped through it, will flow the water slower than a 2 inch pipe.
Sounds like the trick is to find that sweet spot, where the flow is
not too restricted as to choke the engine, but not too open as to lose
the increased veloscity.
This scavenging effect would also account for why I have heard that
increasing exhaust pipe diameter will help top end (allows the engine to
push more exhaust out at higher RPM when flow is critical to horse
power, at the same time hurting low end, when the engine will see more
benefit from having a suction effect for higher torque. The engine
spins slower at low RPM (obviously) and exhaust flow and pressure is
lower... killing that suction effect.
Again - am I tkinking along the correct lines here? Forgive me if I'm
just coming to knowledge on a commonly known thing. This is one area
(exhaust dynamics) I've never deticated much time or effort to.
Having said this... I'm pondering putting a muffler back on the truck -
perhaps a Flowmaster 40 series, still throaty, but not as raw.
Opinions? Comments?
Tom
-- ------------------------------------------------------------- Rocks are for skipping... I'm all about the mud 75 Honda CL360, 89 Dakota, 89 Dakota 4x4, 95 Dakota 4x4, 96 Neon, 01 Ram 4x4 http://members.aol.com/silvereightynine/ AIM & Yahoo: SilverEightynine
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