[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Back pressure; was Re: got my 2.5" centre pipe!



On Thu, 13 Mar 2003 10:53:20 -0500
"Dan Bubb" <jdbubb@ix.netcom.com> wrote:

> Can you elaborate on this statement about why gas motors need
> backpressure and how this is related to being throttled.

Gas motors need back pressure because the factory fuelling and ignition
maps are set up with the standard air intake and exhaust system. These
are restrictive to make them quiet. Gas motors need tightly controlled
air/fuel ratio or they run like a pig with terrible emissions and fuel
consumption. Also, if you make the mixture richer you need more advance
because it burns slower, so it is all inter-related.

Diesel motors aren't overly worried about the mixture, you throttle a
diesel motor by squirting in more fuel if you want it to go faster or
cutting back on the fuel if you want it to go slower. There is no
throttle butterfly to limit air flow, you just vary the fuel flow. There
is no ignition to worry about, of course. Because of the way diesel
burns the mixture strength doesn't have such an effect on the motor
performance in general.

--Andrew