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



Seriously, that is the best damn explanation I've ever heard! And is likely
the basis for the rampant myth surrounding the need for backpressure.
So, if you have CIS injection, that is damn good at maintaining the A/F
ratio for varying airflow, then no lose of torque with low backpressure!
Dan

----- Original Message -----
From: Andrew Basterfield <list@cemetery.homeunix.org>
To: Dan Bubb <jdbubb@ix.netcom.com>
Cc: <drew@scirocco.cs.uoguelph.ca>; <skerocdriver@juno.com>;
<scirocco-l@scirocco.org>
Sent: Thursday, March 13, 2003 11:04 AM
Subject: Re: 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