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

[ralexander03@snet.net (Rick Alexander)]

Might I interject that it also has to do with valve overlap. The cams
(diesel vs. gas) have very little in common. A diesel needs no (or very
little) overlap.

Rick Alexander

----- 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
>
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