DIY_EFI Digest V5 #28

[Steve]

>
> Date: Tue, 18 Jan 2000 11:57:04 -0800
> From: "Scott Croughwell" <scott at outwest.net>
> Subject: Re: DIY_EFI Digest V5 #27
>
> > How does the hot exhaust gas cool the fresh charge.... Or have I got
this
> > wrong and you mean that the exhaust gas isn't heating the cool intake
> > charge and the cold intake charge is causing the detonation????
>
> Believe it or not... the gasses coming from the EGR have had enough time
to
> cool enough so that the portion of exhaust temp re-entering the intake
port
> is cooler than the intake manifold.  (Thus, EGR valve only opens when the
> engine is at "operating temperature".)  But if engine knock is only
apparent
> at something other than high engine loads and/or speeds... I'd be willing
to
> bet dimes to dollars it's due to the EGR being disconnected or inoperable.

Well, I have put a thermocouple in the intake manifold and can state the
results of what I found.  With the EGR not operating and using a cold air
intake I was seeing around 125F after the throttle body on a turbocharged
and intercooled V6 at light cruise conditions.  With EGR operational, as
soon as the valve opened under the same conditions the intake manifold temp
jumped to 210F on a 75F day.  I think that it is less a temperature issue
than a charge dilution issue.  But with some fine tuning of the spark map,
you can easily eliminate any detonation you may experience.

YMMV

Steve