Lean burn engines

[Ray Drouillard]

Thanks!

One nice feature of Pro-Jection is that I can mess with the spark timing
electronically (once I get my duraspark pickup to fire the HEI module that I
have fastened to my fender well.

I do have open chambers, so I'm out of luck there.  I guess I won't be able
to get it very lean.  Will disabling the EGR help?


Ray


----- Original Message -----
From: "Greg Hermann" <bearbvd at mindspring.com>
To: <diy_efi at diy-efi.org>
Sent: Wednesday, October 17, 2001 8:58 PM
Subject: Re: Lean burn engines


> At 6:47 PM 10/17/01, Ray Drouillard wrote:
> >I have heard that running an engine too lean will cause it to run hot,
and
> >will burn out the valves.  I have never seen an explanation of this.  Why
> >does it happen.
> >
> >Generally speaking, how lean can I run a standard (normally aspirated)
> >engine.  Specifically, (if it makes a difference), I want to improve the
> >mileage of my Jeep Wagoneer, which has an AMC 360 V-8.  It is fed with
> >Holley Pro-Jection, and is fired with a Jacobs Omni-Magnum ignition box.
> >
> >What can be done to an engine to allow it to run leaner.  The engine is
> >currently at the rebuilder (though he hasn't started yet), so I might be
> >able to get stellite valves or something like that.
>
> Stellite faced valves and hard seats in the heads are a good start. A
> thermal coating on the chamber surfaces and the piston crowns will also
> help. You will likely want plugs a bit cooler than stock. A lean mixture
> burns slower, so timing will need a bit of attention in order to optimize
> things, as well. Crane sells adjustable vacuum advance pots---(Your timing
> at WOT should NOT need to change)
>
> As long as you don't rev it way high, setting the squish clearance between
> the piston and the squish/quench portion of the head is a HUGE help.
> .035"--.040" clearance is a good number so long as the revs are kept
> reasonable. This can be obtained by skimming the surface of the block
decks
> (of course, you must also know the thickness of a compressed head gasket
to
> get it right).
>
> If you have seriously "open" chamber heads--with no squish area--you're
out
> of luck on this one.
>
> Best thing to do is tune leaner and leaner until you start getting lean
> mis-fire, then back off perhaps .3 or .4 AFR richer. The more turbulent
the
> chamber is, the further you will be able to go.
>
> Greg
>
> >
> >
> >Ray Drouillard
>
>
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