Lean burn engines

[Greg Hermann]

At 9:08 PM 10/17/01, Ray Drouillard wrote:
>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

If you have good control over the advance, having EGR can actually improve
mileage!

Greg
>
>
>----- 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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>
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