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Old 11-09-2008, 02:28 PM   #1
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Default Lean burn details

So I'm looking to build a lean burn circuit on my next MS.

I'm looking to enable it under several conditions:
1) highway MPH
2) consistant rpm for X seconds
3) consistant TPS for X seconds
4) EGT below X value

If I read everything correctly, when lean burn is enabled it should lean the A/F ratio and retard the timing to rein in EGTs. This should essentially reduce engine power capabilities, require more throttle reducing pumping losses and increasing MPG.

Is there any basic concepts I'm missing? This project is in the very beginning. Any articles / info / ideas would be appriciated....
--Alex
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Old 11-09-2008, 02:47 PM   #2
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I'm no expert, but here's what I know about tuning for MPG. Run lean and have the timing as advanced as possible to reduce EGTs and improve efficiency. Retarding timing is not the thing to do. And I'll also say this. You **** up and run too lean you'll break your ****. So keep that in mind. I gave up on the idea of trying to run on the raged edge of lean and just run 15:1 in cruise. I still get 32mgp vs the 34 I would get when running 16:1. Not much difference and I feel better cruising at 15:1 without an EGT gauge.
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Old 11-09-2008, 05:24 PM   #3
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I suppose I should have said, run lean and adjust the timing to lower EGTs. This is the article I read a while ago that peaked my interest....

Lean burn - Wikipedia, the free encyclopedia

--Alex
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Old 11-10-2008, 12:19 PM   #4
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You can simply adjust the VE, AFR, and spark tables to accomplish something similar to this, but if you are trying to actively use EGT feedback you would need to modify the code. Right now it just uses EGT for data logging.
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Old 11-11-2008, 01:30 AM   #5
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I think it would be safer to use feedback off EGT. I was thinking of an external processor that took the above inputs into consideration, then when conditions were met, enable the map switching input.

Are there any other negative effect of a lean mixture besides high EGTs?
--Alex
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Old 11-11-2008, 10:29 AM   #6
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seems awfully complicated and unnecessary.
why not just tune cruise a bit lean and allow enrichments to be active when not in steady state, like me and everybody else.
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Old 11-16-2008, 04:07 AM   #7
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Well the same with the same setup I should be able to get rid of the MAF on my OBDII car w/ no CEL. I just happened accross the lean burn stuff and though a few more MPG would be an added bonus for not a whole lot more work at that point.
--Alex
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