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Old 05-22-2020, 10:23 PM   #25 (permalink)
Cyborg ECU
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Join Date: Mar 2011
Location: Coastal Southern California
Posts: 5,807

Black and Green - '98 Honda Civic DX Coupe
Team Honda
90 day: 66.42 mpg (US)

Black and Red - '00 Nashbar Custom built eBike
90 day: 3671.43 mpg (US)
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Originally Posted by Ecky View Post
I'll probably try running 18:1 in a few days. However, there's something to consider with leaner mixtures: ignition timing needs to change quite a bit.

When the mix is leaner, flame spreads more slowly. When timing is adjusted such that peak pressure is where it needs to be, a larger percent of burn will be before TDC or where piston angle is poor. The more I've read about it, the more it surprises me Honda was able to improve economy with ultra-lean burn. Maybe it was the lack of infinitely variable gearing, and lean AFRs were a way to virtually reduce displacement on demand.

In order to get ignition timing right without a dyno, I'll likely need to buy an exhaust gas temperature sensor.
How important are such timing changes under light load? You are at like 20% load at 60 mph, right? Seems slight risk of problems under such conditions, no?
See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.

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