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Old 12-15-2010, 04:15 AM   #234
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Joined: Apr 2003
Location: Long Beach, CA
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Originally Posted by GSQuester View Post
Part of my concern about how tweaking things like how rich or lean the bike runs was triggered when I read this post:

From this it seems like the ECU *could* theoretically cause engine damage if it adjusted the AF mixture to run in the "red box" fosters discusses.

I get you, a lot of people think that about AF ratios.

Here's the graph from the link you posted.

See the three vertical dotted lines? The one in the middle is the 14.7 ratio. To the right of that line is a leaner mixture, to the left is richer. Modern catalyst-equipped motors are operated at a 14.7 AF ratio.

Start from the 14.7 dotted line and lean the mixture, looking to the right on the chart. As the AF is leaned past 14.7, the CHT and EGT curves both fall off.

The thing is, the ECU already operates the motor at peak temperatures the majority of the time. So if less fuel is injected, the temperature from combustion is reduced.

Notes. The dotted line on the right is the Best Efficiency AFR, and the dotted line on the left is Best Power AFR.

The bottom curve is Efficiency. It is the inverse of Fuel Consumption.

(The issue from the other post is related to unequal cylinder temperatures, which is an unavoidable reality with the majority of aircraft motors and their fuel delivery systems. The post isn't directly related to the typical vehicle ECU and catalyst-equipped motor.)


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Poolside screwed with this post 12-15-2010 at 02:18 PM
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