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Old 10-06-2011, 12:24 PM   #1 (permalink)
Cyborg ECU
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Question Do engine mods change BSFC mapping?

Given the interest in mods of the engine as well as mods of the nut behind the wheel, I wonder...

Is it possible that I have changed the location of the "sweet spot" island on my car's BSFC map by modifying the engine with a WAI, an ignition timing advance by 2*, and removing PS, AC belts, and most alternator electrical load? The car on balance probably has more hp at the wheels now, no? In theory, should that change my BSFC mapping any? I would think it would. What do you think?

If I have changed the BSFC map then I need to readjust the nut behind the wheel... I should expect peak efficiency at load in different parts of the RPM arc than with the stock engine, no? What am I failing to understand that counts?

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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Old 10-06-2011, 12:28 PM   #2 (permalink)
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Yes, engine mods will change BSFC mapping. To what extent we could only guess as we have no convenient way of measuring BSFC.
Current project: A better alternator delete
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Old 10-06-2011, 03:37 PM   #3 (permalink)
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And chances are pretty decent that you haven't moved the sweet spot very far.

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Old 10-06-2011, 04:58 PM   #4 (permalink)
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The changes to the accessories won't change the map at all. The same amount of fuel creates the same amount of power at the flywheel (where BSFC is defined). Because of the reduced accessory loads, however, a greater percentage of the flywheel power will get to the wheels--so to get the same power to the wheel you will be at a slightly lower fueling point on your map but the map itself hasn't changed at all.

Your timing advance will change your BSFC map, because the same amount of fuel will now generate more power. That being said, the shape of the map will probably stay virtually the same--the whole thing will just shift to a slightly lower BSFC.

All that being said, IMO these changes are far too small for you to try to change your driving style.

Diesel Dave

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