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Author: Subject: Wast his ignition map done for better mpg
bikecarbfred

posted on 6/7/19 at 07:51 AM Reply With Quote
Wast his ignition map done for better mpg

noob here again.

I remember being on the rolling road n hearing the guys mapping saying the carbs were running rich. they adjusted the fuel mixture then the below map done so it would run leaner between 1k and 2k for better cruise?

i remember the car ran great for air/fuel mixture between this range and then when you opened it up , it would get alot richer.
seems serious advance but there must have been a reason why they did this high advance in these early ranges?

i assume at these rpm's it is hard to get detonation so why not advance very high at these low rpms?



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snapper

posted on 6/7/19 at 09:02 AM Reply With Quote
I am assuming that the left column is for TPS not MAP so small throttle opening/low gas speed = cruise/low load and so the fuel mixture takes longer to burn so you set it on fire earlier for a complete combustion/low emissions.





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bikecarbfred

posted on 6/7/19 at 11:33 AM Reply With Quote
sorry yep. it was tps on left side
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coyoteboy

posted on 7/7/19 at 12:35 PM Reply With Quote
You can get detonation and pre ignition at idle speed. All you need is a hot spot and the right mixture.





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MikeRJ

posted on 7/7/19 at 02:03 PM Reply With Quote
quote:
Originally posted by bikecarbfred
noob here again.

I remember being on the rolling road n hearing the guys mapping saying the carbs were running rich. they adjusted the fuel mixture then the below map done so it would run leaner between 1k and 2k for better cruise?



Ignition maps do not control fuel mixture, or at least not directly. If the carburetor jetting had been set to give a lean cruise condition, then more ignition advance would be needed since lean mixtures burn more slowly.

quote:
Originally posted by bikecarbfred
i remember the car ran great for air/fuel mixture between this range and then when you opened it up , it would get alot richer.
seems serious advance but there must have been a reason why they did this high advance in these early ranges?



There doesn't appear to be any unusually high advance in that map, in fact if it was a two valve engine it's quite low amount of total advance. Look at the bottom line which gives the ignition advance at WOT; the amount required will depend on port and combustion chamber design. Anything above the bottom line is adding advance because the engine is being throttled; incomplete cylinder filling slows down combustion.

quote:
Originally posted by bikecarbfred
i assume at these rpm's it is hard to get detonation so why not advance very high at these low rpms?



Detonation can easily occur in the 3000-4000 RPM range, for many car engines this is close to where peak torque is developed, hence highest cylinder pressures.

[Edited on 7/7/19 by MikeRJ]

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bikecarbfred

posted on 7/7/19 at 02:57 PM Reply With Quote
always also wondered how tuners could hear knock on dyno. the noise in there was so loud.
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