a/f based on length of run

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a/f based on length of run Empty a/f based on length of run

Post  racinghabbit on July 3rd 2019, 1:02 am

I had a motor dyno tuned. Its a touch lean on a 10 second pull.

Now say the racing i do only takes 5 seconds per pass... how does that affect the air fuel? does it get more lean?


Also does cooling your fuel change the air fuel ? lean or rich

thanks.
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Post  rmcomprandy on July 3rd 2019, 9:56 am

racinghabbit wrote:I had a motor dyno tuned. Its a touch lean on a 10 second pull.

Now say the racing i do only takes 5 seconds per pass... how does that affect the air fuel? does it get more lean?


Also does cooling your fuel change the air fuel ? lean or rich

thanks.

Unless the dyno is not capable of supplying enough fuel or the needle & seats have to small of an orifice, the length of the dyno run does not matter for air/fuel ratio.

The specific engine RPM and observed torque output are the relevant factors.

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Post  racinghabbit on July 3rd 2019, 1:32 pm

what about the temp of the fuel?
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Post  Carbguy on July 23rd 2019, 11:31 am

racinghabbit wrote:what about the temp of the fuel?

Fuel Temp is going to have an extremely minimal affect on what you're doing. Cooling the fuel typically will only have an affect if you're running certain additives, or if the fuel octane is marginal for the engine combination.

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Post  racinghabbit on July 26th 2019, 3:55 pm

Carbguy wrote:
racinghabbit wrote:what about the temp of the fuel?

Fuel Temp is going to have an extremely minimal affect on what you're doing.  Cooling the fuel typically will only have an affect if you're running certain additives, or if the fuel octane is marginal for the engine combination.


Thanks
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Post  Dave De on August 22nd 2019, 11:38 am

Randy mentioned needle and seat restriction as a cause. I had this happen to me where I wS using a single dominator with .145" cartridges and E85 with 6 psi fuel pressure. The AFR went lean just after the 1/8th mile about 5.9 seconds into the run and got dangerous from 900 ft on. I went to the largest cartridges I could find from BLP racing .165"
Also stepped up to 7psi
Now its good thru to the stripe at 9.0 with only about 10 degrees coolant temp rise was 30.
This experience cost me a pair of torched P51's and all 4 corner hole pistons. Dont ignore this issue. Delivery to the carb is the most likely cause of this problem. A marginal fuel delivery problem can be worse than a gross delivery problem.
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Post  rmcomprandy on August 22nd 2019, 3:38 pm

Dave De wrote:Randy mentioned needle and seat restriction as a cause. I had this happen to me where I wS using a single dominator with .145" cartridges and E85 with 6 psi fuel pressure. The AFR went lean just after the 1/8th mile about 5.9 seconds into the run and got dangerous from 900 ft on. I went to the largest cartridges I could find from BLP racing .165"
Also stepped up to 7psi
Now its good thru to the stripe at 9.0 with only about 10 degrees coolant temp rise was 30.
This experience cost me a pair of torched P51's and all 4 corner hole pistons. Dont ignore this issue. Delivery to the carb is the most likely cause of this problem. A marginal fuel delivery problem can be worse than a gross delivery problem.

Exactly ... this problem often shows itself when a drag racer has been successfully running 1/8 mile drags and who sees no issue at all ... then he goes to a 1/4 mile track, burns his engine down and just can't figure out what could have happened.
The truth is, it didn't just happen. The issue was there all the time but, never showed itself in the shorter time & distance.

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