Carb jetting 1

[mdwagonman]

After drag racing several different cars for over 25 years I am still stumped with carb jetting. I have tried the new weather station computers and they just don't seem to work for my car. Coming up with an adjusted altitude based on temperature, humidity, and barometer and using it to pridict performance just doesn't work. Seems like barometer has the most effect on performance. I am running a 12 to 1 compression 383 chevy smallblock that runs 10.70 to 10.90. When the weather station says the air is worse(higher altitude reading) I would think my exhaust temp would go down, but it goes up. Any ideas?

 

[Lou Scannon]

These days, anyone serious about tuning uses a wide band AFR analyzer. Running in the 10s tells me you're pretty serious.
I'd recommend you first dial in the AFR, then fine tune with spark timing. Spark timing can and should be advanced to compensate for lower barometric pressure or higher humidity, at a constant AFR.

 

[mdwagonman]

So you think the fuel burns slower when the barometer is bad and that means the fuel is still burning as it goes out the exhaust causing higher exhaust temp? I guess that would make sense. Racing season is over here so I'll have to wait until spring to figure it out.

 

[patprimmer]

Lower barometer means lower effective cylinder pressure due to compression, so you can light it a little earlier and still not build cylinder pressures to the point of detonation.

Regards

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