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Sure, if you're not using flowed jets/nozzles, you can sometimes change from a 90 to a 95 main, and not change a damn thing. It just depends how far off the main jet flows from it's stamped number.
Posts by WJ Birmingham
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Sorry UP... What was I thinking? 
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Better exhaust routing would help.
Think about it this way...
When you're standing on the throttle, you have all of this exhaust pressure blowing the fumes out, and probably away from the vehicle.
When you're idling, that shit is rolling around under the car/truck, finding it's way into the vehicle through every crack it can, fumigating you in the process.
A high speed, or multiple high speeds are used to control the fuel curve, not cure fume issues within a vehicle. Even with one, it will probably still do it.
Think about it this way...
When you're standing on the throttle, you have all of this exhaust pressure blowing the fumes out, and probably away from the vehicle.
When you're idling, that shit is rolling around under the car/truck, finding it's way into the vehicle through every crack it can, fumigating you in the process.
A high speed, or multiple high speeds are used to control the fuel curve, not cure fume issues within a vehicle. Even with one, it will probably still do it.
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Before you even mess with a high speed, which if you're running a high compression motor, can help you lift some ring lands...
You'd be best to know EXACTLY what your fuel pressure is on every pass. I'd hope that when you asked about EGT position, you have a full data logger and not just a EGT logger.
Start your high speed at about 10 PSI less than your top fuel pressure, and start with a VERY SMALL jet. Something in the area of a 40-60. Watch your EGTs and start leaning it down (bigger jet and less spring pressure) until the egt's dont change much from launch through mid track.
Remember, the barrel valve adjustment is your idle mix and to some extent your accelerator pump shot. The main jet on the barrel valve is like the main jet in a carb. The BV adjustment should only be used to control idle temp as well as the response from the whack of the throttle.
After that, the nozzles and main jet (and high speed) control everything once you're at WFO.
If you want consistency out of the system, invest in a weather station and make adjustments every round to the main jet.
You'd be best to know EXACTLY what your fuel pressure is on every pass. I'd hope that when you asked about EGT position, you have a full data logger and not just a EGT logger.
Start your high speed at about 10 PSI less than your top fuel pressure, and start with a VERY SMALL jet. Something in the area of a 40-60. Watch your EGTs and start leaning it down (bigger jet and less spring pressure) until the egt's dont change much from launch through mid track.
Remember, the barrel valve adjustment is your idle mix and to some extent your accelerator pump shot. The main jet on the barrel valve is like the main jet in a carb. The BV adjustment should only be used to control idle temp as well as the response from the whack of the throttle.
After that, the nozzles and main jet (and high speed) control everything once you're at WFO.
If you want consistency out of the system, invest in a weather station and make adjustments every round to the main jet.
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8,263 Posts
Well hell, I guess I wasted all that money on a full flowed jet /nozzle compliment and weather station.
I'll just throw em all up on Ebay dirt cheap.
Sure, if you run it pig fat, it will be consistent.
If you're serious enough about wanting to put a high speed lean out on it, then you should be serious enough to be making fuel adjustments round by round.
I'll just throw em all up on Ebay dirt cheap.
Sure, if you run it pig fat, it will be consistent.
If you're serious enough about wanting to put a high speed lean out on it, then you should be serious enough to be making fuel adjustments round by round.
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