Carb jets for high altitude?

[vagabond]

Gotta holley 2 barrel on my 2F. It runs great at my home altitude of about 1000 above sea level. I'm worried about a trip to 6-12 thousand feet.
What ideas are there for me to consider?

Change jets when I reach 6000?
And if so, to what size?

jim

 

[Degnol]

Jim, I found this site........http://www.mortec.com/carbtip1.htm

Scrolled down to this.....



Holley carbs are calibrated for sea level operation and an inlet air temperature of 70 degrees Fahrenheit. Once you know the correct stock jetting for your particular Holley carb, you can determine whether you live or race at an altitude above sea level. For every 2000 foot increase in altitude, you can reduce the jet size by one size. If you had a carb which has a stock jet size of 80 and you live or race at 2000 feet above sea level, then you would use a #79 Holley jet in the carb. Similarly, a change in the carb's inlet air temperature may require a change in the jet size from the stock calibration. Many racers go a step further by combining all of the weather varibles, temperature, barometric pressure, dewpoint and humidity with the altitude of the track they are racing at to determine the "density altitude". This is a "corrected" altitude above sea level. From there they can determine whether a jet change is necessary to maintain performance or whether to change their "dial in" (if they are bracket drag racers).



Other than that i don't know diddly about Holleys


GL

Ed

 

[brew8]

If you are spending most all of your time at low altitudes and only occcasionally go to higher altitudes, you can try premium gas it will help with the sluggish preformance at altitude.

 

[donny paradise]

Jim, I found this site........http://www.mortec.com/carbtip1.htm

Scrolled down to this.....



Holley carbs are calibrated for sea level operation and an inlet air temperature of 70 degrees Fahrenheit. Once you know the correct stock jetting for your particular Holley carb, you can determine whether you live or race at an altitude above sea level. For every 2000 foot increase in altitude, you can reduce the jet size by one size. If you had a carb which has a stock jet size of 80 and you live or race at 2000 feet above sea level, then you would use a #79 Holley jet in the carb. Similarly, a change in the carb's inlet air temperature may require a change in the jet size from the stock calibration. Many racers go a step further by combining all of the weather varibles, temperature, barometric pressure, dewpoint and humidity with the altitude of the track they are racing at to determine the "density altitude". This is a "corrected" altitude above sea level. From there they can determine whether a jet change is necessary to maintain performance or whether to change their "dial in" (if they are bracket drag racers).



Other than that i don't know diddly about Holleys


GL

Ed

Hey, ED, that blue print SUX!

 

[Degnol]

Hey, ED, that blue print SUX!

Whadddya mean.........blue?

 

[Degnol]

If you are spending most all of your time at low altitudes and only occcasionally go to higher altitudes, you can try premium gas it will help with the sluggish preformance at altitude.

Larry, that might help with knock, but won't it still run too rich with any grade fuel at altitude? I think Toyota recommends changing jets when running consistently above 6500'


Ed

 

[brew8]

Maybe it's my weber carb, but I live a 3300 feet and regularly go to over 11500 and the premium gas makes quite a difference in power over the pass, maybe I'm just lucky, carbs are the one thing that is a real mystery to me, larry

 

[Biscuit]

I have a Weber with the stock sea level jets in it and live about 750' above sea level. I haven't had a problem with them at altitude.

The reverse on the other hand was a problem...when I first brought my 40 to California (thankfully work paid to ship it ) the jets in for Denver (5280') caused a lot of sputtering as it was running waaaaaaay to lean.

So my vote...jet it for home.

 

[pb4ugo]

When I go to Colorado for a couple of weeks, I just advance the timing. Advance till you get decent idle.