Mixture correction for chnage in altitude

I just moved my car from the Midwest at 700 feet above sea level to SW Colorado at 7,000 feet. I have a Demon carb with 83 primaries and 91 secondary jets. I know I will need to lean it out but does anyone have a suggestion about how many steps down would be a good starting place?

Thanks for any help or suggestions.

I'd start at 81 & 89 respectively; Maybe end up at 80 & 88. You might also get away with bumping the initial timing up 3º-4º and advancing the curve a bit quicker.

Thanks for the suggestions. A step down of 2 or 3 is what I was thinking too.

You're also going to lose about 28% of your HP at that elevation. I lived in Denver from '95-'10; the altitude sucks.

yup. hp up there is horrible. you gotta build a car to make power at altitude, but then you can't take it down to sea level without needing race gas

my stock 383 2bbl cuda with just a 4bbl carb swap and everything else stock--and 2.76 gears, was running around 18 seconds in the 1/4 mile on a hot day at Bandimere. (track is around 6,000 feet, DA typically up around 10 from what I've heard, don't know what it was the day I was there, but it was a hot spring day)

I think it picked up 3 seconds when I brought it back home to Ohio!!


but...some of the best scenery in the country is out there in Colorado!

if your motor was running on premium pump before, you might be able to get away with low octane now.