Has anyone that has cruised hi altitude , 5k to 10K ft areas, mountiains , etc. made drastic changes to carb jetting? I am thinking about doing the Rockies cruise in Billings, Mt. and am aware of the altitude around the Tetons as well as cruising thru Yellowstone.

I am running sbc with Holley and currently #68 primary and even at my current 3500 ft alt., I run a little rich as I do some runs to 0 elevation on the Texas gulf coast where my pipes will turn gray other than chalky black.

So, has any one made changes to compensate on the fuel? Or maybe this is a case of " bring all your jets issue" ?

Thanks, Don

i live at 5200 feet and race at close to 6000 feet elevation. my carb jetting is almost factory with bumping each jet size down about 2 sizes. i run a holley 750 mech secondaries. jetting is 68/82 w no pv in the rear. car seems to run fine. hasn't it been discussed that what is optimal at sea level should theoretically be optimal at elevation due to the signal and air it has available to pull through?

Im running stock Qjet and on our trip to Seattle thru the rockies on I-94 it never missed a beat, no stalling, no stumbling at all. We also drove to top of Mt McKinzie and down as well, not a problem. Im guessing that if its tuned to run right, it should unless you are wanting full throttle all the time while climbing which takes more fuel and air at the same time. Im not at all sure, but that might be where the problem would come from.
Hope you can make the trip Don. :)

Never spent any time at high elevation, but it might not hurt to have a spare set of spark plugs with you in case you do run into a jetting problem and gas-foul your plugs.

Remember too that when cruising on the freeway you are not usually running on the main jets. You are running mostly on the idle circuit so the IFR and low speed air bleed will affect your A/F ratio more than the main jets (at cruise RPMs).

The high speed air bleed determines what RPM the main circuit comes in at.

A low altitude setup will run better at high altitude than a high altitude setup will run at low altitude. If you're going up in altitude temporarily I wouldn't worry about the jetting unless you're after the peak performance on the car. If you do change jets follow the Holley guidelines ( 1 jet size change per 2K' ) and make sure you change back at the lower elevations.

For our high altitude road racing carbs we have modified the metering plates to work at 6000-8000'. This includes smaller jets, restricted power valve channels and idle channels. We don't change jets, we change the whole metering plate.

Thanks for all input,, basically I operate from 0 on the coast to where I am, 3500. I did a cruise once on my Edlebrock Proflow setup and it did stumble a little at Clines Corner in New Mexico, their elevation was 10K before droping back down but that Trifive is gone . I really don't want to go for all out performance,,, just want to make it up to Billings and back without a tow. Thanks again for all input.
Now if I could pick up a tag a long in Colorado or Denver.

if you let me know when you are going through colorado I could be game to cruise along the non highways (scenic route) up to the wyoming border from denver up.