Tuning for altitude

[Darcy Clarke]

One thing I found out a week or so ago is be prepared to turn your fuel pressure down. I ran at Boise with both cars, same fuel and ignition systems and the Stocker Ran good the Superstock was 3 tenths slow. I chased my tail changing everything I could and a good friend I texted said lower the fuel pressure. I did and my 60 foot went from 1.35 to 1.26. Both cars run the same carbs, same fuel pressure but obviously the Superstocker is more sensitive due to the power level. I have passed this along to as many as I can.

6254
A/SA SS/EA
Darcy Clarke

[Ralph A Powell]

Do both have carb’s?

[Eric Bell]

Originally Posted by Chevy55

Here's an excellent article from David Reher, Reher-Morrison Racing Engines.
https://rehermorrison.com/tech-talk-...-with-bad-air/

Years ago I learned, or should I say didn't know I learned, that a properly turned carburetor(s) for the most part takes the same jet at all elevations. The key word is PROPERLY. I would scratch my head thinking this can't be correct. I would change jets on my 6 pack and would end up at the same place all the time. Then, I read the article in the National Dragster from David Reher. A light went off and I thought.....that's what I have found to be true. It just took someone that knows their stuff for me to believe it. Air goes down the venturis and pulls fuel. More air more fuel. At altitude less air pulls less fuel and therefore leans the carburetor naturally. I remember years ago going to Denver with my 6 Pack Challenger. All we did was unload it and race it. I qualified #1 with the same tune-up as sea level. Granted a 6 Pack runs really well in altitude. I'm sure with gear, converter, cam and tire size changes ect. it would have ran better all without touching the jetting. .

[Eric Bell]

Originally Posted by Darcy Clarke

One thing I found out a week or so ago is be prepared to turn your fuel pressure down. I ran at Boise with both cars, same fuel and ignition systems and the Stocker Ran good the Superstock was 3 tenths slow. I chased my tail changing everything I could and a good friend I texted said lower the fuel pressure. I did and my 60 foot went from 1.35 to 1.26. Both cars run the same carbs, same fuel pressure but obviously the Superstocker is more sensitive due to the power level. I have passed this along to as many as I can.

6254
A/SA SS/EA
Darcy Clarke

Darcy.........try that lower fuel pressure at sea level as well.

[Darcy Clarke]

Originally Posted by Ralph A Powell

Do both have carb’s?

Yes they both have the same carbs.

[Ralph A Powell]

When I was working at the Ford Text track in Dearborn we would go on test trips to Denver where Ford had a small facility at Colorado Springs th do high altitude testing on fuel systems and brakes. At that time Ford had High Altitude kits for carb usage over 5000 ft sign included inmost jets,power valves and dist springs. They were in the parts catalog at Ford dealers.

[Tom Meyer]

I think Daves car is a 66 Chevelle 283/220 stocker. The carb on this combo is 485 cfm 4gc maybe with a cast iron 459 intake? Not alot of air flow. Back in the day my SS 283 with the same carb responded to leaning it out with jetting. The 2 plane intake with small lift cam will not have as good as fuel signal in the boosters as my SS motor. Also if he is running a glide with the one gear change, it may respond to higher rpm on the shift. But it is what it is. Good luck. Tom

[The Hawk]

Leave the timing alone, jet up 3 or 4 steps.

[Dave Muller]

Originally Posted by Tom Meyer

I think Daves car is a 66 Chevelle 283/220 stocker. The carb on this combo is 485 cfm 4gc maybe with a cast iron 459 intake? Not alot of air flow. Back in the day my SS 283 with the same carb responded to leaning it out with jetting. The 2 plane intake with small lift cam will not have as good as fuel signal in the boosters as my SS motor. Also if he is running a glide with the one gear change, it may respond to higher rpm on the shift. But it is what it is. Good luck. Tom

That's what it is, except I'm running a metric 200, so there's three gears. I'll give it a little less jetting and a little more timing in Q1 and maybe adjust some more from there. Probably bump the timing up even more for Q2.

[rod]

thats funny John.