Tuning for altitude
 

I'm planning on taking my 382/220 stocker to Bandimere in July. I have typically been running in the 1000 to 3000 foot altitude range, but I expect that going to 5800 feet might require some changes. I will only have two or three qualifying runs so I won't have much time for trial-and-error.

So should I go down one or two jet sizes? Should I add a degree or two of timing? I'd like to start with a good guess before I hit the track for Q1.

Re: Tuning for altitude
 

Dave, put in the loosest converter you can find. I would go down 2 jet
sizes and leave the timing for the second run. Every combo is different
of course, but I have found that the less crank you have, the more effect
it will have in slowing you down. You don't see many people from the
area building too many lower class cars. There are a lot of A,B,C cars &
a lot of stick cars. The locals know how to give themselves a better
mousetrap. Hope this helps.

J.R.

Re: Tuning for altitude
 

If you are going to the Mile Highs in July you can expect to see air 8000 to 10000 ft corrected depending what time of the day you run, last year Weather conditions: air temperature 79 degrees, relative humidity 34 percent, barometer 29.81 inches, adjusted altitude 8,869 feet, track temperature 70 degrees. This track has a cooled starting line, the track temperature on the non-cooled area is 90 degrees and down track it is 94 degrees.
. You will lose .8 in et from the air you are in now. Also you will be pitting a good mile from the starting line, give your self some time for cooldown. Mind you, you can be fast on the mountain with the right combo. Starting line temp can get really hot but with a low hp combo you can add air to your rear tires. Go with lower gear trans [ three speed ?]. Shorter rear tires? If you are the only N car you just have to get under the index. Just drive the car and have fun. Depending on how safe you are with jetting at home down 4 to start with. Your car will feel like its broke, Good luck Tom

Re: Tuning for altitude
 

6.14's ;-)

Re: Tuning for altitude
 

The car will definitely feel like it broke the first pass. Haha. When we ran there a lot and went fast. We changed gear 6.14s to 6.50s put in a looser converter, also ran a shorter tire then we normally did, changed timing a couple degrees, we ran a q-jet but made a multi step adjustment to the rods and when we really wanted to go fast also changed camshafts from what we ran normally. As Tom said if you are the only one in the class and can run under. Change the jetting and call it good and drive it

Rick Ryan

Re: Tuning for altitude
 

Thanks, guys. I'm not prepared to change a lot for this, but these suggestions are helpful. I don't think the budget will allow buying shorter slicks just for this one event, or changing gears. I think the 5.86s will do. But I will try the tuning changes.

I did run at Rocky Mountain Raceway a few years ago and with no changes at all ran under the index, so I should be okay from that point of view.

Re: Tuning for altitude
 

I see from a 30 tall to a 28 tall slick about 150 rpm gain. I have moved cam forward 2 dgrees added timing and 2 steps leaner on carb. All of this using weather station to compare any gai s showed around .15 gain

Re: Tuning for altitude
 

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

Re: Tuning for altitude
 

I run 6 Degrees more timing in Denver than Wild Horse in
the wagon.

Re: Tuning for altitude
 

First pass ever in Denver = I shifted from 1st to 3rd because it was
so long in 1st gear - I thought it was already in 2nd gear.

Re: Tuning for altitude
 

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

Re: Tuning for altitude
 

Do both have carb’s?

Re: Tuning for altitude
 

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. .

Re: Tuning for altitude
 

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

Re: Tuning for altitude
 

Yes they both have the same carbs.

Re: Tuning for altitude
 

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.

Re: Tuning for altitude
 

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

Re: Tuning for altitude
 

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

Re: Tuning for altitude
 

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.

Re: Tuning for altitude
 

thats funny John.