Tuning for altitude

Dave Muller · 05-31-2022, 06:58 PM

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.

J.R. Haddad · 05-31-2022, 08:17 PM

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.

Tom Meyer · 06-01-2022, 08:44 PM

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

Mark Yacavone · 06-01-2022, 09:14 PM

6.14's ;-)

JRyan · 06-01-2022, 11:42 PM

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

Dave Muller · 06-02-2022, 10:17 AM

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.

Jeff Stout · 06-02-2022, 06:51 PM

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

Chevy55 · 06-02-2022, 07:09 PM

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

GTX JOHN · 06-03-2022, 02:52 AM

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

GTX JOHN · 06-03-2022, 03:05 AM

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.

05-31-2022, 06:58 PM	#1
Dave Muller Member Join Date: Apr 2014 Location: Mesa, AZ Posts: 491 Likes: 159 Liked 221 Times in 71 Posts	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.

05-31-2022, 08:17 PM	#2
J.R. Haddad Senior Member Join Date: Jun 2012 Posts: 628 Likes: 519 Liked 889 Times in 199 Posts	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.

06-01-2022, 08:44 PM	#3
Tom Meyer Senior Member Join Date: Aug 2003 Location: Pierce NE Posts: 901 Likes: 51 Liked 303 Times in 106 Posts	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 __________________ Tom Meyer 5240 SS Stock ??? Last edited by Tom Meyer; 06-01-2022 at 09:31 PM.

06-01-2022, 09:14 PM	#4
Mark Yacavone Veteran Member Join Date: Mar 2002 Location: Miles From Nowhere Posts: 7,420 Likes: 2,587 Liked 4,455 Times in 1,695 Posts	Re: Tuning for altitude 6.14's ;-) __________________ We are lucky we don't get as much Government as we pay for..... Will Rogers

06-01-2022, 11:42 PM	#5
JRyan Senior Member Join Date: Apr 2003 Location: Aberdeen SD Posts: 642 Likes: 28 Liked 104 Times in 28 Posts	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

06-02-2022, 10:17 AM	#6
Dave Muller Member Join Date: Apr 2014 Location: Mesa, AZ Posts: 491 Likes: 159 Liked 221 Times in 71 Posts	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.

06-02-2022, 06:51 PM	#7
Jeff Stout VIP Member Join Date: Dec 2001 Location: phoenix Posts: 1,413 Likes: 53 Liked 657 Times in 257 Posts	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

06-02-2022, 07:09 PM	#8
Chevy55 Member Join Date: Nov 2014 Posts: 305 Likes: 609 Liked 169 Times in 84 Posts	Re: Tuning for altitude Here's an excellent article from David Reher, Reher-Morrison Racing Engines. https://rehermorrison.com/tech-talk-...-with-bad-air/

06-03-2022, 02:52 AM	#9
GTX JOHN VIP Member Join Date: Jun 2009 Location: Boulder City, Nevada 89005 Posts: 2,534 Likes: 2,233 Liked 1,865 Times in 574 Posts	Re: Tuning for altitude I run 6 Degrees more timing in Denver than Wild Horse in the wagon. __________________ John Irving 741 Stock 741 Super Stock Last edited by GTX JOHN; 06-07-2022 at 01:41 AM.

06-03-2022, 03:05 AM	#10
GTX JOHN VIP Member Join Date: Jun 2009 Location: Boulder City, Nevada 89005 Posts: 2,534 Likes: 2,233 Liked 1,865 Times in 574 Posts	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. __________________ John Irving 741 Stock 741 Super Stock Last edited by GTX JOHN; 06-07-2022 at 01:42 AM.