I went to the drag strip Friday night for the test and tune (spectator)for the first time in over 30 years :eek: Yes its been a while. After reading a lot of times posted on here by some of you fellas it got me thinking about how much does the elevation affect performance. We are at about 3740' here. A lot of cars were in the 14's, a big block chevelle and Beaumont were in the low 13's and a few others made it into the 12's.I was going to ask a few of them in the pits about their motors but decided not to bother them as they all seemed pretty busy getting ready for each run.I am going to have to watch for Ryan(66 283) when he gets his going again and make sure I get out to watch. A couple of things that were pretty obvious is that the cars ran better when the sun went down and it cooled a bit and that they must not do anything to the track at test and tunes because some were breaking the rear tires loose a couple hundred feet down the track.
I am planning on building a 383 for mine this winter, not specifically to race but may try, and it seems I am going to have to build something pretty strong to get to the low 13's at this level. I know I only seen a few cars from this area race Friday but it kinda left me with the feeling it going to take awful big power here to get to that goal.

Altitude plays a huge part in how much power an engine makes. The higher it is the slower the car. Here is the NHRA's Altitude Correction Chart (http://www.nhra.com/tech_specs/altitude.html). As it cools down at night the Density Altitude (which is the altitude the air is at - correcting for humitity, temp, and air pressure) drops and the engines make more power. Unless you are stuffing air into the motor with a blower, all engine are subject to this (it's a really serious issue with some airplanes, climb rate can drop dangeriously).

The top chart is very accurate for my ET's. I've raced at 5800, 5200, 3000 and 1300ft actual elevation tracks. Using the chart to compare, it comes very close. It usually isn't as much as you hear people say.

When I was out in Cal. I used to run at LACR which if I remeber correctly was at approx. 2,800' and the air was generally anywhere from 3,400' on a good day to up over 5,000'. My car ran 12.80's @ 110 consistantly. I took it up to Famosa in Bakersfield and only got to make one pass. Without any changes at all it ran 12.11 @ 112 and I had shut it down at approx 1,000' due to lost fuel pressure.

Density Altitude is pressure altitude corrected for non standard temperature. This means that as temperature increases the altitude that the engine "sees" will increase. for example if you are at say 1300ft above sea level (PA) and it is 100 degrees out the air will have an equavalent density to air at 5000ft (DA) (not exact numbers just an example) the air being less dense will relate to the intake charge being less dense and thus less performance. It is also the reason sometimes you will hear corrections on a cars ET based on altitude. (or a sea level correction) I am a pilot and this is a very big problem because of reduced climb performance (airplanes) and reduced rotor effieiency (helicopters)

blumont,

The elevation is about 3150' at the track but the density altitude is typically between 5000 and 7000 feet. On friday night it was about 5500 I recall.

Not much air here!

If you are in the planning stages don't bother calculating a dynamic compression ratio :rolleyes: . You can get away with a lot more compression on the same fuel here.

I have a friend who has ran about 12:1 in his SBC on pump gas (92) with a moderate camshaft and no detonation.

You've got my number - give me a call and I'll get you in touch with him.

Your best bet to run hard with the thin air is to run a blower or nitrous. I'll get you hooked on nitrous and then you'll be coming to my garage every weekend to refill your bottles. LOL

graemlins/beers.gif

Oh, and on friday nights they do not prep the track WHATSOEVER that why I almost hit the wall every time out. I made no changes between a friday night and a saturday test and tune (prepped) and my car went almost 3 tenths quicker in 60 feet and a half a second faster ET.

DA plays more of a part than you think on a blower motor. Not so much because the pressure is lower but because of the humidity. Humidity is part of the DA calculation and high humidity will affect a blower motor because the moisture in the air displaces the oxygen. We can run the same boost pressures on consecutive runs but we tune to DA because we have less oxygen to burn with the fuel. It may not be as evident on lower powered engines (comparatively) but we are making 2400 HP on the altered and a change of 1000' will make a couple tenths difference mostly because of the humidity here in Florida. JM2c.

Troy.