Can someone explain altitude change to me?

KillaKev702 · Jun 26, 2010

Ok so I went to "The Strip" tonight at LVMS, which is at 2,100 feet above sea level where I ran a best time of 15.0 at 95 mph . I was talking to a guy in the pits and he said that it's the altitude change, thats why I was running slower than used to. Back in VA at Richmond Dragway, which is at 74 feet above sea level I ran a best of 14.2 at 100 mph .
So here is my question, is something wrong with my car or is it altitude? since my old best time I've added 3.90s, FRPP c springs, and an MGW. Also if it is altitude what causes this change?

Deleted member 38176 · Jun 26, 2010

Obviously the more air an engine is able to suck into its chambers, the better it performs. The higher up you go in elevation, the air becomes less and less dense. In other words, the higher up you go, the air gets less and less (as simply as I can put it). With less air, you get less performance.

Have you ever heard about how mountain climbers need to wear oxygen masks? Its because the amount of oxygen decreases the higher up you go. Cars need oxygen too

Stumbaugh · Jun 26, 2010

Nightfire said:
Obviously the more air an engine is able to suck into its chambers, the better it performs. The higher up you go in elevation, the air becomes less and less dense. In other words, the higher up you go, the air gets less and less (as simply as I can put it). With less air, you get less performance.

Have you ever heard about how mountain climbers need to wear oxygen masks? Its because the amount of oxygen decreases the higher up you go. Cars need oxygen too

Very well said my friend. Just like he said, Higher up you go, the less air there is. Car's need air to perform good.

N8Dogg98 · Jun 26, 2010

The atmospheric pressure drop is what causes the air to be less dense. So lets suppose your car made 300 HP at sea level. Average sea level pressure is 14.7 psi, now if you were to take your car to 10,000 feet above sea level the average pressure is approximately 10.1 psi. That means your car would make 300*(10.1/14.7) = 206 HP at 10,000 ft above sea level (assuming temperature and humidity were the same).

It's the same concept with forced induction. That same car at sea level with 10 PSI of boost would make 300*((10+14.7)/14.7) = 504 HP

d98gt · Jun 26, 2010

There are websites available that will calculate your da and "correct" your times.

KillaKev702 · Jun 26, 2010

Nightfire said:
Have you ever heard about how mountain climbers need to wear oxygen masks? Its because the amount of oxygen decreases the higher up you go. Cars need oxygen too

ok that makes sense but do my times make sense? should I be running that much slower from a 2000 ft elevation change? also I didnt mention before that my 60 ft times were pretty much the same as usual if that helps.

Dark04GT · Jun 26, 2010

KillaKev702 said:
ok that makes sense but do my times make sense? should I be running that much slower from a 2000 ft elevation change? also I didnt mention before that my 60 ft times were pretty much the same as usual if that helps.

Your times make sense. I would expect you to run high 14's at that altitude if you had a run just like your 14.2. At 2000 ft your are running at an atmospheric pressure of 13.6 psi versus the sea level 14.7 psi. You lost power over the entire range of RPM's because less air = less boom. Roughly you lost about 13-14 peak hp with that altitude.

KillaKev702 · Jun 26, 2010

d98gt said:
There are websites available that will calculate your da and "correct" your times.

I did check somne of them out and thanks to those I've stopped worrying about something being wrong with my car. According to this calculator ( DA Calculator - Density Altitude Calculator - DragTimes.com ) my car would be running 14.102 @ 102.019 MPH @ sea level.
I'm not liking this higher altitude, now I feel like I'm gonna be dumping a bunch more money in my car to get better ETs oh well...

Barnaby · Jun 26, 2010

I always considered Las Vegas to be low altitude. Last time I ran here the DA was 8800ft.

bhuff30 · Jun 26, 2010

Adjusting for DA is a funny thing. Yes, you lost power, but I would be surprised if you really ran as fast as that website claims you could. It says my 88 is a consistent high 11 second car at sea level, and it really isn't!

That assumes you have perfect traction and could perfectly plant the extra power if you had it. And even at sea level, it i rare for the temperatures to really be at standard conditions, of 59*F and 0% humidity.

ran260gt · Jun 27, 2010

DA is one of the reasons why if you get a new mod you should go to the track a few times to see if you got any HP or faster from that mod !

To many morons get a mod like a T/B or plenum or pulleys or what ever, then run one time at a track, run a slower time then before the new mod, and then go on a forum and bash the said mod for being a waste of money and makes your car slower, thats why when you get a new mod you have to run at the track a few times before posting an opinion !

DA is funny like that, you can run a 13.0 on friday and a 13.4 the next friday !

d98gt · Jun 27, 2010

bhuff30 said:
Adjusting for DA is a funny thing.
And even at sea level, it i rare for the temperatures to really be at standard conditions, of 59*F and 0% humidity.

We get lucky to get negative da here in the winter at HRP That is why running at the track during our summers here is pointless to some; the car can be half a second slower.

3ponyshow · Jun 27, 2010

KillaKev702 said:
I did check somne of them out and thanks to those I've stopped worrying about something being wrong with my car. According to this calculator ( DA Calculator - Density Altitude Calculator - DragTimes.com ) my car would be running 14.102 @ 102.019 MPH @ sea level.
I'm not liking this higher altitude, now I feel like I'm gonna be dumping a bunch more money in my car to get better ETs oh well...

I know what you mean about the frustration. Moving here from NY with it's almost sea level tracks and cooler air made a huge difference in performance. Not only do we have the disadvantage of altitude over most other tracks, but also the extreme heat which has just as much of a negative affect. Don't let it discourage you. Everyone you line up against is in the same position. When you see other's times from other places, just remember you're not comparing apples to apples. Performance mods here are still mods.

KillaKev702 · Jun 27, 2010

3ponyshow said:
I know what you mean about the frustration. Moving here from NY with it's almost sea level tracks and cooler air made a huge difference in performance. Not only do we have the disadvantage of altitude over most other tracks, but also the extreme heat which has just as much of a negative affect. Don't let it discourage you. Everyone you line up against is in the same position. When you see other's times from other places, just remember you're not comparing apples to apples. Performance mods here are still mods.

Oh I know what you mean by the heat, it was about 95 degrees when I ran. I never just never thought that it could be this much of a difference compared to VA. Also your right about the other cars, I was still beating Z28's and s/c cobalts so I'm happy considering I'm pretty much stock except for gears and exhaust.

Can someone explain altitude change to me?

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