How DA affects Compression?
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From: Laguna Niguel, CA
I would think that a higher DA (density altitude) there is more air/oxygen per volume of space and thus, the air is thicker. With thicker air, compression is already done a little bit for you, so you don't need to run as high of a CR to make the same HP at a lower DA.
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Joined: May 2005
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From: 8000DA Land
Thats backwards.. Higher = thinner air...
anyway.. depends on other weather conditions as humidity and pressure.. but higher = thinner air, for sure...
believe me.. i race @ 8000DAs... running a full second slower and more!
anyway.. depends on other weather conditions as humidity and pressure.. but higher = thinner air, for sure...
believe me.. i race @ 8000DAs... running a full second slower and more!
Originally Posted by Luis Castellanos
Thats backwards.. Higher = thinner air...
anyway.. depends on other weather conditions as humidity and pressure.. but higher = thinner air, for sure...
believe me.. i race @ 8000DAs... running a full second slower and more!
anyway.. depends on other weather conditions as humidity and pressure.. but higher = thinner air, for sure...
believe me.. i race @ 8000DAs... running a full second slower and more!
Originally Posted by Luis Castellanos
Thats backwards.. Higher = thinner air...
anyway.. depends on other weather conditions as humidity and pressure.. but higher = thinner air, for sure...
believe me.. i race @ 8000DAs... running a full second slower and more!
anyway.. depends on other weather conditions as humidity and pressure.. but higher = thinner air, for sure...
believe me.. i race @ 8000DAs... running a full second slower and more!
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Joined: Mar 2004
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From: Laguna Niguel, CA
When you raise the compression on a motor that is at say 8000 ft DA, do you have to raise the octane accordingly? Or does the less dense air allow more compression before detonation?
For example a motor at sea level with 10:1 CR needs about 91 octane fuel. If you have a motor at 8,000 DA, could you raise the compression to 11.5:1 and still run 91?
For example a motor at sea level with 10:1 CR needs about 91 octane fuel. If you have a motor at 8,000 DA, could you raise the compression to 11.5:1 and still run 91?
http://wahiduddin.net/calc/calc_da.htm
I like to use www.accuweather.com to get all of the information I need. You can check the last 24 hours of weather by the hour.
I like to use www.accuweather.com to get all of the information I need. You can check the last 24 hours of weather by the hour.
Last edited by ~RedLineLs1~; Jul 8, 2006 at 05:15 PM.
Originally Posted by ~RedLineLs1~
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All else being equal, you need less octane at higher altitude, and that's exactly what the oil companies give you!
Example # 1: I've fueled up in Flagstaff AZ at 7,000 + ft., and by the time I got to Phoenix (altitude ~1,500?) the engine was pinging like crazy...
Example # 2: When I was handling the technical aspects of the Players' Ltd./GM Motorsports Showroom Stock series for Camaros and Firebirds in the late eighties, about 10 cars from Calgary (altitude ~ 3,500 ft.) trashed pistons due to detonation at a race in Vancouver (altitude ~ 300 ft.). It was really hot, and it turned out they had all brought their own fuel from home. None of the local racers had any trouble..
An oil patch dictum is: "Don't ship fuel downhill."
Example # 1: I've fueled up in Flagstaff AZ at 7,000 + ft., and by the time I got to Phoenix (altitude ~1,500?) the engine was pinging like crazy...
Example # 2: When I was handling the technical aspects of the Players' Ltd./GM Motorsports Showroom Stock series for Camaros and Firebirds in the late eighties, about 10 cars from Calgary (altitude ~ 3,500 ft.) trashed pistons due to detonation at a race in Vancouver (altitude ~ 300 ft.). It was really hot, and it turned out they had all brought their own fuel from home. None of the local racers had any trouble..
An oil patch dictum is: "Don't ship fuel downhill."
Originally Posted by 98 Raptor TA
Looks like Texas is 2248 DA
Last edited by ~RedLineLs1~; Jul 8, 2006 at 05:24 PM.
Originally Posted by 98 Raptor TA
Looks like Texas is 2248 DA
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Joined: Jun 2002
Posts: 1,979
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From: Upstate NY
Originally Posted by BlackHawk T/A
I know in airplanes / jets the higher you fly the slower you go because of the thinner air netting you less power, however you use less fuel at the same time.
A jet transport that cruises at 650 mph (true A/S) at altitude would have trouble going that fast near sea level.
A higher DA, or less dense air causes less drag on the airplane or the car for the same True A/S, so you get some gains from high DA, especially at higher speeds on the strip. Pro Stocks aren't that much slower in Denver.
