HP at altitude
Thread Starter
Teching In
Joined: Jan 2007
Posts: 33
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From: Salt Lake City, Utah
HP at altitude Guys, I've lusted after some of the horsepower graphs for a while but I live at an altitude of 5000 feet. I looked up what the density is for me and at standard temps and pressures, I am at .83 times sea level density. Does this equal what the horsepower I should expect?
My LS-1 RX-7 dyno'ed at 339 RWHP and 341 ft lbs. In the posts I see by others, they have engines that are more built and when I correct to see what they would put out for me, nothing gets a ton higher and I only have a small cam, good exhaust (no header though), and a tune. I'm thinking that either my engine is something of a ringer or the actual HP loss is somewhat less than the .83 density change I would have anticipated. How does this really work??
My LS-1 RX-7 dyno'ed at 339 RWHP and 341 ft lbs. In the posts I see by others, they have engines that are more built and when I correct to see what they would put out for me, nothing gets a ton higher and I only have a small cam, good exhaust (no header though), and a tune. I'm thinking that either my engine is something of a ringer or the actual HP loss is somewhat less than the .83 density change I would have anticipated. How does this really work??
I'm assuming those dyno numbers were given as corrected, either STD (corrects to sea level) or SAE (corrects to about 600 feet, or approximately Detroit's altitude). To see how much HP your altitude is killing, you'd simply need to look at the uncorrected numbers, which should be in your dyno file (you'll either see the uncorrected numbers or you'll see the correction factor used on that day).
The correction factors make comparing numbers a little easier...it puts everyone on the same playing field so to speak. In reality, your altitude is sapping a good amount of HP, probably on the order of 17-20% given your air density. This would be most noticeable in the quarter mile, as your trap speed would be much slower than if you were at sea level.
The correction factors make comparing numbers a little easier...it puts everyone on the same playing field so to speak. In reality, your altitude is sapping a good amount of HP, probably on the order of 17-20% given your air density. This would be most noticeable in the quarter mile, as your trap speed would be much slower than if you were at sea level.
Thread Starter
Teching In
Joined: Jan 2007
Posts: 33
Likes: 0
From: Salt Lake City, Utah
No, these numbers are uncorrected. In my post, what I have done to see how I compare is to multiply other people's numbers times .83 to see what these engines would do here and from what i've seen, my engine getting 339 hp, at the rear wheels, at 5000ft is really good.
Like I said, my engine has a small cam (222/224) and good exhaust ( manifolds to low restriction cats to 2.5 duals with an X pipe). When I convert the RWHP of others to 5000 ft, my engine comes out way higher than what I'd expect. Maybe I should get a dyno test the next time in CA to see what the real sea level numbers really are.
Like I said, my engine has a small cam (222/224) and good exhaust ( manifolds to low restriction cats to 2.5 duals with an X pipe). When I convert the RWHP of others to 5000 ft, my engine comes out way higher than what I'd expect. Maybe I should get a dyno test the next time in CA to see what the real sea level numbers really are.
Do you just have hard copy graphs, or do you have the electronic files? Typically, the dyno software has the correction factors built in, provided it is hooked up to a weather station of some sort (I guess you could fat finger data in from you local weather service too). Multiplying by .83 is all fine and dandy for the air density, but you have to take the barometric pressure and temperature into account as well for the day you dynoed.
