jesseenglish

HP LOSS = ([elevation in feet] x 0.03 x [HP at sea level]) / 1000

HP loss is NOT dependant on the amount of horsepower you have, it's actually a percentage. The higher you are, the higer the percentage is. It doesn't matter if you have 50 or 5000 horsepower, at 5800 ASL you drop 17.4% of your power because of the lesser oxygen at the higher altitude. You can get this 17.4% figure by substituting the [HP at sea level] as 1.

% HP LOSS = (ALT x 0.03 x 1) / 1000

% HP LOSS = 5800 x 0.03 x 1 = 174/1000 = 0.174 or 17.4% HP loss at 5800 feet ASL.


Given this formula, in Colorado Springs, CO at 6090 feet elevation, my Z has an 18.2% HP loss or 234HP. This sucks!!

350zdanny

That does blow. Does your Z feel sluggish at that elevation? I'm at sea level, so I don't know what that would be like, but I'd hate it!

GrYpS

Wouldn't this formula only apply to NA engines?

Good excuse to get a blower.

bshockley

You should try taking a little Cessna 172 up to 8000 feet. Especially on somewhat hot days...

Juztin

iTrader: (9)

LOL,

I feel your pain as I'm in denver around @ 5400 feet asl. That means that also with drivetrain loss factored in... lets say 16% drive-train loss, the hp @ the wheels would be around 190 HP +/- 10. Hmmmmmmmmmm...... I'd say that my car pulls pretty good, but since we are all runnin sucky a$$ cause of the elevation, I think I should hit a dyno soon!!!

jesseenglish

Yeah, I drove up to Rampart Range Reservoir last weekend around 8700 ft and it felt like I was driving an S2000. It really sucked.


Edit: Oh yeah, and I forgot to figure in drivetrain loss. I can't wait to get my supercharger.

bshockley

I wonder if you could get a variable boost supercharger and hook it up to an altimeter.


You could keep it at a constant 300hp.

jesseenglish

No, but you could do that with a turbocharger setup with a variable boost controller.

GrYpS

Mhm, i don't think hp is affected by altitude in a forced induction engine because the air is compressed into the engine therefore the atmospheric pressure outside shouldn't matter.

jesseenglish

I've never really delved that deeply into wastegates or Bypass valves before, but let me explain how I've always understood it.

A wastegate, be it electronic or manual has to overcome atmospheric pressure, plus whatever PSI the wastegate is rated at.

If it was as you said, someone at higher elevations wouldn't get as much boost, the wastegate would open early because there would be less atmospheric pressure to overcome.

Now unless your wastegate is in a vacuum you should always have to overcome atmospheric pressure. Just like opening a hatch underwater, you've got to overcome the outside water pressure, plus whatever the weight of the hatch is.

So unless I'm totally wrong, which is possible. A person at higher elevations won't have as much power as another with the exact same FI setup at lower elevations.

Any analog boost meter that you see is simply using a barometer type device, comparing outside Air pressure to boost pressure. I do know that for a fact.

350zdanny

Someone was saying that you lose boost pressure at altitude with a supercharger.

I don't think that is the case with turbos, but they have to work harder to push in the thinner air. I think that's how it works, but I'm not sure. SCC had an article on it.

jesseenglish

To get the same kind of HP at higher elevations you've got to figure in pressure drop at your elevation.

To get technical you're engine is seeing more than your 7PSI of boost it's actually seeing absolute pressure which at sea level would be 14.7PSI + amount of boost. So assuming you're running 7 PSI of boost that's 21.7 PSI absolute pressure.

(.47 x elevation)/1000

It's approximately .47 PSI drop for every 1000 ft in elevation. So at 5000ft elevation you've got approximately a 2.35PSI drop.

To get the same amount of power you've got to increase your pulley by 2 PSI for a supercharger.

In a turbocharger you've got to bump up your spring (in a mechanical wastegate), or if you're really high tech adjust your boost up by 2 psi with an adjustable wastegate controller.

So it's actually safer on my engine to run the supercharger at my elevation than at sea level (although I won't get as much power)