Azurro_California_911

Does anyone know, of is there a formulation, to calculate the loss of power due to higher altitude in naturally aspirated engines. I notice a big difference when I am driving at sea level, as opposed to driving in Reno, NV, altitude 4500 feet.

JFS

MJones

Google is so cool > search > altitude hp loss
http://www.wallaceracing.com/braking-hp.php
Plus a bunch more

Azurro_California_911

Wow according to Wallace Racing there is roughly a 13% loss in power, interesting. Thanks

Vintage

That high altitude horsepower loss really sucks, doesn't it Azurro. I live at the same elevation you do and there definitely is a difference from sea level. I believe, though, that turbocharged engines overcome some of that loss because more oxygen is being crammed into the cylinders. MJones, are you listening? Do you know if that is true and if so, how effective are turbos at overcoming the effect of high altitude? According to your calculator above, we lose 47 HP at 4500 feet. That is a lot!!

Azurro_California_911

You are correct Vintage, the turbo compensates with the forced induction. I don't know what the power loss is at altitude, but from my experience the turbo feel as strong at different elevations.

mbodo

Depending on the output of the turbo and what pressure the wastegate is set at, your turbo could continue to provide "maximum boost" at very high altitudes. Case in point, a lot of light aircraft single/multi engine piston aircraft don't see a power loss until over 15-18,000 feet, albeit these turbos are really only putting out enough pressure to compensate for the lack of atmosphere at altitude. I think anything above 12,000 or there abouts requires bottled oxygen for operators.

Paul523

Does a supercharged engine suffer the same proportional power loss at altitude due to oxygen deprivation as a normally aspirated engine since the SC is chain/belt driven from the crank, or does SC compensate like a turbo?
Getting dumb and dumber as I get older..

I'm thinking of buying a Shelby GT500 to keep at our place in Colorado.

Edgy01

According to that I need a GT3 to keep Carrera S power levels in Denver!

rdstemler

You have to do what you have to do!!!

What color are you getting???

meaker

Top fuel Drag cars with tthere blowers still lose a little power at higher altitudes tracks. I think with a street car that is supercharger the lost would very little, if any.

NNH

Boost is measured relative to local atmospheric pressure. So if your turbo wastegate is set to 5 pounds, then the at sea level engine sees 15psi of atmospheric PLUS 5psi of boost - all things being equal, that would turn a 300hp naturally aspirated engine into a 400hp engine. (I'm ignoring a lot of additional engineering factors here, but bear with me).

At altitude, local atmospheric pressure drops. For instance, at 6000 feet, atmospheric pressure is about 80% of sea level, or ~12 psi (see eXtreme calculator) , so the same turbo wastegate will add 5psi to give you 17psi at the engine intake - a 3psi loss or 15%, dropping our aforementioned turbo engine's output to 340hp. Still, you've got to feel for the non-turbo driver, who has seen a 20% drop in intake manifold pressure from 15psi to 12psi, and a 20% drop in power to 240hp.

So there you have it - turbo engines with conventional wastegates do suffer a little at altitude, but not as much as naturally aspirated cars. I suspect that true aviation engines have a different wastegate system that is designed to achieve a specified absolute pressure, instead of boost relative to local pressure.

tkids

Your lucky down there in Reno, up here in Truckee........................

Your BHP loss computed from your BHP of 355 at sea level and Elevation of 6200 feet is 66.03 HP loss

Edgy01

Perhaps that's why I never noticed the power drop in my turbo when doing mountain roads. It is very little. I thought that Porsche has an barometer in the design of the car so that it can adjust the mix and keep as much HP despite the thinning air.

Paul523

Thanks for the explanation NNH, Meaker.