[Camaro1973]

Originally Posted by Idaho2018GTPremium

It's a complicated engineering question. Supercharged engines lose power at elevation, just as all engines do, if they aren't compensated to make up the additional mass airflow rates required to make the factory hp rating.

Under some conditions (e.g., cool air), it's correct that the supercharged engine loses less percentage of its power at elevation than a naturally aspirated engine because the supercharger is able to force air through the engine.

However, a supercharged engine loses more percentage as temperatures climb than a naturally aspirated engine due to the heat of pressurization. At higher temperatures a supercharged engine has to pull more timing causing a larger loss of power since the charge air is much warmer than a naturally aspirated engine in the same conditions.

A balance between the two is required to estimate your hp as elevations and temperatures climb or drop.

People see less "boost" at high elevations because the mass airflow rate is lower, thus, less pressure drop, which is really what the boost pressure is conveying - the pressure drop through the engine and exhaust system. Lower mass airflow rate = less hp. To get that power back you have to get the mass airflow rate up.

So actual hp varies dramatically depending on air temp., conditions, and elevation.

Note that the SAE engine rating conditions correspond to a density altitude of about 1800-2000'. So, if the DA in your area is ever 2000' (e.g. on an extremely cold day), the engine will be making around 650 hp.

Sorry there's not one simple answer. I'd suggest that if it's cool out you use 1.5% loss per 1,000 ft of elevation, but if its hot, use 3% per 1000 ft. If it's warm, use something in the middle.

Use airdensityonline.com and find a local track to get your DA, then you can start making comparisons based on the percent loss values noted above.

You could theoretically over spin the blower to force more mass airflow rate through the engine with a pulley upgrade. It would create more heat since it would be operating at a less efficient blower speed and it would be making more boost than the stock pulley. However, the OEM intercoolers could likely handle it because it is likely still creating less boost than originally designed for due to the elevation, and would likely fall within the designed limits at such high elevations.

Other power mods will also help, obviously, like ported TB, ported S/C, etc.

I've simplified the response quite a bit, but that's the intro to it.

You lose boost because barometric pressure is lower at higher altitudes. The rest about cold days, hot days is just another factor. Regardless of altitude on hot days your simply going to lose more power because of the heat.

DA factors all of that in, elevation and atmospheric conditions. Temperature, humidity and elevation are all calculated.

If you take the same car, same temps but different elevation say 6000ft to 1000ft and at 6000ft it makes 75hp less because it’s lost 3lbs of boost, if you increase the boost back to where it was at 1000ft theoretically it should make the same power. (Keyword here is same temps)