[JSH]

Originally Posted by Camaroking98

So by that math, I should be at roughly 590-600 crank still?

I don't see where you told us what it makes. Just take 80% of advertised hp or uncorrected actual sea level wheel hp, and you'll be close enough.

[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)

[Snowwolfe]

When we lived in Colorado Springs I had a supercharger installed on my C6. Shop that did the installation and tuning told me the hp loss is 3% for each 1,000 feet in elevation increase. Guy doing the tuning told me he didn’t think there was much difference between SC, Turbo, or NA. They all lost the same 3% based on what he seen come across the dyno before tuning.
High elevation places are ideal for hybrid and EV’s.

[ZL1Atlanta]

I'd just say don't worry about ET too much there. Race for testing, fun, and winning races against others in the same air. Take a trip if you want to get good ET's.

[Idaho2018GTPremium]

Originally Posted by Camaro1973

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)

I think you are thinking of something else when it comes to "boost". The absolute manifold pressure will be lower because the lower barometric pressure is a lower starting point. That's not the boost pressure I was talking about. I was specifically referring to the pressure increase across the blower; what most people refer to as "boost" and engineers might call gauge pressure downstream of a blower. It inversely is the pressure loss across the system (engine and exhaust). Its lower at high elevations since the mass airflow rate is lower, and thus, there's less restriction.

If you can spin the blower faster to get the mass airflow back to what it would be at a lower elevation, then yes, since the mass airflow is equal, boost would go back up, and the engine would theoretically make the same power (that requires some assumptions, though, e.g., similar blower eff.).

And as far as ambient temperature, I wasn't implying that it is only applicable at high elevations, it is of course applicable anywhere. I was pointing out where supercharging loses more than a naturally aspirated engine (due to the higher charge air temps adversely affecting timing).

[7LitreC5]

Originally Posted by Camaroking98

Nah, I'm near colorado springs. White 6 Gen Z

Is your car a ZL1 1LE? I saw one on Friday when I was out.

[Camaro1973]

Originally Posted by Idaho2018GTPremium

I think you are thinking of something else when it comes to "boost". The absolute manifold pressure will be lower because the lower barometric pressure is a lower starting point. That's not the boost pressure I was talking about. I was specifically referring to the pressure increase across the blower; what most people refer to as "boost" and engineers might call gauge pressure downstream of a blower. It inversely is the pressure loss across the system (engine and exhaust). Its lower at high elevations since the mass airflow rate is lower, and thus, there's less restriction.

If you can spin the blower faster to get the mass airflow back to what it would be at a lower elevation, then yes, since the mass airflow is equal, boost would go back up, and the engine would theoretically make the same power (that requires some assumptions, though, e.g., similar blower eff.).

And as far as ambient temperature, I wasn't implying that it is only applicable at high elevations, it is of course applicable anywhere. I was pointing out where supercharging loses more than a naturally aspirated engine (due to the higher charge air temps adversely affecting timing).

Uhh. I think your confused. The pressure across the blower is lower because the barometric pressure is lower. Bring up the barometric pressure and boost goes up it’s very simple.

Which is why these guys in Denver close to fuel system limits can’t run at sea level because they’ll make many more lbs of boost and be out of fuel.

[JSH]

Originally Posted by Idaho2018GTPremium

the absolute manifold pressure will be lower because the lower barometric pressure is a lower starting point.

Said differently, using an atmospheric pressure of 30Hg at sea level and 24Hg here in Denver, you would see 20% less ambient pressure here in your intake manifold when the engine is off versus Miami, and it would make ~20% less power here.

[Camaro1973]

Originally Posted by JSH

Said differently, using an atmospheric pressure of 30Hg at sea level and 24Hg here in Denver, you would see 20% less ambient pressure here in your intake manifold when the engine is off versus Miami, and it would make ~20% less power here.

In Denver your relative pressure in kpa is about 82kpa. Sea level it’s 101kpa.

So a 19kpa loss, equates to roughly 3lbs of boost.

3lbs of boost isn’t 130hp, unless your elevation is even higher and the kpa is even lower.

[Snowwolfe]

Do any of you have experience dyno testing cars at 6-7000 feet to see what the actual losses are compared to the factory ratings?

[JSH]

Originally Posted by Snowwolfe

Do any of you have experience dyno testing cars at 6-7000 feet to see what the actual losses are compared to the factory ratings?

Yes, tons.

Standard absolute sea-level atmospheric pressure = 14.7 psi.
Denver absolute atmospheric pressure = 11.7 psi.
Difference between sea level and Denver psia = 3 psi
14.7 * .80 (or 80%) = 11.7
Denver has 20% less absolute air pressure than sea level.
LT4 hp @ 14.7 psi = 650 bhp
LT4 hp @ 11.7 psi = 520 bhp
LT4 hp @ 0 psi = 0 bhp
Hp drops 20% for every 3 psi reduction in absolute pressure
Boost pressure, a related but different topic, is the pressure in the induction system in excess of atmospheric pressure.

https://www.engineeringtoolbox.com/a...ure-d_462.html

[7LitreC5]

Originally Posted by Snowwolfe

Do any of you have experience dyno testing cars at 6-7000 feet to see what the actual losses are compared to the factory ratings?

I do, but I've not dynoed anything when it was stock.

Depending upon the DA on dyno day, I've seen 18-20%+ power loss here in Colorado Springs.

[JSH]

Originally Posted by 7LitreC5

I do, but I've not dynoed anything when it was stock.

Depending upon the DA on dyno day, I've seen 18-20%+ power loss here in Colorado Springs.

I've used 20% here today. Madcap in Lakewood told me they use 26%

[synolimit]

go to a shop and run on a dyno using the uncorrected factor. ask someone in say florida using uncorrected also with the same mods or whatever. that'll tell you the difference. however its not just about altitude so it'll be impossible to tell really but you could get close.