[Camaroking98]

Hey guys, been trying to do some research. Haven't really found a definitive answer or calculator...

I just moved to colorado (6700 feet) and I was wondering how I could calculate the power loss.

I've read that N/A loses the most power...then superchargers...and turbos are virtually unaffected.

Just wondering if you guys can help me properly guestimate how much power I'm losing up here.

[CW3SF]

I think superchargers lose the most power. It’s because we make 2-3 pounds of boost less due to the altitude. I’m near SE Aurora. I’ve seen a black 5th Gen ZL1 a couple times in the last few days. Is that you?

[Camaroking98]

Originally Posted by CW3SF

I think superchargers lose the most power. It’s because we make 2-3 pounds of boost less due to the altitude. I’m in SE Aurora near Parker.

Yeah, I understand losing boost. That's what another random forum online said. But I would think that the power loss wouldn't be as bad as N/A because we're still FI right?

[Camaroking98]

Originally Posted by CW3SF

I think superchargers lose the most power. It’s because we make 2-3 pounds of boost less due to the altitude. I’m near SE Aurora. I’ve seen a black 5th Gen ZL1 a couple times in the last few days. Is that you?

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

[Camaro1973]

Originally Posted by Camaroking98

Hey guys, been trying to do some research. Haven't really found a definitive answer or calculator...

I just moved to colorado (6700 feet) and I was wondering how I could calculate the power loss.

I've read that N/A loses the most power...then superchargers...and turbos are virtually unaffected.

Just wondering if you guys can help me properly guestimate how much power I'm losing up here.

Generally for a boosted engine (SC) it’s roughly 1.5% per 1000ft of power loss. N/A loses the most correct, like 3% Turbos also will lose some but It’s more like 1% per 1000ft They may be able to hold boost level but the air is simply not as dense so there will still be some power loss.

Easy fix is to change a pulley to make up for the loss in ambient pressure and your boost will be back, but then you’ll be adding heat by spinning it quicker.

Move back to sea level

[JSH]

The dyno shops and racers here pretty much agree on at least 20% power loss at 8000 DA. In rough numbers, an eleven second sea level car becomes a twelve second car up here.

Originally Posted by Camaroking98

Hey guys, been trying to do some research. Haven't really found a definitive answer or calculator...

I just moved to colorado (6700 feet) and I was wondering how I could calculate the power loss.

I've read that N/A loses the most power...then superchargers...and turbos are virtually unaffected.

Just wondering if you guys can help me properly guestimate how much power I'm losing up here.

[foramus]

Sadly, I believe the power loss is equal to that of NA. Turbo boost is controlled by the wastegate so while peak boost will probably be lower at high altitude, it can usually compensate and bypass less the rest of the time. Supercharger boost is mechanically linked to the crankshaft so it's always making a (maximum) relative boost to the engine RPM. If you're getting 2PSI less atmospheric pressure, then you're getting 2PSI less boost, too.

Not an expert but this is my understanding.

[JSH]

Originally Posted by foramus

If you're getting 2PSI less atmospheric pressure, then you're getting 2PSI less boost, too.

Using an atmospheric pressure of 30Hg at sea level and 24Hg here, you would see 20% less air pressure in your intake manifold when the engine is off here versus Miami

[ZL1Atlanta]

I've never used this particular one, but the Wallace calculators for HP from trap speed are almost right on for every car I've ran through it. It allows for elevation correction on HP.

http://www.wallaceracing.com/braking-hp.php

[arpad_m]

Originally Posted by ZL1Atlanta

I've never used this particular one, but the Wallace calculators for HP from trap speed are almost right on for every car I've ran through it. It allows for elevation correction on HP.

http://www.wallaceracing.com/braking-hp.php

Hmm, at 10k ft elevation a ZL1 practically becomes a sea level SS, interesting.

[Camaroking98]

Originally Posted by Camaro1973

Generally for a boosted engine (SC) it’s roughly 1.5% per 1000ft of power loss. N/A loses the most correct, like 3% Turbos also will lose some but It’s more like 1% per 1000ft They may be able to hold boost level but the air is simply not as dense so there will still be some power loss.

Easy fix is to change a pulley to make up for the loss in ambient pressure and your boost will be back, but then you’ll be adding heat by spinning it quicker.

Move back to sea level

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

Not too bad then. I'm coming from a 392 challenger. Last time I was up here it was an absolute dog...don't get me wrong...it sounded great, but I definitely felt a big loss.

So far the ZL1 still feels much quicker than what the 392 was even in indiana.

[Camaro1973]

Originally Posted by Camaroking98

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

Not too bad then. I'm coming from a 392 challenger. Last time I was up here it was an absolute dog...don't get me wrong...it sounded great, but I definitely felt a big loss.

So far the ZL1 still feels much quicker than what the 392 was even in indiana.

Yes N/A always going to lose the most. How much boost is it making now?


There are many factors but 15-20hp per 1lb of boost is typical.

[Camaroking98]

Originally Posted by Camaro1973

Yes N/A always going to lose the most. How much boost is it making now?


There are many factors but 15-20hp per 1lb of boost is typical.

Honestly I'm assuming whatever it is stock. Got the car just shy of a month ago and been really busy since.

[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.