[DANACO]

As I understand it, unmodified factory vehicles that are turbocharged and supercharged do not produce the rated horsepower at altitudes above sea level. And again, as I understand it, there are different ways in which manufacturers tune forced induction motors that will vary how close they can or will come to the rated HP at altitudes above sea level.

Does anyone know how the ZL1 HP is affected by altitudes above sea level ?
I live at 5280 ft and often drive to 10,000 ft and above. I’d like to know or be able to calculate the HP loss at these altitudes with our forced induction motor.

[RAT Raceway]

You are down 100 to 150hp from sea level. Just the way it is where we live. Enjoy the car, everyone is handicapped by it so it is what it is...

[7LitreC5]

Depending upon the density altitude on any given day, you can figure around -3% per 1000 foot altitude gain.

Modern turbo engines don't lose quite that much because the ECM will allow for a little bit more boost at altitude.

[gotswap]

I figure we would be lucky to hit 500whp up here.

[JamesNoBrakes]

There are some misconceptions about turbo cars, as in they "keep HP to altitude". This is true for turbocharged airplanes, but not cars. The airplanes try to maintain SL pressure or rated HP to a certain "critical altitude", like 14,000', then they start tapering off. This means the turbo does almost nothing at sea level and is working hardest up at that 14,000 feet. This is not how cars work, cars use the turbocharger to supplement the engine displacement and produce MORE HP at sea level than the engine block would normally be capable of. Because of this, they start tapering off right away, like a NA car. It may not taper at quite the same rate, but often people say that they hold their HP to altitude and they do not.

[DANACO]

Originally Posted by 7LitreC5

Depending upon the density altitude on any given day, you can figure around -3% per 1000 foot altitude gain.

Modern turbo engines don't lose quite that much because the ECM will allow for a little bit more boost at altitude.

This is well known for NA systems but I don’t believe it applies directly to forced induction systems, there is loss but not the same as NA systems loose. It is my guess that turbo chargers are better than supercharges at maintaining more HP due to the parasitic losses of a supercharger and other efficiency factors.

[DANACO]

Originally Posted by JamesNoBrakes

There are some misconceptions about turbo cars, as in they "keep HP to altitude". This is true for turbocharged airplanes, but not cars. The airplanes try to maintain SL pressure or rated HP to a certain "critical altitude", like 14,000', then they start tapering off. This means the turbo does almost nothing at sea level and is working hardest up at that 14,000 feet. This is not how cars work, cars use the turbocharger to supplement the engine displacement and produce MORE HP at sea level than the engine block would normally be capable of. Because of this, they start tapering off right away, like a NA car. It may not taper at quite the same rate, but often people say that they hold their HP to altitude and they do not.

Regarding your last sentence related to vehicles I believe you are correct, what I’d like to know is what is the actual falloff, it may be different for different systems from different manufacturers but probably close enough across them to get an average. I’m pretty confident I’m getting significant benefit form the SC in my ZL1 and the turbo in my Raptor but it’s also obvious they’re not putting out 650 and 450 HP at the altitudes I drive at.

[CW3SF]

I have a turbo diesel Audi Q7 and what I noticed immediately at altitude (Denver area) is that “turbo lag” is horrendous here on a vehicle with larger turbo(s).

That doesn’t seem to be an issue at all with the ZL1 supercharger.

[zincgt]

My car dyno'd 535 uncorrected up here on a mustang dyno and went 11.82 @ 119 bone stock. With that MPH it suggests 545HP.

The physical difference you will see is a drop in boost, less air = less boost. My car makes about 8 psi with stock pulleys, intake and 2" headers

[DANACO]

Originally Posted by zincgt

My car dyno'd 535 uncorrected up here on a mustang dyno and went 11.82 @ 119 bone stock. With that MPH it suggests 545HP.

The physical difference you will see is a drop in boost, less air = less boost. My car makes about 8 psi with stock pulleys, intake and 2" headers

I assume that number is at the wheels, if so, that’s not much drop in HP from what I’ve read on these forums, is that right ?

[zincgt]

Originally Posted by DANACO

I assume that number is at the wheels, if so, that’s not much drop in HP from what I’ve read on these forums, is that right ?

From what I am seeing its not far off from other baselines.

[gotswap]

Originally Posted by zincgt

My car dyno'd 535 uncorrected up here on a mustang dyno and went 11.82 @ 119 bone stock. With that MPH it suggests 545HP.

The physical difference you will see is a drop in boost, less air = less boost. My car makes about 8 psi with stock pulleys, intake and 2" headers

What kind of boost do they make at sea level? Your number really surprises me as I was really expecting that 500WHP would be a gift up here.

[gotswap]

Also, I trapped @ 119.95MPH at PMI

[zincgt]

Originally Posted by gotswap

What kind of boost do they make at sea level? Your number really surprises me as I was really expecting that 500WHP would be a gift up here.

I believe its 11 or so, someone please correct me if I'm wrong.