C7 Corvette ZR1 Owner at High Altitude Seeks More Factory Power

Corvette ZR1 owner wants to add a pulley to get back to 755 horsepower, but he may need to add more.

When the 2019 Chevrolet Corvette ZR1 or any other new model sold in the United States receive their official engine output ratings, the engine is run in a dyno room in controlled conditions. Those conditions are generally set to an average in terms of temperature and air quality, so an engine like the LT5 in the new ZR1 will make more power at sea level and less power at extremely high elevation.

In other words, the C7 Corvette ZR1 makes less power in Denver than it does in Detroit or Miami, leading “robmypro” to ask the community what upgrades are needed to lift the LT5 to 755 horsepower at a mile above sea level.

Corvette ZR1 Altitude Adjustments

When the OP posted his question in the C7 ZR1 Discussion section, he got right to the point.

“Hey guys since I live in Colorado I figure I am losing 15% horsepower. If I wanted to get it back what size pulley would I need, and where would I buy one from?”

We don’t know for sure that the 15% estimate of horsepower lost due to the extreme elevation is accurate, but if it is, the LT5 in the OP’s super-Vette is only making around 645 horsepower. Even if the estimate is too liberal, the new ZR1 is likely making around 100 less horsepower in Colorado than it does in ideal conditions.

With that in mind, he wants to add a smaller pulley to pick up the lost power, but he might be too ambitious with his expectations from just a pulley swap.

The Community Responds

The first person to respond was “6Speeder”, who lives at roughly 6,000 feet in New Mexico and who went through a similar process to get back some of the factory power in his Z06.

I’m at 6,000 ft. and, like you wanted to get back to stock power levels at this altitude. My car is a Z06 so not exactly the same as your situation, but close. I don’t think you’ll get there with just a pulley. I believe a 15% overdrive pulley will spin the blower too fast, generating too much heat (others may disagree). I went with a ATI 9% overdrive, a Halltech CAI, and NORCAL downpipes. These mods took me from 8.5 PSI boost (here at altitude) to 11 PSI. Ran great but not where I wanted. I then added a flex fuel sensor and run E-65 – E-70, That’s what we get from the E-85 pumps here. With a tune to use the fuel’s capability’s I’m where I wanted.

Be careful, the stock fuel system will be tasked to the max. Check your AFR’s, fuel pressure, and injector pulse width in milliseconds, DI motors are not like port injected motors, they can’t safely take long injector pulse widths. You MIGHT have to run less E-85, maybe a mix of premium and E-85, getting down to E-40 total.

Based on that information, the OP had more questions.

Great info. Thank you! So would the ATI 9% overdrive pulley get back 9% of the power loss, or increase the lower powered engine by 9%? So let’s say at 6000 feet i am losing 18%, which means 755 hp is really 620. If i ran a 9% pulley that gets me 620*1.09 = 675. Is this correct? Add the GM air intake and that gets me another 15 hp. Throw in a Corsa x-pipe and maybe i am around 710. Not bad, but still around 45-50 hp short.

That was met with some bad news for the OP from 6Speeder.

I wish! The 9% means it spins the supercharger 9% faster, not 9% more power, on the Z06 it gained me about 30 RWHP. The Halltech or the AFE will outperform the GM intake (if the GM is even still available). On the Z06 the Halltech added 40 to 50 RWHP, the AFE about the same. At altitude I got away with these two mods ON THE STOCK TUNE, YRMV. The other mods I listed will void your warranty, so choose wisely.

Which Cold Air Intake?

Finally, while 6Speeder recommended the Halltech cold air intake, the OP found that the company doesn’t offer one for the ZR1. There seems to be some doubt as to whether or not the coupler for the Halltach intake will fit the larger throttle body of the ZR1, but more importantly, the Halltech air box won’t fit in the ZR1 engine bay.

Fortunately, “C7Z06 Man” posted a picture of the LT4 in his Z06 with the larger ZR1 throttle body. He has the AFE cold air intake and the coupler was big enough to stretch over the huge throttle body inlet, including a picture of the fitment.

If you have experience with picking up power at high altitude or if you have input in general on how to pile on 15% more power in the C7 Corvette ZR1, click here to head into the original discussion.

.