Today we're going to discuss how the 2025 Corvette ZR1 dyno numbers from Paragon Performance may be unintentionally misleading. We're going to take a dive into their testing, the missing pieces, as well as how horsepower numbers are "corrected".
To be fair to Paragon, I do not believe that they are lying about the dyno numbers, just that there is a more intricate thing to know about the ZR1 performance than was mentioned in their video. I reached out to them to let them know, but it no one wants to be told what I'm about to show you guys hahah.
Lets start by examining the new 2025 Corvette ZR1. It's pretty amazing. A pump gas, emissions compliant 1000+ horsepower car is absolutely no joke. While catalytic converter technology has come an incredible way, normally 1000+ horsepower is going to be run on higher octane fuels like E85. So kudos to GM for making this 1064 horsepower monster (and it's ZR1x variant)!
So with deliveries on the low side as a late 2025 model, of the 40 or less that are currently out in the world, Paragon Performance had the wonderful opportunity to get one on their dyno. And the results sent shockwaves through the industry.
1028 REAR WHEEL HORSEPOWER (STD)
STD? What's that STD you ask? STD is a correction factor that stands for "Standard". The correct factor is meant to make sure that measured horsepower is equal in all different conditions (winter, summer, Denver, the beach). Well, one would assume STD is the standard rating. Nope. It's not the standard in the industry, at least not any more. This one is based off of older correction methods that try to correct horsepower to be as if the car was measured at 60 degrees F, 0% humidity, and at 29.92 inHg. (29.92 inHg is considered the standard atmospheric pressure at sea level and 32*F)
Does a correction factor make your actual horsepower higher? No. It's just a rating to try to make sure your car measures the same horsepower whether you take the measurement in winter (boost weather) vs summer (my car is sooo much slower weather), and different altitudes as air is more dense at sea level. Keep in mind, it's all physics here and more air that gets into the cylinder means you can have more fuel that combine with it, and thus a more power combustion event. So cold air is denser, air at sea level is denser, and 0% humidity means that there is no moisture in the air to take up valuable space for air to be.
So what is the standard in the industry if it is not STD?
SAE - Society of Automotive Engineers
1010 REAR WHEEL HORSEPOWER (SAE)
SAE is the standard by which every manufacturer rates their data. This corrects for higher temperature (77*F) and less dense air (29.23 inHg) and has the same ideal 0% humidity. AND this puppy put down 1010 Rear Wheel Horsepower Rated in SAE.
These are the numbers if you are comparing to engine horsepower that you'd want to use. 1010 Wheel Horsepower vs 1064 Engine Horsepower... is this the most efficient drivetrain ever? Isn't the loss supposed to be like 15%?
Not exactly.
In reality it's a mix of both percentage-based and fixed losses. The only way to know the actual difference is to take the same engine, running the same way, and dyno it on an engine dyno. The results may surprise you. For example, my 2020 Corvette, rated at 495 horsepower, ended up putting 450 rear wheel horsepower down completely stock. This is only a 9% loss. If we say the same percentage since it's very similar drivetrain, with wheel size, brakes, and axles being most of the difference then we would have expected the ZR1 to be somewhere around 967 rear wheel horsepower.
So clearly we think GM under-rated this 1064 horsepower... or do we?
THATS NOT THE WHOLE STORY
This is where it gets interesting. Both SAE and STD are usable correction factors. You'll mostly see STD on a dyno these days because it calculates UNCORRECTED Horsepower numbers to higher numbers, typically about 2-5% higher than SAE. This is why a lot of the internet dyno tooners use STD... it makes customers happier, even if it isn't the industry standard or even the best way to compare on the same car. It's a pet peeve of mine when I see competent shops using that number - but that's a topic for another time.
For round numbers sake, lets say a car dynos in that perfect SAE or STD weather. Uncorrected numbers will match the corrected numbers. But lets say its 100 degrees outside, now the uncorrected numbers, the numbers the car ACTUALLY made on that dyno pull, will be less than the corrected numbers. For round numbers, lets say it dynoed 1000 rwhp (rear wheel horsepower) uncorrected. The correction factor will likely push these numbers to 1025-1040 range.
On the converse, lets say it dynos 1000 rwhp in 40 degree weather. The correction factor will then say it made less, like 920-950 rwhp instead.
Ok - so I just threw a lot of numbers at you and I want you to hold on because I'm about to connect all the dots.
Simply, actual horsepower will go up with cooler denser weather, and down with hotter weather and the correction factor does it's best to keep it solid across the board.
And that's why this is interesting.
The 2025 Corvette ZR1 does not follow such rules.
One of the 2025 Corvette ZR1s most interesting features is that GM claims it raises or lowers the boost so it's always making the same power year round. This isn't like the Stingray which is trying to make as much power as it can year round and you need a correction factor to standardize it. This means, the UNCORRECTED numbers should stay the same year round.
Put on your thinking cap and piece it together with everything I just told you about the way a correction factor works.
Waiting... did you get it yet?
Ok, whether you are ready or not here it is.
If the car puts down 967 ACTUAL rear wheel horsepower like we were predicting in any condition... then in summer the horsepower is going to look insane. And in winter, the numbers are going to look lower than normal. By using the correction factor like SAE and STD, you will actually see swings in the ZR1 power level if you dyno them in different conditions and not use the uncorrected numbers.
If you look at the above dyno graph, it does include the multiplier for both SAE and STD... which means we can back out actual horsepower.
970 IS THE ACTUAL HORSEPOWER
I'm actually laughing in satisfaction right now because this was mostly a theory and as I'm writing this I was able to get the picture above, backed out the multiplier, and the numbers are sooooo close to my prediction that I've got a SEG.
It's roughly the same 9% as the Stringay losses.
And I would expect it to stay roughly the same throughout the year.
Be prepared to see crazier numbers as theirs were done in 82 degrees... and we're rocking higher 90s lately in PA. And once winter rolls around, get ready to see disappointing numbers. But only if you are using a correction factor!
And get ready for customers who get their ZR1 in winter to cry over their numbers.
But you can tell them to read this post. It'll cheer them up!
I hope you enjoyed this informative post. Once we get a ZR1 to the shop for dynoing, you'll get to see these results on our YouTube Channel!