I just saw a dyno sheet of a turbocharged C5 making 597rwhp (SAE) @ 8 psi (stock block car). The car made about 520 actual rwhp. I guess the car is at a high altitude. My question is...do you guys at altitude see that kind of correction? I've never seen a dynoject make a 75rwhp or 12% correction.

 

Haha..Since when is Texas High Altitude, 13% is an aweful lot of correction.
I seen the info to..and something isnt quite right for sure.

Dave

 

There's also a problem with the altitude correction for a turbo car. It's due to the fact that the correction is applied to the entire absolute manifold pressure, instead of just the ambient portion.

And the more boost it has, the further off (high) the SAE reasults will be.

 

Couple issues with turbo cars:

First off any non-loading varing dyno like a dynojet cant load the engine correctly. Load dynos like a mustang (eddy current) or water brake setups do a better job. This is because a turbo works of off load, incorrect load on the engine means airflow curves will be way off.

Typical correction factors typical at 4200 ft, 88 deg F, 26 in Hg, 46 % humidity, Vapor pressure = .628 in Hg, Relative Air density = 81.28 (compared to standard conditions)

1. You have altitude correction factors - Here in New Mexico at 4200 feet that would 16% for a Normally aspirated car.
2. Then you have temperature, humidity correction factors - 2.9%

So total correct factor is 19.8 % when corrected from actual conditions to standard conditions. Standard conditions will be slightly higher than SAE conditions. This correction has nothing to do with the turbo or supercharger, the NA cars get this same correction.

The issue people have with the correction is the Realtive density number (81.28) is not correct for a turbo or supercharged car. But guess what it is not correct for a FI car at sea level or at altitude. Only way to correctly calculate for density/pressure changes is crunch the numbers based on IAT, barometric pressure, boost pressure, etc at the engine.

The correction factor is not totally wrong. The air is less dense at sea level with the same boost you will make more power (assuming you have a good tune, fuel, etc,etc,etc)

So the off the shelf corrections factors i.e. "standard or "SAE" are not accurate for any forced induction car. Its unlikely many people will actually perform the calculations for the temperature, boost, and density changes.

So to answer you question have seen 13% corrections and some place like in Denver would probably have 25-30% corrrection factors. Altitude hurts bad.

A stock ls1 at 4200 ft runs 14.2 at 98 mph in the quarter.

Hope that helps

Gary