OK...perhaps a compromise then. I decided to do it this way. I posted the derivation of the SAE J1349 correction factor here:
http://www.modularfords.com/forums/2...ion-54094.html

Introduction
Most everyone is familiar with the usual SAE (or STD) dyno correction factor, which are used to scale the measured power and torque to what would be measured at some reference set of ambient (weather) conditions. (For SAE J1349, these are: absolute ambient air pressure of Pref = 990 mb, ambient temp of Tf = 77 °F, and RH = 0%.) These correction factors were developed for naturally-aspired engines wherein the intake manifold pressure goes in direct proportion to the ambient pressure. (See link to the derivation given above.) Therefore, the scaling factor (αp) for indicated power with pressure has the inverse relationship and goes simply as

αp = Pref/Pdry

where Pdry is the dry-air partial pressure at the time of the measurement and Pref is the reference air pressure. Since it can be shown that the boost pressure (and hence the total intake manifold pressure) for an engine with a P-D supercharger is also directly proportional to ambient pressure, these correction factors still apply for these cases as well, at least to first order. (It will not correct for changes in the parasitic drive power of the SC as air density goes up and down, for example.)

For a turbocharged engine, however, this is not the case. Since these setups typically employ boost controllers that are designed to keep boost pressure constant, the total intake manifold pressure is less affected by changes in ambient pressure. (It is still affected since the intake manifold pressure is the sum of ambient plus boost pressure, but to a lesser amount.) As a result, turbocharged engines don’t gain or lose much power as the atmospheric pressure changes up or down. Therefore, the standard SAE J1349 type correction factors are wholly inappropriate for turbocharged applications. Below is a description of how pressure would scale for a typical turbocharged engine with boost controls to keep boost constant.

Turbo correction factor
Skipping all the math, (if someone really wants to see it let me know), for a turbocharged engine with a constant boost pressure, (after the turbos are fully spooled), it can be shown that the indicated power and torque would scale with pressure as

αp = (Pref + Pb)/[Pdry(1 + Pb/Patm)]

where Pref is the reference dry-air absolute pressure (29.235 in-Hg for SAE), Pb is the boost pressure also in in-Hg (= 2.036*PSI), Pdry is the absolute dry-air partial pressure at the time of the measurement, and Patm is the total absolute air pressure at the time of the measurement. To get the brake power scaling, clearly the mechanical efficiency needs to be factored in here as well. (See that other thread).

Below is a table showing how the two correction factors might differ for a turbocharged engine measured at a mile high with everything else at SAE J1349 conditions; Pref = 29.235 in-Hg, RH=0%, etc. There are other assumptions that I'll not get into here. Note how the “typical� correction factor overestimates the results and gets increasingly worse at higher boost pressures. It should also be pointed out that the difference between the two will change as the other conditions change. For example, as the absolute ambient pressure approaches the reference pressure, the difference is reduced.

For the above conditions, the SAE J1349 correction factor is: CFsae = 1.254

First column = boost pressure in psi
Second column = boost pressin in in-Hg
Third column = dyno CF appropriate for a turbocharged engine (CFturbo)
The 4th column shows how much the SAE J1349 CF overcorrects the results (relatively speaking), i.e., 100%(CFsae/CFturbo - 1)

.......the percentage of power loss between a naturally aspirated engine and a mechanically supercharged engine is close enough to be considered the same. This is what SAE corrections on dyno’s is designed to compensate for. They are basing the results at a certain altitude (and temperature but it won’t be discussed here) and try to get their results back to sea level on a perfect day. This is a set standard and makes numbers from other dyno’s easy to compare. This correction value is based on a set % for altitude and temperature. This is fine for naturally aspirated of mechanically supercharged vehicles but is worthless for exhaust driven turbocharged vehicles. This is because mechanically driven superchargers are boosting to a certain set ratio of air greater than what the engine is actually sucking in. An exhaust driven turbocharged vehicle is set to reference pressure to sea level. At higher altitudes it just works harder to get that pressure back up. It has to work harder since there is less pressure to start with........The total gain is different and calibrated to a fixed, known location. This is why you use SAE corrections for naturally aspirated and mechanically supercharged engines but not for exhaust driven turbocharged engines. SAE correction factors for turbocharged vehicles will basically be the same as giving you some free boost. That's cheating the numbers. It may be great way to sell more product but it isn't an accurate representation of how much power you put down. The greater the altitude change, the more inaccurate it becomes.

In reality, there are some differences that offset the effect of turbochargers holding boost at higher altitudes. First off, the turbo is working harder since it has to spin faster. This creates more heat. we also have an average loss in temperature of 3 degrees F over every thousand feet in elevation rise. While these will affect the final numbers from sea level a small amount, they are nowhere near as off as the SAE correction factor for turbocharged engines at altitude. The other thing to consider is that your turbo may get well out of it's efficiency range at these speeds. Different turbos will have different results so you can not have a set standard.

The next time someone tells you that you need to use SAE correction for a turbocharged engine because it is the "standard", laugh at them, tell them to go do their homework and to just go ahead and print up your uncorrected dyno sheet (turbo cars) so you can leave.