SPOautos

damn, forum crashed and lost my post

Mr rx-7 tt

iTrader: (5)

Before I push "send" I always highlight and save my post, if the forum crashes I just repaste ad send it again.

nocab72

I would say nope! Never saw anywhere in the dynojet software a click box for "boosted" or "n/a". It's a generic correction factor and likely inaccurate for turbo cars. But I'll run this question past my dyno guy for confirmation.

K

infinitebass

But as long as you are comparing FI to FI, it should scale correctly and be accurate. Of course, comparing NA to FI, that might be skewed towards one or the other.

Is that correct?

Blake

SPOautos

Not really cause the problem is this...

This is totally generic numbers just to make an example.

Lets say there is a guy in the mountains that dynos 300rwhp and the dyno corrects it so that we would know what that car would make a sea level and lets just say uses a 20% factor which is based on a formula for a N/A application. With this formula its going to tell him that at sea level on a perfect day his numbers would be 360rwhp corrected. The prob with that is if the 20% is based on data for N/A applications and isnt a correct assumption for a FI car it would scew the numbers. What this means is since the correction factor is wrong if the car actually went to sea level on that perfect day and tried again it wouldnt come up with the 360rwhp that the corrections estimated because it was based on a incorrect factor.

Personally on my car when I go to the dyno I use STD cause that is what my car is making right then in its own environment. I'm not worried about what it would do somewhere else.

I found a really good link about this one time, I'll try and dig it up.

just my .02
STEPHEN

RICE RACING

Now unless I am missing something, all we are correcting is atmospheric conditions, not boost pressures ?

The "quality" of air injested through the compressor is what is corrected for nothing else. What the turbo does with it is another story all together or am I missing something here ?

It is early in the morning (here)

Marshall

Stephen, STD horsepower is corrected -even moreso than SAE. If you want to know your actual horsepower, then don't correct to STD or SAE, just get actual.

RICE RACING

I know there are other issues such as the thinner air reducing the effectivness of the charge cooler so that is another factor not taken into account I suppose ?

Marshall

Correct Peter, all a correction factor in this case really is is a density altitude ratio. Take the actual DA when you dyno, divide it by the DA of another atmosphere (whether it be an STD or SAE atmosphere) and multiply that by the hp you made.

SPOautos

Yea, your right....I go by actual I was just in a hurry and typed the wrong thing. I usually do both just cause people always want to see it "corrected" but for my personal use I go by the actual

sorry about that

STEPHEN

fatboy7

The reason that the standard isn't so standardized has to do with compressor and intercooler efficiencies, and pressure ratio compensation.

For instance, I live at a relatively high altitude (4400 ft). If you were to compare the atmospheric air pressure here, it will vary between 2.2-3.0 psi less than at sea level, and aproximately 12-18% less dense, depending on the temperature. For NA engines this is very easy to just plug in the changes in the oxygen partial pressures between different dynos, and conform them to a standard pressure, humidity and temperature.

Forced induction is a means to change the charge desity from that which is naturally provided. For me, pressure ratios are higher here than at sea level. Effective atmoshpereic pressure here is around 12psi. So for me running 15psi puts my turbo in the same pressure ratio as you running 18.4psi, only with less lbs/min flow. OK, so compressor output temps on mine will be higher, proably around 10*-15*F hotter. Now look at absolute pressure differences running the same boost. I'm running 27psi absolute, while your running around 30psi absolute. Before I was had 18% less pressure than you, now I have only 10% less, but at a hotter temp, so my probably would show 3-5% more SAE than the same car at sea level.

Then intercooling comes in. The cooler the outside temps are, the more the intercooler becomes an added benifit to a turbo'd car. Lets say that the turbo compressor is 70% efficient, and the pressure going and 14.7 psi boost. Say my intercooler is 65% efficient. Now compare the difference in density compared to the standard. Lets compare at 30*F and 100*F. Ideal gas law in physics says the the diffence in density for the 30*F air is 14.2% more dense than the 100*F air. Compressor outlet temps would be 186*F and 256* respectively. After the intercooler the temps are 85* and 155*. Now the difference in density is 12.9% so the turbo engine would dyno at 1.4% less SAE power at 100*F. If you could obtain the 100% efficent IC, then you'd make the same corrected HP regardless of temp. But to make matters worse, dyno's typically don't bring out the best in your IC. With no IC, the difference is 3.5% less. Add more boost, or run the compressor at less efficency and 2-3% percent less is quite common on a dyno. Humidity also as a similar effect as IC efficiency, because water vapor is harder to intercool.