Just dynoed my car and the intake temp was sitting on the 105 degree mark and I dyno at 325. On a older dyno sheet it layed down 300 but intake temp was 71. How much hp difference was losted due to the hot air temperature? I mean, how much would the car have dynoed if it was 70 degrees vs 105. Thanks

 

anyone?

 

Your dyno sheets should indicate "SAE corrected".... that takes temperature, humidity, and barometric pressure into account, so you can directly compare any and all dyno sheets.

As far as what the HP impact would have been without the SAE correction, you loose 6% going from 71degF (=531degR) to 105degF (=565degR). 531 / 565 = 0.940. That assumes the only impact of air temperature is the density of the air entering the cylinders. If there are timing or A/F offsets programmed in, and based on IAT, the impact could be greater.

But, all things considered, the charts should reflect the proper corrections.

 

Let me see if I get what Injuneer said...

so in other words..... a 0.940 loss of power equates to 1/0.94 = 1.0638 wich in turns translates into

your existing hp = 325 times the inverse of your power loss =1.063 comes up to a total of 345.7446"estimated hp.... therefore to answer your question

Estimated HP minus Actual HP = (rounded to two decimals) 20.75HP.


thats without inserting engine power losses due to friction//and other unforseen effects of computer timing, fuel/air ratio... etc


its that near correct?? injuneer?


Marvin

 

Not exactly.

First, IF his sheets are SAE corrected, he has the HP he would see at 60degF and 29.92" baromteric pressure, just like he did when the air temp was 71degF. The SAE correction eliminates the need to further correct for temperature. If a dyno operator gave you uncorrected results, he would not be doing you a favor. The Dynojet correction calculations are a lot more involved and a lot more accurate than the simple method I used.

I simply gave the density change for going from 71degF to 105degF. But SAE uses a different temperature basis... its 58 or 60degF... somehing like that. But you can't play games with the HP if the dyno computer already corrected it. His car probably made about 300HP on the dyno at 105degF, and the correction formula added 25HP to get to 325HP.

 

Ok so the figure Injuneer mentioned (.940) is not correct then...

 

Thanks Injureer and mentalcaseone
The dynos are sae corrected I didn't know that the corrections factored in all of temp info to make all dyno comparable. Learn something every day here.

 

What does degR stand for? and how was that converted from degF?

 

degR = degrees Rankin. This is the english temperature unit based on "absolute zero". Absolute 0 is (minus) -460degrees Fahrenheit. To convert from deg Fahrenheit to deg Rankin, add 460 degrees to degF.

The perfect gas law relates air density to ABSOLUTE pressure and ABSOLUTE temperature.... so to evaluate the effects of temperature change, you need to work in degrees Rankin. Pressure is easier, since barometric pressure is typically stated in ABSOLUTE terms.

 

Old bones... I didnt know that either... so I learned something new too... by the way it would have been nice for the dyno tech to have mentioned the numbers had some sort of correction... I guess if i was the tech I would have mentioned it to my customers as a courtesy. After all, not all of us are well versed in this things ya know...

Marvin