Hello all
I used a Gtech Pro RR performance meter to determine the affects of ambient air temperature on horsepower (bone stock 2006 Cobalt SS Supercharged). The Gtech Pro RR meter uses accelerometers to determine torque and horsepower to the wheels. I took horsepower data from 33 different "dyno pulls" and correlated the horsepower with ambient air temperature data (gathered from local weather stations). I was surprised to see how much ambient air temperature affected wheel-horsepower numbers. Here are the results:
1. Decreasing air temperature by 1 degree F will result in a wheel horsepower increase of 0.475 hp.
2. The equation of the trendline that describes horsepower as a function of ambient air temperature is Y=-0.475x + 216.08.
3. My car pulled 211 hp on a Dynojet dynomometer (for a comparison)
4. The trendline shows that a bone stock Cobalt will make 216 hp to the wheels at 0 degrees F, 202 hp at 30 degrees F, 188 hp at 60 degrees F, 173 hp at 90 degrees F, 164 hp at 110 degrees F.

Now you will have a good idea how much more horsepower you will be making on the cold winter mornings. My "butt dyno" didn't lie. Our Cobalts make quite a bit more hp at low ambient air temperatures. Now you know how much more hp...

Enjoy
Eric (aka Micro)

http://www.forums.gtechpro.com/viewtopic.php?f=36&t=109

 

Makes perfect sense. Denser air = more power, like how altitude comes into play with power.

 

that would be great if our cars were n/a, but with an ss/sc ambient air temps dont mean a whole lot to us, what you need to corelate off of is iat2 temps. there is no real set or average value for how much the temp changes between ambient and iat2. being able to average this and come up with a value of how much HP and TQ will change with iat2 value it would be very helpfull for figuring out what cooling mods can actualy do for you.

 

iat2 is based off of iat1 though... if the blower doubles the heat of the charge(made up number btw)...then cooler charges are exponentially better for making HP.....then you can throw in the fact that the cooler ambient temps will also yield cooler coolant temperatures through the heat exchanger, and reduce IAT2s versus IAT1s

 

I want to know how you got the gtech to see the RPM on this car.. mine won't do it!

 

After I attempted to calibrate the rpm signal, it prompted me to select from one of many options for the calibration. I believe that I chose option #16. I have a capacitor installed for my sound system. Since the Gtech uses the change in voltage (through the cigarette lighter) to determine rpm, my capacitor may be the difference between my car and yours. In 1st gear, the rpm signal can be irratic, but it is perfect in 2nd, 3rd, and 4th.

 

I'll try it!.. Thanks!

 

Dude, you said nothing that we don't already know...

... DUH,

 

LMAO...he just used like 5 sentences to say that cooling mods=less heat soak/more power

 

It's reclaimed horsepower it's not more horsepower. It's actually really cheap to add temperature reducing mods (ie ventilation mods) to your car just there's more room for it in the redline bay versus the cobalt bay. Actually that's what I'm working on right now when I get to it.

 

i said something that sharkey apparently didnt know...
excuse me for trying to educate the uneducated...damn

 

my car is a completely different animal when its 20 below

 

Yea, nothing like ripping down the street on a winter morning. My buddy who I drive to work notices he gets pushed further back in his seat on a chilly morning as well

 

I always hate hot humid days , my car feel's like **** . I love 40f low humidity conditions . I think humidity plays a big part too, not just temps.

 

humidity doesnt really do anything. Humidity makes humans hot because we cool ourselves through sweating. But the moisture itself wont hurt at all. in fact, high humidity is akin to water injection with a SUPER tiny nozzle

 

Humid air is less dense than dry air thats why it effects performance.

 

I will try to run the numbers tonight and see if there is any correlation with humidity and horsepower.

 

Before I get into the details, here it is in simple terms:
1. Horsepower increases with increasing humidity (0.4192 hp for every % increase in humidity)
2. Decreasing ambient air temperature by 1 degree F will result in a wheel horsepower increase of 0.475 hp
3. If you know humidity and temperature, you can more accurately predict horsepower
4. The equation to predict horsepower when you know humidity and temperature is shown in the details below

I ran the numbers and I am very surprised by the results. The correlation between temperature and horsepower had an R^2 value of 0.3534. For those who haven't had statistics in a while; the higher the R^2 value, the better the correlation between the data sets.

When I compared wheel horsepower (measured by Gtech Pro RR meter) with humidity, I found that the correlation was quite good. In fact, humidity alone was a better predictor of horsepower than was temperature alone (according to the statistics of my data). The R^2 value for the humidity to horsepower correlation was 0.5887. The equation to predict horsepower (Y) with a known humidity (x) is Y=0.4192x +165.17.

Since both humidity and temperature had a good correlation with horsepower, I decided to build a model to predict horsepower (knowing both humidity and temperature). My predictive model had an R^2 value of 0.779 using multiple-regression analysis! I compared the predicted values (based the weather data) to my actual horsepower values and I couldn't believe how good the correlation was. The equation to predict horsepower Y, knowing humidity (H) and temperature in F (t) is Y= -0.141162261t +0.357602193H +177.7047366.

 

Is there any way I can get access to the iat2 temperature data without HP tuners?

 

yea...any scan gauge...aeroforce interceptor, MSD dashhawk, etc.