I've previously read that turbo cars perform better with the AC on due the cooling effect. Specifically with the 996tt, do you think it's faster with the AC on? Would this only apply to warmer outside temperatures (>70 F)?
My butt dyno tells me the car pulls harder with the AC on, especially when it's warmer out.

 

One advantage of having the air on is that it cools the fuel line on hot days which
is a good thing.

At the TX Mile, the Mad Professor told me to run with my AC on...it sure was nice
and comfortable going down the air strip!

MK

 

In most cases under heavy load the ecu will shut off the AC. Basically, when driving the car aggressively the AC will more or less be inoperable.

This is something that can be "tuned" in the ecu upon customer request.

 

+1. Akram (a Porsche tech) described the fuel system to me once. The fuel is indeed cooled by running the a/c, and the cooler is located in the circuit before the fuel returns to the tank. So sitting at idle for a while will lower the fuel temperature in the tank. The process is not fast if your tank is full, and it is even slower if you are on the throttle as less fuel is returned to the tank. And for those worried about parasitic compressor loss, at wide open throttle the a/c compressor cuts out.

 

Interesting, that's good to know! ... to think I've been sweating away with the AC off with the good intention of reducing stress on the car

 

I just put some ice cubes in my tank.
(How about dry ice?)

I would love to hear the data from a dyno run back-to-back
with room-temp gas, and then a tank-full from cans chilled
in a cooler at freezing... I believe that gas is formulated
differently for different parts of the country, to ensure good
vaporization at the ambient temperature, and other things.
I wonder if our tampering might have some bad effect?

Joe

 

Really the "turning it off" notion to race was for back in the day, cars now will automatically shut it off when driven hard (full throttle etc). You'll notice the a/c vent air go from cool, to warm.

edit - opps kinda misunderstood, I thought you were talking performance, air on/off, on turbo vehicles yes it can help as stated above will help lower line temps, not a night/day difference.

 

Is it the AC that cools the fuel... or does the fan that drives external air into the AC condenser also cool the fuel?

If so, turning on the fan WITHOUT turning on the AC compressor would seem to maximize power at all throttle positions. (Ah, yes, this would be a mod.)

 

It is the a/c system (condenser/compressor/coolant) that cools the fuel. Pop the engine hood and look for the round aluminum canister with the two aluminum tubes on it, just to the right of the Y-pipe. That's the unit. Run your engine, then turn on the a/c and watch it develop condensation.

It will not effectively cool fuel when you are on the throttle. It only cools the fuel returning to the engine (excess fuel not used by the injectors). When you are heavy on the throttle, the injectors spray more fuel and there is not much leftover to cool (especially with the 100%+ injector duty cycles some of these guys are seeing!).

 

Todd K and Steohen K both explained to me how having the AC on can theoretically result in more hp. However in back to back 60-130 runs there was no diff. I prefer to sit in the hot Texas sun w/ the air conditioning on, however.

 

AC ON certainly helps my performance....

 

Great Info I was melting on my car on the track...

 

Doesnt running the ac on the track leave water on the track?

 

A very small amount...not enough to be a hazard. If you are sitting in one spot ofr a while it will leave a puddle.

 

You learn something new every day. Good thread.