I tried some searches, but a/c is too short, and "air conditioning and power" didn't come up with anything - maybe my searching isn't too hot.

Nordstern recently (this year) changed passing rules from blinker and windows up to window down and hand signals, and now has changed back. I know that I've seen where windows up and A/C on is more efficient from a mpg standpoint vs windows down A/C off, and I'm wondering about its effect on my power for tracking?

I know that when I did an Audi event last year, the guys were all up in arms about having to have their windows up because it was going to "eat so much of their power". I was tracking my A8L at the time, so I had other things to worry about (although it was awesome, I quickly decided I needed a Porsche - but I digress)

Thanks

John

I have noticed, at normal driving speeds, that the a/c does absorb some engine power -- not a whole lot, but enough to be noticeable. However, at some higher RPM (don't know the exact value, but seems to be over 4.5 or 5K RPM), the a/c compressor cuts off and you get full power. The side-effect is that, if you keep the RPMs up, the inside of the car will get pretty warm.

Thanks Bill. That's interesting, and makes sense.

My Dad posted the same thing on rennlist, and somebody said that at full power, its only comparable to 1.5hp loss or so.

Since I desnorked, I've got all that extra hp to work with, so no problemo

I agree, A/C on will have less effect on power than we think. I have left it on during a track session and did not notice it (untill I was black flagged for dripping fluids).

Having the windows up will have more effect than A/C off, great aero advantage. Not, however very safe track practise. I don't think I would want to have a shunt in a vehicle that would prevent the corner workers from pulling me from the car if required (heaven forbid). That is why all touring (production) car series mandate open windows on the drivers side.

When we had a car hit the tire-wall at Daytona, the only way out was through the window. Not much damage to the car but the front fender prevented the door from openning. If the window was up how would they have got the driver out?

Just a thought;

Stan

See the response in the PCA website under Cayman - Engines.

We're required to have windows up now, without a net. Had a great weekend, and WOW (did I say WOW) does having the window up make a difference - or I'm getting a bit better.

I was getting around a LOT quicker (and on the first day) than the previous time. Only differences were R3 and windows up.

It may be perception, and not reality, but I did my fastest time, 4 seconds quicker this time, AC on, windows up, and again, first day.

Wonder if I could've fit any more commas in that sentence

I do actually have a bit more sound reason for thinking I'm faster with the windows down: I have a spot on the track where I always check my speed to see how I did the previous turn, and its usually 87-88mph if I do it OK. Difference is that at the end of the straight (BIR - fastest track in America supposedly) I hit 135 a lot sooner than I used to, because I had a spot for that too.

John

I have always been conscious on how long I turn my AC on because I notice the lost of power with my previous cars a lot. But, I could hardly feel it in the Cayman S. Maybe it is due to the engine being close to us but, if that is the case, the sound of the lost power should be more evident. right?