AlexS944

Does anyone else notice a difference in engine response proportionate to either temperature and or humidity? I haven't quite figured out what ratio of temp,humidity and/or pressure makes for the best response?! I can say it hasn't necessarily been cooler days like I would have assumed. Warmer days with perhaps lower humidity may be a good combo?! Once in a while I'll go for a drive and WOW, what a difference!!! Any science majors out there perhaps can shed light on the subject? I am sure its an air/fuel/compression issue but not sure about what the best weather combo would be! No other cars that I have owned were so sensitive to weather changes!

Dave

This was done a long time ago but a search might turn it up. IIRC ad ~1% more hp for every 10 degree (C. I think) drop in ambient temp. Higher humidity might allow for more boost or advance by cooling the charge (read; water injection) but the effect would be negligible and you'd need to burn a new chip every time the weather changed.

Techno Duck

I feel the same thing with my 924S. Some days it seems to run better than others and i tend to atleast think in my head that it runs a little stronger at night than in the day.

I used to joke last winter with my friends during the couple weeks of negative temperatures in the tristate area..."Cold air intakes for everyone!"

dave120

Cold air is more dense than hot air, thus more air molecules get in there at a time when its cold than when its hot. Think of the way intercoolers for turbos work. Turbos blast more air in there but its really hot. They want to get the extra air down closer to the temperature of the outside air, and it makes more power and is safer against detonation with a cooler intake charge.

Yes on a cold day you will make more horsepower, and it's often a good seat of the pants difference, though I'm not sure how much it would register on a dyno. At night when the humidity is lower I notice the engine sounds and feel a lot nicer than in the heat of the day.

AlexS944

Glad to see I'm not alone on this one!!! Can't wait till the real cold weather approaches...ah..just kidding!

M758

Last Febuary I could notice the difference quite clearly.

I was running at a local race track that has 2 to 5 gear acceleration. I clearly found that I was reaching my shift point going in to 5th gear much sooner (5-10 car lengths) in the cool of the early morning seesions. As the day went on it would take longer to get to my 4th to 5th gear shift point.

So even a 20 deg temp change during the day had an impact. It was hard to tell a lap time differnce since the AM sessions were practice and afternoon were qualfying and race and I naturally drove a little harder later on. Plus track temps changed so the grip level changed too. All that muddied the ability to determine real change in lap times.

dgz924s

They sure do run better in cooler temps and humidity. The cars were designed and built in the cooler German climate so it makes sense that they run better when it is cool out here. I think that the aircooled cars were developed just for that reason. It is colder and the need for water cooled is not as critical. My understanding is the car is also best when HOT for performance so a cool air temp plays well for that. Here keeping the cars cool is a issue for us.