Rick

My 2.7T/Tiptronic now has 1300 miles on it, and I have noticed from the beginning that it sometimes seems faster and with more power than at other times. I have not considered the differing circumstances. I live in central Indiana, so it has always been relatively cold when this has ocurred.

One of my other cars is a Corvette with a Lingenfelter 383 (highly modified, 400 HP, 450 lb-ft torque, mid to high 12's quarter mile ET), a torque monster if there ever was one. It is normally aspirated, but it too feels stronger at times, and weaker at other times. It seems to be related to outside temperature: during a hot summer day, power is down a little, but on a cool night, it flies! Same phenomenon, I presume.

John

What you are experiencing is a phenomenon common to turbocharged engines. They produce more HP in cold weather than hot, this being a result of the higher density of cold air. More air, means more fuel can be burned which results in more power.

Jim Selders

You're experiencing one of the rules of the physical world: gas is more dense at lower temperatures (PVT = K). Cold air has more oxygen density, thus it's a miniature turbocharging effect.

This is true of all internal combustion engines, turbo or not.

One side-effect: at the same time you have more power at cold temperatures, your tires have less grip - a tricky combination!

Jim

Bill J

I posted about this same topic last night. I have noticed this also and especially with the APR ECU upgrade. This is what I have surmised; When the car is at rest but the engine is running (like at a stoplight, or in traffic) the engine compartment and especially intercoolers get hot. When you accelerate hard after this the intake air from the intercoolers is much hotter than normal. The knock sensors sense knock so the ignition is retarded thereby stopping the knock but also reducing power. After driving on the highway for a while the intercooler would cool down and the power gets better.

Low octane fuel would presumably have a similar effect except it would not get better until you got better fuel. The effect would be more pronounced with a chipped engine because there is more boost and so hotter intake and more retard to stop detonation.

s moyle

Lemme get this straight, you have a Lingenfelter 383 and you dont know that colder denser air produces more HP?? Turn in your keys.

Rick

Regarding S Moyle's comments: I was simply adding to an already existing thread about varying performance. Of course I understand the temperature effects. You will note that I pointed out that my 'Vette is affected by outside temperature, while my A6 is affected even with constant and cold outside temp(underhood temp is more important on a turbo engine). I have been a mechanical engineer for 25 years, so I understand internal combustion ("heat") engines. Therefore, my keys will remain with me, thank you very much.

s moyle

Guess thats why your post I responded to didnt make any sense. Anyway, Ive figured it out for you. When you drive the 2.7T after your 383, its slower. When you havent driven the 383 in a while, its faster! Why not take it up to Johns shop and leave it there for a while, god knows what he could think up for the 30V! SM