Cars performance and hot/wet weather

[valjo]

I wold like to know, how hot intake air (when it is over 30C outside), and wet intake air impact to engine performance.
I guess my s2 goes slower in hot days ....

[Dr H]

As far as I know:

Hot intake temperatures will bring HP and Torque down. I think torque is effected a lot by heat. I had my car on a rolling road and the ambient temp gauge was reading about 34c. hp was fine but torque was down by a lot.

Wet days are usually good as wet air is more dense that dry air and therefore you get a higher mass for a given ammount of air and your car goes better.

Please someone correct me if I'm wrong.

Leigh

PS I seem to remeber Paul Nugent saying something about the boost control on an S2 being temperature sensetive? Something like the ECU turns down the boost slightly on colder days so the car should drive the same in hot or cold weather.

Do I remeber right or am I taking crap (again)

[valjo]

LPHUK2002 : PS I seem to remeber Paul Nugent saying something about the boost control on an S2 being temperature sensetive? Something like the ECU turns down the boost slightly on colder days so the car should drive the same in hot or cold weather.

i read sth like this on his page too. but i am not sure if it doesnt work good only in theory.

I think wet air reduce hp/torque too.

BTW: how you feel that torque is down whe you drive your car:confused:

[Nero]

Temperature does effect the the outside air. As outside temperature rises, oxygenmolecules are "further" from eachother. So outside air will contain a little less oxygen. So the engine air intake will become a little less effective. Cooler air contains more oxygen. Here in Holland, with a different weather every day, is a good testing area. I believe that my S2 is slower on hot days. Audi says that a standard 3b intercooler cools compressed air back to 60° Celsius.
(it's not my wisdom, this is told to me and not true for sure.)

[Dr H]

I though wet or damp air was better for HP?

As for feeling less torque the car will 'pull' less. Usual stuff like overtaking and going up hills is the places you will notice it most.

My exhaust was blowing and the loss in torque was very noticable, the car just felt weak.

HTH

Leigh

[valjo]

aha thanks LPHUK2002

[audiman]

On a standardish car you may not notice a lot of difference on hot days, but take it from me, on a hot day when the intake temps are high the car feels soo slow. Take it out at night or on a cold day when temps drop, and the car goes like hell.

Typical, when the roads are nice and dry in the summer the car is slower, and when it's ****ing down with rain the car kicks ****.

[Nero]

I agree with Audiman. Cold days are more fun!

[KramRS2]

Originally posted by audiman
Typical, when the roads are nice and dry in the summer the car is slower, and when it's ****ing down with rain the car kicks ****.

Thas why we have Quattro

[dan_b]

Cold air is more dense, therefore more oxygen per gulp, so more power - exactly the same principle as why you have an intercooler to cool the charge...

Damp air is also more dense, and the moisture in the air volume again helping to increase power, I think because it acts as a sort of anti- pre-combustion damping (bit like water injection on some really bonkers cars).

Also, being at a lower altitude does the same, higher air pressure, more oxygen per volume, more power.

I guess the worst scenario is a hot dry day at high altitude with a load of dust in the air = no power!


An effective demonstration of all this is that during the "Heat Wave" here in the UK this summer, aircraft taking off from Heathrow had to carry more fuel, or less weight, in order to make the same journies - on take off, they were burning significantly more fuel due to less power being available in the unusually hot dry air...

[S2central.net]

Actually folks - in standard trim - the S2 chips are designed to reduce boost when atmostpheric pressure is high (eg low altitude). This sounds kinda ***-backwards, but the principle is to allow consistent performance (based on absolute manifold pressure) so that the car is equally quick at high or low altitudes.

There is an additional safety measure which limits boost at very high altitude to avoid over-spinning the turbo when ambient air is dangerously thin.

As regards intake air temperature - the Motronic ECU is also programmed to be very cautious at high air temps to prevent detonation. Naturally the ignition timing is retarded a little at high air temps and that is the major contributor to loss of performance in very hot weather (or on a rolling road in Summertime).

Paul

[dan_b]

Clever things these engine ECUs really.

[A80Avant]

i see...
so is a mere mtm chip giving me only 15hp more and 50nm more(supposedly) a 'tuned' car to notice a lack in performance on hot days?i need to rest my mind ...

[MidnightBlueS2]

On a standardish car you may not notice a lot of difference on hot days, but take it from me, on a hot day when the intake temps are high the car feels soo slow. Take it out at night or on a cold day when temps drop, and the car goes like hell.

Typical, when the roads are nice and dry in the summer the car is slower, and when it's ****ing down with rain the car kicks ****.

Since the power upgrade, temp has been around 30 degrees and there's too much power already !

I'm afraid of winter now !

[Ross]

What power upgrade have you got David? I remember reading that you were recently in Banbury... :mischeif:

Looking forward to seeing what you've done in 3 weeks time