Cold Weather More HP?
 

So I was reading someone on another thread mentioning more HP in cold weather. So now thinking about it, I was driving the car last week here in Boston when the temp was in the 20s and sure enough I felt more HP. The acceleration was just phenomenal. I didn't think too much about it thinking it may be just because I haven't drove the car much lately. So my question is do you think it really makes so much of a difference? Also, roughly how much more HP do you think it gets in cold weather?

Temperature makes a big difference. That's why you see drag racers icing their intakes between runs. Cooler air is more dense. The more air in, the more horsepower out. My drag car can gain half a second or more in the evening when the sun goes down and the humidity drops. Heat and humidity kill horsepower.

You certainly get increased performance with cold weather, due to the nice dense air the engine is inhaling. Just make sure the motor is at operating temp and enjoy ;)

To calculate the power increase, you must look at the temperature to air density (which is also affected by humidity and barometric pressure) relationship. Standard atmosphere is sea level and 15 degrees Celcius with 29.92 inches of mercury. Its a bit late to be doing the math right now, but perhaps someone in a less intoxicated state can elaborate further from here ;)

Goodnight gentlemen

Patrick

Yes,
Cold dry air is more dense so more O2 per compression = more HP. Somewhere on the internet there is a temp relative hp curve. It is not a huge difference but you can surely feel it. An airplane needs a longer runway for takeoff on a hot day for the opposite reason. Less HP and less dense air to provide lift to the wing.

It's true. Back when I was racing motorcycles, on hot days we'd keep the fuel on ice until it was time to grid up. We estimated a 3% gain in power. It only lasted about 1.5 laps, but that was enough to get a good start in the race.

On all the cars I've had I def. felt the inscrease in power in the winter compared to summer.

To me the most obvious thing is the throttle response. Almost seems like my car has individual throttle bodies when it's super cold and it seems like there's a dead rat in my intake when it's hot outside.

I don't know if you feel it in normally aspirated cars, but any forced induction (i.e. turbocharged) motors, it makes a big difference; hence the intercoolers. Porsche learned this long ago on the 962 program where they went with water to air intercoolers to reduce intake temperatures.

What is the reason non forced induction cars do not have intercoolers?

Gary-

Good question I've never really considered, but I'd have to guess some of the reasons are:

cost added to engine package
added complexity to engine
lack of effeciency in NA motors vs. forced induction

I'm thinking about the induction temperature differences between a NA car @ 20F-110F max range vs. the turbo car working with exhaust which could be several hundred degrees F.

maybe other reasons too.

Gary,

My guess is the temperature of the compressed air (whether turbocharged or supercharged) is hotter than normal. Maybe an intercooler lowers the temperature to a level equal to the air charge of a non-FI engine.

Your question is intersting. Is there a way to efficiently cool the temperature of air on a normally aspirated engine? Other than the traditional cool air intake systems that are so popular maybe there isn't anymore benefit from intercoolers, etc.

Just a guess.

ddb

when i get my best 0-60 times its about 45 -50 degrees, so i think it can make a big diffrence.

This is a great post. I just wanted to point that out.

If only MNBoxster had not traded his Porsche for a Vespa scooter, he would be here holding forth at great length...still can't believe anyone would substitute a Vespa for a Box...

There's a few really good points made here. Forgive me if I go on a little, but I assure you that none of the following was copied from some other web site :rolleyes: .

To start with, as everyone has said, horsepower, or more directly, torque increases with air density. To put is simply, the more mass of air you can get into a cylinder the more force the combustion process will have on that cylinder when it's lit. Typical fluids, air included, get less dense with higher temperature, meaning there is less mass of a given volume as the temperature of the fluid increases. The fuel metering system in the car can sense the increase or decrease in air temperature and volume and adjust fuel flow accordingly, allowing for the proper mixture for good combustion.

Topless, it's true that a turbine engine, such as a jet on an airplane can also make more power under cooler air conditions, but power isn't the reason for the longer runway needed for take-off. That's due to the differences in ar density providing differences in lift. Hotter air, being less dense, provides less lift so the plane needs to be going faster before the lift force is sufficient to raise the plane.

Gary in BR, an intercooler uses outside air to cool the intake charge of a turbocharged engine. The charge has been heated by the act of compressing the air. It is then passed a radiator that exchanges heat with air from the outside of the car to bring the charge temp closer to atmospheric. In a normally aspirated engine, there is no compression of the intake charge so air temp doesn't raise anywhere close to that of a turbocharged car Running the intake air through a radiator that can't lower temps below atmospheric anyway would serve little purpose. Intercooling is a huge airflow restriction that can only be justified if the effects of the pressure drop are offset by the effects of providing a cooler intake charge.

It would continue to get better with lower temps but your tires grip starts to suffer as temps drop and traction suffers.

"There's a few really good points made here. Forgive me if I go on a little, but I assure you that none of the following was copied from some other web site .

To start with, as everyone has said, horsepower, or more directly, torque increases with air density. To put is simply, the more mass of air you can get into a cylinder the more force the combustion process will have on that cylinder when it's lit. Typical fluids, air included, get less dense with higher temperature, meaning there is less mass of a given volume as the temperature of the fluid increases. The fuel metering system in the car can sense the increase or decrease in air temperature and volume and adjust fuel flow accordingly, allowing for the proper mixture for good combustion.

Topless, it's true that a turbine engine, such as a jet on an airplane can also make more power under cooler air conditions, but power isn't the reason for the longer runway needed for take-off. That's due to the differences in ar density providing differences in lift. Hotter air, being less dense, provides less lift so the plane needs to be going faster before the lift force is sufficient to raise the plane.

Gary in BR, an intercooler uses outside air to cool the intake charge of a turbocharged engine. The charge has been heated by the act of compressing the air. It is then passed a radiator that exchanges heat with air from the outside of the car to bring the charge temp closer to atmospheric. In a normally aspirated engine, there is no compression of the intake charge so air temp doesn't raise anywhere close to that of a turbocharged car Running the intake air through a radiator that can't lower temps below atmospheric anyway would serve little purpose. Intercooling is a huge airflow restriction that can only be justified if the effects of the pressure drop are offset by the effects of providing a cooler intake charge."

Could it be?

blue2000s = the NEW MNBoxster??

Yeah I know... which is exactly what I said. :confused:

I never actually thought about it, but now that you mention it. I have been feeling more power since it has gotten colder. Thanks for pointing that out.

It would be interesting to see a dyno test at 70° and at 35° to see if there is a significant power difference.

Oh God I hope not.

The way I read it, it sounded like you were referring to variations in engine power having something to do with the length needed for take off.