It was -8 degrees F here in Chicago on Sat. So I took the car out to see how it did in the cold weather. Could definitley tell a difference. For all you engine techy types out there; What is the real world relationship between intake air temp and HP ?

 

what kind of diffrance did you experiance?

 

a very positive one if he's asking about intake temp and hp relations

 

It seemed like the car pulled harder up and down the rpm range, or maybe I was just dreaming.

 

-8 fahrenheit
you probably weren't dreaming

 

Cold air is more dense than warm, it's natures turbo. It allows more oxygen (higher mass flow, not higher flow, same velocity more stuff) into the intake, re: more power.

 

I've noticed the same effect on my car with the recent cooler weather in CA. Up a certain mountain road that climbs ~1200ft in ~7 miles, where I would normally have to use 2nd gear, with the colder temps 3rd worked fine - car also runs smoother. Could be a combination of cooler engine [radiators work better] and more dense air.

 

In general cars like hot oil and cold air for best performance.

 

I bet cold tyres make it feel faster when you try to brake too

 

I thought I read somewhere that for every 10 deg f you lower the inlet temp equates to about 3 HP gain. As a rule of thumb, anyones guess how that would apply to any given situation. One thing for sure, cooler temps are a step in the right direction.

 

Seems turbo cars are affected much more than NA engines by temperature from my experience.
Had charged intercooling systems on prev turbo cars (not TTs) and the difference is VERY noticeable a very recommended upgrade IMO.
...rob

 

I think turbos are particularly sensitive. When you compress air, it heats up. So, naturally, if you have a delta of 20 degrees - for a naturally asperated engine, that means 20 degrees cooler, and (for arguements sake) +6HP. For a turbo, it's 20 degrees cooler at the intake, but ram that through the compressor, and it cools the charge even more, as it takes less air to get to 2 or 3 bar (or whatever PSI you want). Hence, more bang for buck. Where the manifold air temp on a turbo might be 180 F. When the temp drops 20F, the manifold air temp might be 150F.

True - shade tree mechanics work here. So correct me if the overall idea is incorrect.

 

ZO6Keven,
There's lots of things going on with a turbo or any type of gas compression, the first and most obvious is the heat of compression generated by compression of the air ( think desel ) by the turbo. The higher the boost ( 1 bar = 14.7 psig or 1 atmosphere ) the more energy used to raise the pressure hense the higher the temp generated.

Careful when you make "more" or "less" statements regarding gasses, mass flow is different than flow. Mass flow is temperature compensated and flow is not. Generally speaking, if you raise the inlet temperature the mass flow value would decrease but the flow number would remain the same. Think of it this way, mass flow relates to the actual number of molecules of a gas passing a point over a specific time. Flow is related to the volumetric measure over a given time or the velocity of the gas. I hope I'm not confusing things more than they were before.

Getting back to gas temperature, this is as simple as 1 degree in, 1 degree out. Or, as you raise the inlet temperature one degree the outlet temp wil rise by one degree, independant of what happens to it on the way through the system. If you normally have a discharge temp of 180 deg with an inlet temp of 75 deg and the inlet is raised to 80 deg the discharge temp will be 185, 5 in 5 out.

I really hope this makes things clearer, it's a case of things on the surface looking pretty simple but when examined are not as straight forward as first thought.

 

Corrected HP is around 68 degrees.. say we make 360 rwhp at 68. for every 10 degree drop we gain around 1% hp.

Just before i put my car away it was a realy cold day and I was in my money gear, which is third,
The pull was just nuts... made my a little crazy, it's the kind of pull you feel in your gut.
Now I realy wish I could get another 25-30 rwhp.

 

guys who run at the track with say, WRX's pack bags of ice on the intercooler (in the big huge scoop)
same idea.
If you want another 25-30hp, a light shot of nos would gave you the same cold weather thrills