SD Porsche Fan

Took the day off so me and my yougest son could hang out and play wanna be racer mechaninc. Replaced a leaking lower radiator hose and took her out for a spin.

It's 36 degrees (F) here today. Spool up was quick and she just took off hell bent for leather! My favorite on ramp seemed pretty short today and she just gobbled up Interstate effortlessly! Boost is lots of fun in cold weather!

So a question for all you dyno heads out there: What difference does ambient temp make in hp and torque numbers?

HIGHBOOST

Well, in an ideal situation for every 10 deg. f cooler the air in the intake tract is, your automobile should create 1% more power.

Jake951

According to the formula SAE uses to correct engine horsepower for temperature, each 5 degree C drop in temperature results in a 1% increase in horsepower. A drop of 5 degrees C corresponds to a drop of 9 degrees F, so what HighBoost has said is essentially correct.

One thing I notice about colder temperatures is that my boost increases, at least with a Reliaboost type of boost controller. Roughly speaking, I see about 2 psi more boost at temperatures near freezing than I do at summertime temperatures. I have to readjust my boost controller with the seasons to maintain more or less constant boost.

Even compensating for the boost change, however, the turbo spool time is MUCH quicker in cold weather. I think that's mostly what accounts for the sensation of more power.

toddk911

This is when us guys down south envy you yankees!!

Down here, we watch the weather intensely to see when some cooler temps are on the way.

This "cold weather" effect seems to get discussed every year as it is always a suprise to get in your car and tear it up when the temps are colder. It's like driving a different car.

Of course, my response is, get water injection. And then you have that same performace all year round. Even if you don't use it to run higher boost or more timing, the gains from just the cooler charge is significant enough.

toddk911

Also, not just the 1% gain for just colder temps, but the effects of the colder air over the IC make gains. The colder temps aid in less heat soak. The turbo is more effecient and thus produces more psi without making any increases in boost settings.

toddk911

When you say 10 degree F drop = 1%, are you referring to ambient drops or intake temp?

TurboTommy

I did a quick calculation and I got roughly 1.7% for every 5 degrees celsius
and yes, on a turbo engine the gains would be more because it goes by the intake manifold temps, which get affected by the IC, where the cooling capability increases in a non-linear fashion as the temps come down.
Also, lower temps provide a slightly better back pressure vs boost pressure relationship, so there's slight gains there as well.
Water injection is not quite as good as cold ambient temps because firstly, evaporated water takes up a little space, and secondly, there's possible tuning needed to compensate for the now colder, moister air, which the engine management didn't know about when it originally sensed the air after the air filter.

Now, too bad the colder days also offer a loss of traction............

hosrom_951

You guys are lucky, it is still getting to be 37+C/99F+ here

newkie

I got 4 degres C here ;D

newkie

Well atleast u dont have to put your cars in the garage for 6 months a year :P

potent951turbo

The last day or so here in SC the temperature has really cooled off and my 951 is loving it. The boost seems to rush in so smooth and effortlessly now.
There is a cold front moving in this weekend that is really supposed to drop the temperature, so it should make for some nice weekend driving.

toddk911

That;s true about the really cold climates that you guys can't even drive the car. As down here we drive year round.

So I guess some give and takes

Yea, I am awaiting that cold front. Although down here we will olny see the low 60's.

SD Porsche Fan

I usually fire it up and take it out on nice days when the roads are dry. This year might be different though as I bought a storage garage on the other side of town and may store it there.

Has anyone thought about a method of packing ice (probably dry ice) around the IC? Probably wouldn't be practical but it sounds like it might work.

toddk911

I have

I have thought about almost EVERY possible way to get the IC/intake temps down from living in FL.

I even considered some how routing the AC lines wrapped around the IC pipe and intake. So when the ac was running, you would have freon cooled lines around the IC and intake.

toddk911

I also looked into getting a fuel cooler. basically an oil cooler for your fuel lines.