keith

Just took a 5 min drive after adjusting clutch free play, and then took a look under the hood (neurotic as I am) and noticed as I was leaning over, supporting myself with my hand over the nose panel above the Intercooler inlet, that the sheetmetal was roasting my skin. Wow. How have I not noticed this before?

As you have guessed by now, this is another of those "is this normal?" questions...

?

OZ951

Can't say I have noticed the nose panel being overly hot. I'll check next time and let you know.

Wayne

White951

I am by no means an expert. I have a 951 also. From what I have learned through another site called www.autospeed.com is that the intercooler acts as a heat sink. It collects much of the heat from the boosted air charge and transfers it to the atmosphere, much like a radiator. The heat you may be feeling is the heat still in the intercooler that is tranfering to the air while the car is not moving. I have never felt there to see how hot it gets. I will try it on the way home tonight.

John

Dave951M

Keith- Glad to hear you're back on the road. Heat from the intercooler is normal. From Boyle's Law, as the pressure increases and the volume remains the same, temp will increase as well. TurboTim may have deeper insight on intercooler temps. I wonder what temp yours is at. Can you get a reading off of it somehow?

Dave951M

jim968

FWIW, any time you compress air, the temp goes up, because you've still got the original amount of heat energy in the uncompressed air in a smaller volume... add in flow friction thru the ducts & transferred exhaust heat picked up in the impeller section of the turbo, and it's gonna get hot.

Not on an intercooler, but I did measure the cylinder head temp on a two-stage air compressor yesterday... on the output stage, it was well over 200 degrees F. Of course, this is putting out 130 psi, not 15 psi or so... but it's also not trapped under the hood of a car.

Jim, taking a break...

IceShark

Jim, the stock 951 intercooler inlet temps are going to be on the order of 250+ F, easy. I know that from measurement. Let that heat soak around for awhile and combine with the engine bay heat and surrounding things will get hot.

One thing you didn't mention for consideration in your shop air compressor analogy, is the volume of air being compressed, as opposed to just pressure build over ambiant, thus total heat generated. I have a SCUBA compressor that does 300 bar ~ 4400 PSI. But it can only manage 80 cubic feet from ambiant to that pressure in about 30 minutes. So a turbo compressing 1 bar above ambiant at many hundreds of cubic feet per minute, your tool compressor some at 8 bar and mine very few at 399, we will all see quite high temperature builds.

The thing to do is get a good alternative to our intercooler as it isn't the best. Though it is fairly good.

jim968

Dan, yep, volume will also matter. And that HP air is scary stuff... I worked for a while ~30 years ago with a 4800 psi system in the Navy... too young & ignorant to be nervous... now I even make my students wear safety glasses working with shop air @ 125 psi.

For short autoX blasts, I suspect it'd help to pack the intercooler with ice if allowed; this worked when drag racing in the '60's (big block Mopars, ice on the intake & around carbs).

Jim, out to lunch...uhhh...wait...

Dave951M

The drag race guys even today use cool cans filled with ice. The fuel lines run through the ice to cool and therefore make the fuel more dense. A more efficient intercooler design would be the ticket here, or, I wonder if anyone has tried to put a set of AC coils in the coils of the intercooler. Now there's a scary thought.

Dave951M

IceShark

Packing the intercooler with ice probably wouldn't work too well from a practical standpoint. Probably would be better to spray the intercooler fins with water mist or inject water mist into the air charge after the turbo to get the tremendous energy soak from the phase change to vapor. Or set up a air/liquid intercooler with a container of ice water as coolant. All three of these are used quite regularly by drag racers who wind up with blown air charges that are cooler than ambiant.

But our car isn't a drag racer and I wish Porsche had left more space to put in a bigger, more efficient intercooler. The intercooler just doesn't have a lot of frontal area and they made it pretty thick to try and make up for that.

I haven't come up with many ideas for significant improvement without puting a new intercooler in front of the radiator. Several people are doing just that but I'm a little concerned about the air flow to the radiator on hot days.

aka 951

What's wrong with the stock intercooler? It drops temps about 130-140 degrees under max boost! People get over 350 hp to the wheels with the stock unit. From what I have seen, the 944 intercooler is one of the best designs to date on a turbocharged production vehicle. Import guys even buy them to put on their Hondas, etc. The only problem may be heat soak, though I'm not aware of anyone with any such concrete numbers on the issue.

Erick

911pcars

Intercoolers get hot not only the pressurized charge air inside but also from heat from surrounding engine parts. Someone mentioned using a water mist to cool the intercooler. Here's a product called MPC that's specifically designed to reduce intercooler and underhood temperatures 15-20 degrees for that extra safety margin. Also cools anything else that's mobile and operates from 12 volts.




Regards,
Sherwood Lee www.SeineSystems.com

White951

An australian sited at www.autospeed.com talks about using a mister on the IC. They have an inexpensive mister that has logic as oppossed to spraying all the time which will empty the bottle real fast or having to press a switch. they specifically talk about the heat soak issue. The latest discussion I read on thier site was a about a subscriber who used it on his Audi S4. Do a search in the tech section.

John
86 951

belz

A racer buddy of mine uses the stock windshield washer reservoir and re-routed the headlight washers to mist the intercooler. He simply hits the washer lever to cool the intercooler.

chuck951

re: rerouting headlamp squirters to spray intercooler.

I bet that would be easy to do on my car. I guess my question is would it make a difference.

How would you use such a thing? Spray down the intercooler before getting ready to take off down the strip. Spray while accelerating?

White951

Good article IMO. CHeck it out.
http://www.autospeed.com/A_0527/P_1/article.html