Venting unwanted heat: undercar, trunk or wheel well?

[jpnovak]

There have been many documented front oil cooler installs. I spent some time digging through the archives and could not find a thread that addresses the merits and deficiencies of each method.

Let's say you have a front mounted heat source in the trunk. yeah, like a big ol' oil cooler. The large volume of air comes into the front trunk area behind the heat source and is hot. That air has got to go somewhere. Let's say in this car that the aerodynamics are the same in all three installations. Same bumper, same airdam, same frontal area, etc.

There are three places this hot air can go:

1) out the bottom of the car
2) out the hood of the car
3) out the wheel well of the car.

Option 1 is the simplest from a fabrication standpoint. Several places build ducts that can easily be installed. The question is why would you want to put hot air under the car. Well, you wouldn't as it can cause unnecessary lift. Aerodynamics on the front end are important here.

Option 2 is to send the hot air up through the hood. There are advantages here. you can exhaust into a low pressure area aiding the air flow. The hot air is expanding and can (maybe?!) provide slight down-force. Downsides of a hood installation are water intrusion and funny looks when driving down the street. Not so much of a problem at speed on a track.

Option 3 the hot air mostly goes out through the wheel well but some underneath. plumbing could be complicated as you have suspension bits here and depending on brake ducts could put hot air into the ducts. Yes, the factory oil cooler installation is in the front wheel well so this area could already be full of hot air.

The question is: If there are no class limitations where would you install the vent? Which is the best in terms of aerodynamics and keeping good airflow? and more importantly why?

[911pcars]

"Let's say you have a front mounted heat source in the trunk."

For track-only purposes? Then any one of the three work to some extent. As for the most efficient. I'd say the most efficient is when the air flows as straight as possible w/o any turns in the air flow. Thus, the hood vent.

For the street, it depends on what size engine you're trying to keep from overheating. A center-mount oil cooler, even mounted flush with the front bulkhead, can be effective with an engine up to 2.7 l. The middle front of a vehicle is subject to the highest air pressure; it tapers off toward either side.

Anecdotal reports from owners suggests engines larger than 3.6 l require one very large cooler or two fender-mount coolers.

Sherwood

[rattlsnak]

although not the easiest to install, the over the hood method is probabaly the best here, and i dont know what you mean by 'water intrusion', as its not a problem if done correctly, and I got no funny looks, but rather MANY thumbs up signs and much interest, so according to your post, #2 has no downsides,

[jpnovak]

Sherwood, my thoughts exactly. efficiency is what its all about.

Rattlsnak - your green meanie was definitely an inspiration.

Ok I confess. Its not a 911 but its mid engine cousin. Think small turbocharged motor to give away no details. I actually think the hood vent will be the easiest to install. To make it look good is another matter entirely. I wonder what stamped louvers would like like facing backwards up the center of the hood?

[tony9704]

"The question is why would you want to put hot air under the car. Well, you wouldn't as it can cause unnecessary lift. Aerodynamics on the front end are important here. "

Really? Does the heat have any noticable effect on lift?

I've always wondered why the oil cooler is put right in front of one sides tire only. After a lap at the Autocross, my tires temps are quite different. The passenger side never does cool down as it is constantly bombarded with new idling engine heat while in line.

[911pcars]

"The passenger side never does cool down as it is constantly bombarded with new idling engine heat while in line."

Eliminates the need for a tire warmer on that side. Hot tires should provide more grip on the AutoX course, yes? Thing is, you also have 3 tires that are not up to operating temp.

Sherwood

[911st]

Make sure you check your class rules. Our local spec911 class will not allow hood venting because of the real or perceived down force advantage.