The typical GT Oil Cooler location is in the front which then exits the air under the car. The air exit is obviously not ideal.

So I'm thinking about putting a cooler in the Rear Panel, fed by a NACA Duct in the Rear Trunk lid. Whatcha Think?

The Cooler would be kinda like this but in the center

Click to view attachment

I don't think the air flow will be enough
frontal "ram" air is much more significant.

I've had friends with coolers in that location and they didn't find enough air
(tranny coolers only)... one guy even went through multiple naca ducts trying to increase air flow.

your also adding weight to the worst place on the car

Mount it in the front and duct through the fender wells. You could even direct the air to the brakes. The air comming off the oil cooler is still cooler than hot brakes.

The air above the rear lid is pretty low pressure. You'd probably have more luck running fans on it in that location.

Check out this thread and this thread and this thread

WOW is that a nice lay-up. Nice glass work.

I still really like Chappy's setup where its integrated into his Ducktail.

I thought that was his intercooler not his oil cooler.

Depending on how much you are trying to cool, my setup put a setrab cooler under the rear trunk with an electric fan. Fan turns on when temps hit 180. My oil temps on longer drives dropped from 250 to 210 when I am pushing the car and 200 when I am cruising. No Naca duct or other visible change and no cutting to the tub.

It is, but regardless it would work the same if either was mounted there, no?

The hot air would need to be vented out of the trunk, however.

I no i've got no business posting on this , but


why does no one utilize moder porsche boxster style air inlets


instead of two radiators at each front bumper corner , ala the boxer ,


just use a modifed front facia with a oil cooler in that same location .


and why don't the watercooled guys use that setup also , instead of

1 big stupid ugly . radiator , ???????

I'm not convinced the air pressure differential is enough to effectively cool the oil. I'm a little concerned about Chappy's air temps too. Chappy's rear spoiler surely helps create a lower pressure zone behind it. Carr may need a similar spoiler to capitalize the pressure differential as well. Although it may still need a fan. In a hot climate, hammering on the car for an extended period of time will cause max oil or air temps to either cooler. The key is having enough Delta T through the cooler.

When I had my old 914 in college (90s) I put the AA cooler in the right rear fender-well.
That thing is cavernous, I think I could hide a body in there ;-)

Anyway, obviously, there is very little air flow in there so it probably wasnt working too well.
Fast forward to now. I was going to do the exact same thing for my racecar build, but with a duct to pull in air.
Turns out in vintage racing, I am not allowed to penetrate the body panels for cooling ducts (unless they were there from the factory) so that is not an option.

For racing clubs that DO allow ducting, I see many places that air could get into the right rear fender.
Just one example is the stupid hole in the door/door-jamb.
I think a plexiglass passenger window with a molded duct could pull more air than required and dump it into a shroud in the fender-well.

Another option is a down facing duct under the car, but then you have to worry about picking up debris or pebbles.

Stu

As a v8 guy with a narrow body car, I like front location for the radiator since it puts some weight in the front trunk that help offset the added weight in the engine bay and provides a nice balance.

Two smaller radiators say in some fender flares may work, I've seen some nice ducts, but exit air would be a new study and it would make for a lot of plumbing.

Draw is the important factor whether we're talking about radiator or oil cooler and Porsche used the under front exit that worked for the 914 GT well without an airdam because it had the flow across the exit. Even the special edition airdam didn't extend as low in the front to provide airflow under the car to draw air out the bottom of the engine bay.

NACA ducts only really work in laminar air flow, by sucking off the boundary layer.

e.g. - 931 hood duct works.

Once the flow has separated, shape isn't nearly as important - you might as well just use a straight-sided duct. Having the exit in a nice low-pressure area helps, of course. A ducktail spoiler with a bit of wickerbill would help, but you have to like the look of the spoiler. (I figure the clean tail was good enough for GT's on the Mulsanne at Le Mans...)

Did the same thing, had the same results. Of course, I have a cut front trunk for the A/C condenser which has an electric fan.

This may be helpful. Scroll down to the bottom and look at the 2010 year.
I added it today.

http://www.cassidy-online.com/porsche914/a...aids/index.html

Thanks an interesting study and raises a thought that I've had for the hot air exit for v-8's that I've not seen talked about here.

I've not tried this because there's no going back for me if it doesn't work, but according to the wind flow study above it looks like taking out the hood seal from above the wheel wells aft to the corner of the hood, and removing the seal track would be a good low pressure exit since the airflow over the car seems to be diverted buy the windshield and accelerated at that point.

Anyone tried that?

Neat idea. But i bet you would start fighting rust and horrible rattles.
Not that 914s don't already rattle.

Zach

Rattle? Mine doesn't rattle. It talks to me. It speaks. It sometimes lies to me. I put new tires on it today and it thanked me by developing an exhaust leak. SIGH!!

To continue this interesting discussion, why is it (in the original post) that you think the location for the GT-spec air exit under the front of the car is non-ideal, TC? It seems ideal to me.

My logic is that the airflow near the front of the car underneath should draw the air out through that vent by the Bernoulli principle. Put another way, that principle tells us that a pressure differential must exist across the vent below the car when there is perpendicular fluid flow.

I suppose the case could be made that the flow under the car is likely rather turbulent, but if the vent is installed close enough to the front there shouldn't really be that much turbulence there. Even if a vortex developed under the car (which I think would give it noticeable lift characteristics on the front which I'd not heard of happening with the 914 at reasonable high speeds [i.e. below 140 mph]), it would still be such that fluid flow is perpendicular to the vent itself regardless of direction, going forward or backward relative to the vent. Hence, it's still Bernoulli principle, and still a "suction" or more correctly a pressure differential that pulls flow out through the vent. I have to add that at high speeds having a suction underneath the vent might be a moot point given the driving force across a front-mounted oil cooler being dominant.

The principle would work anywhere there is such flow characteristics, even near the back of the car (without having to have the special-case NACA duct). The problem with having a cooler further away from the front is the obvious loss of fluid flow across the cooler itself that one gets in the front of the car (assuming the car is moving of course).

Just thinkin' out loud.

Sidebar: I have a small point to consider about the difference between an oil cooler and an intercooler: in one case, the air is removing heat from oil and in the other it is removing heat from compressed air. Obviously the type of material the cooling fins and tubes are made of is a big factor, but the point remains that one is removing heat from oil and the other is from compressed air. A brief search confirmed my suspicion that the specific heat capacity of most common oils (likely to be higher for motor oils) is about twice that of air under STP. When air is compressed it's c(p) as well as it's thermal conductivity will go up a bit. What I mean is that air is much more effective at removing heat from compressed air than oil, all other heat transfer parameters being equal. In other words, there may be more more important factors in installing intercoolers (such as length and complexity of plumbing and distance from the compressor impeller and the intake manifold) vs. the same for moving oil around. I would wager its cheaper and more effective to route longer oil lines than longer intercooler lines, so oil up front and intercooler near the motor seems to be the way to go, by my logic.

Ye gods, I'm glad I typed all that before the cold meds really took effect.

Yup, and thank God for spell check.
Took me a couple of times to read what the hell ya wrote.
My meds has kick in

Air exiting under the car is never ideal.

Care to elaborate?

Air under the car means lift. Air on top of the car is downforce. Simple really.

Understood, but my thoughts were based on existing flow for the car's design. Not much needed for what I was talking about. Certainly an oil cooler vent will not change the airflow under a 914 to the extent that it lifts. Doubt the GT would have been so successful otherwise.

I believe the GT was successful mainly because it was a Mid-Engined car. The guys at Porsche were throwing things at it without really knowing the outcome - ie the Rear Strengthening Kit, it really doesn't do much. Same for boxing the Trailing Arms. A good correlation is the 917 that was made in the era of the 914. Yeah it would do 250mph, but couldn't keep going in a straight line. The Porsche Drivers were truly scared to drive it. Porsche tried Long-Tails, Short-Tails, Kamm-Tails. It took them a long time to figure it out and by the time they did, the 917 was obsolete.

In this case ( the Front Oil Cooler), they needed to cool the Engine ( it is called Air-Cooled, but is also Oil-Cooled) so they stuck an Oil Cooler where it would be in the Wind.

However a 914 is really a Very Unstable car at High Speeds. Approaching 120mph, the Rear of the car wants to lift off the ground.

Interesting points. Thanks guys for indulging my engineering geekiness.

And Ground- Effects is sucking any air out from under the car and creating Wings/Foils to creat downforce.

Jim Hall of the Chapparals is a Genius - The Sucker car ( that had side pieces that went the ground to keep air out and 2 Fans powered by a Snowmbile engine to suck out air), Huge Wings that moved, I believe he was the 1st to put louvers on top of the front fenders to relieve air pressure. He also used Sequential Automatic Trannies to save time during shifts - all of this was in the 60's. They Banned some of his cars because they were so radical and Too GOOD

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Here's one for the engineers; How much lift does a GT oil cooler cause and, at what speed?

...and; would the air hitting that portion of the front bumper have gone over or under the car naturally (or both)?

My car is suprisingly stable at 120mph. Don't ask how I know I do have a shitty wing on the back. It is lower than ideal but I can feel a remarkable difference at speed. My radiator is vented through the fenderwells with the intake in the bumper. I have an air dam and the car is very low. Minimal air is traveling under the car.

Click to view attachment

Some and when going fast.

Just to add another thought.
We put a cooler in a horizontal position, strapped to the engine mount bar (on a /4 motor)
Passenger side, no fan assist.
Did a great job of keeping the temps down.
Interesting air flow in that area with the two little plastic flapper pieces in place on the bottom of the firewall.

Rich

Yes, it would go under naturally, unless you have an air dam across the front of the car.

So for a car without a front air dam it really doesn’t matter where the air comes out, bottom, sides, or top. Drag (which makes you go slower) created by the opening up front for the oil cooler is much more of a concern really.

http://www.cassidy-online.com/porsche914/a...side_top_up.WMV