Engine cover grill

[S Schroeder]

Hi All-
Does any one know if the screen on the engine cover is designed to let cool air in or hot air out? There is high pressure air coming off of the roof line, but I think it would be low pressure air at the decklid due to the rear window. Any of you engineering types know?
Thanks!
Scott S

[BenI]

The engine grill is designed to let cool air in. Once air enters the engine compartment, it is sucked into the impellar and driven through the fan housing and down around the jugs and heads. This air, now having absorbed some of the heat from the engine, is fed out underneath the car. I can feel it coming out the sides of the car when idling. Thats the basic design, and the illustrates the need for the extremely annoying at times sheet metal to be sealed at all seams. once you start having leaks, the air cooling is less efficient. I hope this helps.

[John Rogers]

Correct, the air is supposed to come in from the top, but the area behind the rear window is in a pretty good vacuum and it gets worse as speed goes up. The way this was solved on my autocross car was to put a deflector at the rear of the targa top (like some mini vans have) to direct air from the roof downward. It was first done by Charlie Wallace in San Diego and will cool and engine a lot. As an example during the Parade my oil temp never got over 210 which is nice. I also saw a couple of other ideas, one was to use a fiberglass scoop that runs from the cover to the top of the Targa top and it worked well too.

[norustscott]

I would like to add note...we are correct in assuming that the grill area is for "cool" are intake to operate the engine and provide cooling. However, with reference to the body areodynamics I believe there is not a vacuum of air robbing the engine of combustion 02 and cooling. The break behind the rear window provides an area of low pressure allowing the engine to draw air more easily. If the intake was on a smooth straight surface, air rushing across the vent would tend to pull air out via a high pressure situation. The fact that the air is disrupted by the notched rear window indeed makes it easier to draw air into the engine compartment @ speed. Again, if your engine is running hotter than normal look for a problem with ingition,fuel system, and properly sealed engine compartment rather than modifications to body designed engineered for a mid-engine aircooled power plant.

[John Rogers]

The slight vacuum idea came about when a test was done a couple of years ago in San Diego on a RSR engined 914 race car that was running hot, even with a huge front oil cooler? There was a marker solution aplied to the rear of the car and it went out and drove fast and the marker in the front 1/2 half of the rear deck lid barely moved at all! When the little deflector was added it was blown all over. You are right about sealing the top of the engine from the heat of the headers and cooling air exhaust and I spent a whole weekend making new sheet metal to seal mine and it runs much cooler now.

[S Schroeder]

Thanks for the responses. Here is the situation. My 2.0 runs between 210-215 on warm days and has been as hot as 220 when pushing it up the mountains (I am in Colorado). The motor is 5 years old and has 6000 miles on it. When I had a factory center console the guage never read above 1/4. I re-did my interior when I flared the car to look like the GT and installed a 911 combo guage (temp/pressure - using the existing 914 sender). This guage is numbered and is where I am getting these temp numbers from. I wanted to be better safe than sorry and purchased an oil cooler that literally looks like it was made by Porsche to fit between the two center grill supports on the engine lid - it really is amaizing how it all lines up. I have the GT engine lid so I figured I was still getting plenty of air flow. The cooler helped (especially in stop and go traffic), but when I would push the car for long periods of time (like the hour and a 20 minute trip up to Vail)the temp would creep back up to 220. So, to make a long story even longer, I ordered a fan from Jegs that is reversable and installed it above the cooler (again, it fit like it's supposed to be there!). When I put up this post I was trying to find out if I should be putting air into the engine comparment or venting it out. If any one is interested (and not asleep from reading all of this) I am taking the car up into the hills on Friday to see how it works. One thing is for sure, the car sounds pretty neat with that fan whirring away! If it does work, my next problem is figuring out how to keep the engine lid open when working on the car. Anyone tried a numatic strut like alot of you have used on your rear trunk lids?
Thanks again for the responses-
Scott S

[Dave at Pelican Parts]

220F is a good temperature for oil. If your car gets that warm only on long uphill pulls, I'd say to leave it alone.

Remember, the oil NEEDS to get above 180F, and 212F is better. The water in the oil will outgas much more quickly at that temperature, and that is the temperature that is considered "normal" for working motor oil.

Don't worry until you start seeing 240F. Some folks don't even worry when they see 260F, but I'd be very tempted to shut the motor down if I saw 250F.

--DD

[djs]

One small tip that I don't see mentioned here is that you should be running the later model plastic air deflectors that attach to the underside of the floor pan at the firewall edge. These were supposedly added by the factory to increase the air flow through the engine cooling tin at speed. I believe they create a low pressure area under the engine at speed that helps to pull more air down through.

If you don't already have these flaps, you can obtain them off of a late junker and attach them with sheet metal screws. My '75 came with them, although I didn't know what they were for until I researched the topic.

Dan