Porscheologist

The way I see it is that if Bruce Anderson says to remove them, I listen. While you may not see a substantial difference every little bit helps. Heat is the enemy of the aircooled engine. My SC did not have it so why should my 993? Also, unlike the transmission tray I do not recall seeing any scoops to help ram cool air into the engine. They essentially serve no purpose other than a sound barrier. If you do not believe this then maybe you can explain what they are there for?????????

JasonAndreas

The two primary purposes as designed were to improve underbody aerodynamics and for the directed cooling of the engine and transmission. That is the only official engineering data I've ever seen, the designer (Michael Preiss) still works at PAG so theoretically we should be able to confirm that the swiss noise regulations reasoning is an old wives tale that originated in Panorama (I have the issue). Obviously the engineers at PAG would have taken noise abatement into consideration but if the swiss noise regulations were the only or primary reason for the undertray than PAG would have limited the part to Switzerland like they did with certain exhaust parts, the added costs are too high. They also probably would have used a different material.

same here...

ceboyd

wow.. nice heat photo!

ZombiePorsche44

Keep in mind my car has never seen a track day or auto-x and is my daily driver here in So Cal traffic.

I drove my car with the tray from August to December then had Mark @ Black Forest (no affil) remove it in January......I now see engine temps of approx 200 deg when with the tray, I saw approx 210-215 deg. That may not seem like a lot, but I'll take whatever reduction I can get without the expense or hassle of plumbing in another cooler.

And before anyone points out it's winter, I'd remind you that I live in San Diego, Ca where 50 degrees at night is cold.

I also believe that with the tray removed your lower valves will not heat soak as bad upon shut down due to the heat being trapped between the tray and headers/heat exchangers.
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Ever see gears melt in a tranny on the street? I never have, but I've seen and had mine do so when my tranny cooler pump failed in The POC Enduro in 98'.
You cannot compare any temps when track driving with normal street use as track temps in the engine and tranny far exceed any normal street driving.

ZP44

Bull

Somebody needs to tell the Factory Techs that the Swiss noise regs cause for the under engine tray is a "wives tale". I have personally been told that by Factory Techs while in the US doing training. I suspect that is the same place that Bruce Anderson and the Tech Committee rep who was quoted in Panorama received their information.

Take it off, lower the engine temps, and reduce the incidence of leaking valve cover gaskets.

luv2ride

Is an oil cooler actually necessary? with a few de's a year and some around town driving in the north east would it make a difference in engine life? If so than what would be the difference? Mileage...examples... Any one?

Ryan

tj90

Good question - maybe for around town driving maybe not necessary. You already have 12 quarts of oil circulating in an air cooler. The fact that I have 12 spark plugs, 2 oil filters and 8 brake lines tells me that Porsche designed these cars to be bulletproof. I believe Porsche would have put a 2nd cooler in the cars if they felt it was necessary. (Track may be a different story...)

To answer one of the posts above - you dont see air scoops on the tray because it would interfere with the cooling from the fan in front of the alternator. The fan is pushing air forwards and your car is pushing air back. This was the reason why I posted the original question. Porsche could have reversed fan direction, used scoops from below and push air out the rear. But then again, it might interfere with the downforce and airflow on the spoiler.

Wow, I just had a thought - what it all you guys without a tray are killing your spoiler downforce cause now you are picking up airflow from below and pushing it out the rear of the car. The escaping hot air can potentially cause your alternator to fail, increasing the potentials for eddying to occur above the heads, and the warm air is less dense so now your spoiler is not providing sufficient downforce!

I guess you can argue this thing from many different angles and OF COURSE OVERANALYZE this....

tj90

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Lets take a closer look at that photo. Only one exhaust pipe?

It also looks like there are 2 bright spots under the car. My guess is that its originating from the heat exchanger outlets.

Going back to my original post - Porsche designed the tray to isolate the engine from the heat exchanger gases. Without the tray you are mixing outside air with this exchanger gas. Im wondering if you are increasing temps down below the engine without the tray...

Greg Fishman

The car in that picture is a 964.

tj90

Im not familiar with the 964 - anyone want to comment on why there are 2 hot spots...

JasonAndreas

The image was taken of a 964 which is where the swiss noise regulation idea comes from and the patent I posted. The undertray has two small openings for directing air to the cylinder air deflectors (by the oil crossover tubes), there is also another opening at the very front where it meets the transmission undertray.

I'm not sure I understand.

Greg Fishman

Are you talking about the spots on the ground? The catalytic converter runs the width of the rear bumper and it might be the heat radiating from that, or the heat exchanger vents.

If Steve Weiner (head rennlist tech guru and master Porsche mechanic) says to take off the tray due to excessive engine heat and wear, then that is good enough for me. Add to the fact that not a single 993 or 964 race car made had this panel and it is an easy decision to take the tray off. A race team would gladly trade a few hours of engine life for extra downforce if it was possible.

Phil

I'm pretty sure the muffler on a 964 is in the rear of the car. I also think, but I may be wrong....that the muffler would emit heat???

So in theory....if the pic was of a 993 you would have 3 spots? cause I am pretty sure a 993 has two mufflers at the rear of the car, and both emit heat, right?

in regards to the engine tray being off, and the aerodynamics....I took my tray off for one purpose only. I was affraid with it on......that at speed...The rear of the car would lift....from the air travleing under the car....and then the rear would flip to where the front was.....without the tray on....the air has nothing to "grab" onto.

tj90

This is what Im going to do - I will drive my car, temp humidity etc will be logged. I will insure that I drive the same exact course same RPMs as close as I can. I will take my IR gun (accurate +/- 1 C) and measure different locations of the engine. I will do both an idle test as well as driving test with tray on and off. I will post the results/pictures of the test.

The only unforeseen difficultly will be to measure the block under the car with the tray on. I need line of sight for the IR gun to work. Maybe I can drop the tray and quickly - within 15 seconds, measure block temperature.

brucec59

TJ, a couple of reasons you're wrong about the heat tray. 1) My own experience is that I saw an immediate reduction in temps sitting in traffic, where temps are highest, after removing the tray. The engine runs cooler at speed, and I did not noticed any difference in temps there, but I didn't have the car long before I took the tray off to get a feel for temps at speed. 2) You're misunderstanding the airflow. You said that air coming up under the car is pushing up, working against the fan. In fact it's not. The air under the car is flowing past the engine, creating a vacuum that pulls the air down. It's like blowing across a drinking straw and thereby drawing the liquid up the straw.