tj90

Before you flame me - I did do a Rennlist search and other web resources and found that EVERYONE recommends removing engine tray. After a year of ownership, I did for this past weekend track day at Willow Springs. What I found is that oil temps were not any cooler and maybe a little higher. I know there are 100s of factors that dictate oil temp, but I did not see any improvement...

Sitting in the paddock, i thought about this harder and convinced myself that no engine tray may be bad. Heres why:
1) The engine tray keeps airflow under the car from upsetting the balance and flow of the fan in front of the alternator. Think about it, If I have an 80 mph wind blowing against the fan, I am creating eddys and potential hot areas of the engine for proper heat transfer.
2) There are 2 hot air ducts that route below the engine and out the outlets of the engine tray. Keeping the tray on keeps the hot air from entering the engine compartment. Kinda like insulating your air intake on a conventional car.

I am an engineer and actually do CFD thermal transfer modelling for a living. I would love to model the engine, car and simulate air flows to be data driven instead of asking others their opinion. You could imagine the amount of time, energy this would take outside my job so it wont be happening.

For now, I have to trust Porsche that they did this modelling and empirical analysis so my tray will be going back on... I just dont want to upset the manufacturers intentions on how airflow is supposed to move anound the engine. Think about the cooling fan. Im sure Dietrich in Germany slaved on the proper fan design for adequate airflows... My '95 motor has 100k miles and I assume that the engine tray has been on from day one.

What do you all think? I would think that an AUX oil cooler would do more for engine life that removing a cover...

dbf73

Many (most?) would say that the tray is there mainly for noise suppression and to a lesser extent for corrosion protection. Look at the factory based 964 and 993 racecars (the RS and GT2 variants) - did any of those use a tray? Nope. Where performace was the primary criteria it appears Dietrich took a pass.

Greg Fishman

"What do you all think? I would think that an AUX oil cooler would do more for engine life that removing a cover..."

I agree with that point. I think the big issue is the extra heat that is trapped due with the cover causes wear on the valve guides.

ceboyd

also, if you have ever been to the track on a very hot and STILL day, (ZERO WIND/Breeze) then you realize and see all the heat UNDER the car without the tray.

If I didn't go to DEs, I would leave the cover on myself.. but because I do participate in those 20 minute sessions, I figured it best to leave the cover off AND open the rear engine hood on hotter days for more 'air cooling' while parked.

Each to their own I guess...


I've heard repeatedly it was added for NOISE supression.. I wonder if that is the real reason or not?

Steve Weiner-Rennsport Systems

Hi:

The engine undertrays were installed solely for sound surpression to meet very strict Swiss government drive-by noise ordinances. Thats it. No aerodynamic benefits.

All you do is cook the engine and reduce its lifespan when you retain that undertray.

Adding a left-side, front oil cooler is always a good idea on these cars to maximize engine longevity.

InTheAir

AFAIK, the Cup cars never came with them......

TheOtherEric

TJ90-
As you know, you are going against general consensus here. So any convincing argument would have to include a study using a couple cylinder head temperatur sensors, recording temps with and without the tray at multiple road speeds. Without that, it's just pure speculation.

Otherwise, we'd all agree that the aux oil cooler has a huge impact on oil temps. BTDT. Removing the engine tray doesn't affect the oil temps significantly.

But again, neither air flow nor oil temps are really relevant here IMHO. Just the cylinder head temps.

TRINITONY

On a recent tech inspection my twin car same color etc.. was placed on the lift. On removal of the tray quite a bit of oil was found laying on tray, and I think some even fell to the ground. It looked like it was leaking from the valve covers and maybe the filter. Could of been leaking for awhile. The owner was surpised to see the top of tray. If the tray had not been inplace he would off seen the oil leak a lot sooner.

tj90

It just seems weird that porsche would dump hot air ducts right under the engine - hot air rises! Do the cup cars have these ducts? If I designed the engine, I would have extended the ducts another 12" and dump the hot air aft the engine compartment near the mufflers....

Honestly, I dont even know where these ducts are coming from - oil cooler? - but there is hot air that is coming from there...

I have heard the noise law explanation, but honestly, I dont notice a difference. Im sure there is someone with a sound meter... And I dont have varioram.

Opening the deck lid would increase cooling effects of engine at rest for sure.

I wonder if cup cars do not have the tray just to make it easier on the pit crews. Not having the tray allows easy access to the engine and helps diagonse leaks etc faster (as the previous poster indicated). I would think long term reliability is not as much as a cup car - remember, cup cars are rearely sitting in rush hour traffic like a daily driver would be...

Greg Fishman

Hot air rises but your car also moves. I do not believe Cup Cars have these ducts as they do not have heat exchangers.
The sound difference is from the outside, not inside of the car.

Mark in Baltimore

I've removed the tray and installed a Cargraphic oil cooler. In addition to helping with thermal issues, removing the tray makes jacking the car ten times easier, for I, despite my workaholic tendencies, am basically lazy by nature.

TheOtherEric

Honestly, I'm not convinced it's that useful. It never feels very hot up top when you open the decklid, plus our decklids already have huge vents to let any hot air escape. I've seen few people bother to open their decklids. Leaving the key int he ignition with the fan running would do a lot, but will also drain your battery pretty quick...

Bruce SEA 993

There is an engineer in the Seattle area that instumented his 993 so that there were some facts about this subject. I will ping him to see if he has any data. I don't think he spends any time on Rennlist anymore but I will see if he is collected data yet.

Cheers

tj90

Maybe your right - I was assuming that the lid was restricting airflow.

My intention is not to be controversial, but I just did not want to take the standard line about noise laws... Ive never seen anything official from Porsche on this subject, but then again Ive only been in the porsche community for 1.5 years now...

Adding thermocouples to the heads as was suggested would be very interesting - that is something that I can do at my next track event and daily driving...

Mark in Baltimore

I have my rear Moton nitrogen reservoirs mounted above the engine and sometimes open the engine lid to reduce heat soak on really hot days. But even on the hottest days, the canisters stay cool immediately after zipping around on the track, a testament to all of the air whirling around there.