Jim Michaels

Poll results: 74% of those who support keeping the oil catch tray say they prefer Coke to Pepsi, while 71% of those who support ditching the tray say they prefer Pepsi to Coke. At first I thought the differences in tray opinions might be due to genetic predisposition, but, statistically controlling for a confounding variable, I found a moderately high correlation between tray opinion and which side of the Atlantic one lives on. West siders tend to take it off; east siders tend to leave it on.

Oops. I'm terribly sorry that I was the one to start a 3rd page on the most recent tray discussion.

Adrian

Dear Jim,
I prefer Coke to Pepsi.
The question still remains unanswered and that is what frustrates me. We have all this nonsense about Cups cars not having rear engine covers and this must mean that Porsche made a mistake with the 57000 others. Not one person (including the person who said this in the first place who is not on this forum by the way) has yet presented one scrap of evidence to prove the often written comment that keeping the rear engine cover on causes "premature valve guide wear".
Gee I cannot even get a definition of what constitutes "premature valve guide wear".
For Don who keeps talking about the Cup cars never had covers which is not 100% correct you might be interested that the 993 engines have also been accused of having premature valve guide wear in various publications and 993 based forums. I am also still trying to work out how the rear cover can trap heat when heat rises. The prime supplier of airflow in the engine bay is the engine driven fan when the engine is running. Maybe I need more physics lessons.
Ciao,
Adrian
964C4

PS: I also must have imagined that some of the GT-3RSs at LeMans were running rear covers. Maybe I wasn't there after all.

John Boggiano

Adrian,

That comment puts this all into perspective. And a rather humerous one, at that!



This thread is becoming nearly as entertaining as the one on the Off-Topic forum from the guy who insisted that the 959 has turbochargers which are driven by the camshafts! Mere proof that this is not so was not sufficient for him!

Adrian

Dear John,
I actually have photos of the 959 engine removed from many angles. Taken during a visit to RUF. I kept out of it though. Some people (not on the 964 forum though) just cannot take yes for an answer. I love a constructive argument and even if I am wrong I can at least learn but I cannot argue against statements made without any factual backup without a little frustration and humour creeping in.
Ciao,
Adrian
964C4

Jim Michaels

Adrian:

I think Bruce Anderson was the first person that I read (years ago) saying that the tray probably contributed to premature valve guide wear on engines he had examined with and without the tray. He lives in California; which is certainly one of our warmer states. The question comes around again every few months with the same kind of opinion split. His email address is bruce1485@aol.com (published every month in Porsche Panorama). As Senior Technical Advisor he probably expects to get such tough questions. He's probably not aware of the recent empirical findings posted here.

Speedraser

Don,

I'm still waiting to hear why an undertray would help a water-cooled engine run cooler, as you suggested it would. Please explain. BTW, I'm well aware that a water-cooled car uses water to cool the heads (and block, unless it's a 959 or certain Porsche race cars) and an air-cooled car uses...

Personally, I haven't concluded for myself whether the tray is good or bad. But I don't think its absence on a completely different car -- the 996 series -- tells us much about the tray's pros and cons on the 964/993.

IF it has a negative effect (higher temps) on cooling an air-cooled engine, why, as you say, would it have a positive effect (lower temps) on a water-cooled one? Why would reducing airflow help a water-cooled head?

IF it had an aerodynamic effect on the 964/993, the differently-shaped 996 MAY simply not need it. If it's just there to reduce noise, the 996's sound-insulating water jackets may render the tray moot.

9caregiver

Guys I am not wanting to debate this but..., Todd, I did not say a water cooled car would run cooler. I said it would run cooler than an aircooled car. The shield would have lesser negative effect on the water cars. The water cars do not rely on air circulation as an air cooled car does. The shield traps hot air which surrounds the heads. Removal of the shield allows circulation of air around the heads,case, exchangers ect. Adrian metioned physics, that hot air rises..but where to? The shield effectively boxes and traps the hot air in. The engine fan DOES cool the heads on top but how could it circulate air on the bottom where it is the hottest? Remember the exchangers are in the insulated "Hot Box". To me it is common sense to have more air circulating around the bottom of the engine. Yes Bruce Anderson has recommended removal for years now. I agree with him. You do not have to.

Because these trays were installed in 57,000 other cars does not make them a good idea. Porsche built tens of thousands of cars that were prone to rust before deciding to galvanize the bodies, They built thousands of 911 engines before switching to pressure fed tensioners. They used head studs that were prone to breaking before switching to a better material. Thermo reactor exhaust systems...Ect. All ideas that went into alot of cars before Porsche came up with a better solution. In fact Porsche used a less restrictive tray on the 993 than the 964. If these trays were such a great idea they would be on the new car.

Best,

Don

P.S. I like RC Cola.

Speedraser

Originally posted by RENNMAN:

"...I did not say a water cooled car would run cooler. I said it would run cooler than an aircooled car. "

Don -- now I understand what you were saying...

johnfm

The argument relates to the real difference between oil temps and localised head temps and the transmission of heat to the valve guides. All this after the most basic consideration which, as Adrian states, is 'what is excessive or premature wear'. Until some metallurgists or the designers/suppliers give us an idea of how the material properties of the guides vary with temperature, and we compare that with ACTUAL localised head temps we are all guessing.

Does anybody have any data for oil temps VS head temps, head temps with the fan not running etc - it would interesting to know just how much is OIL cooling and how much is air cooling.


Oh, I prefer coke in my rum!

joey bagadonuts

Okay, I asked Bruce Anderson his take on all this (seriously) and here is his reply:

Hi Joe,

Gosh, it is not my engine. If they want to cook their engines let them go
ahead and do so. Where I was first turned on to the heat problem was in the 1987
new car technical introduction book... they warned of the heat. The panel you
are referring to is a sound panel, designed to keep the noise from reflecting
off the ground. Yes, taking it off will let the engine run cooler. The first
cars to have that were the 1987 Carreras for the Swiss market. And they warned
of them running hot.

The Temperature that we are concerned about here is the cylinder head
temperatures... not the engine oil temperature. The cars from the 964 on had very
efficient oil cooling systems so the oil temp even if affected by the sound
panels will be adequately cooled.

The whole purpose of the undertray under the engine is noise reduction.

Bruce Anderson www.911handbook.com

Arjan B.

O.K. Joe,

Good to hear from Bruce.

O.k., the man has a lot of know how off Porsche, I respect that.

Question: If the undertray is only for noice reduction, why is it not completely filled with foam/isolation material?

Wy is it made so heavy and strong constructed

Are the measured temps on cilinder heads I did last week "The to hot heads"?

Remember the part of the book which tells the story about the Freudenberg Flywheel who had a fault also in engine number getting to LUK.....


Greetings,

Arjan
964 C2C 1992 Black

Flying Finn

Bruce Andersson is not the Porsche god to me but he has so much knowledge about these cars that if he says take it off, I'll take it off.

joey bagadonuts

Just adding perspective. I'm not sure if even Bruce Anderson knows the reasoning behind the design. The comments above are just his recommendation based on his considerable experience with these cars and you may either follow them or disregard them as you please.

And before I forget, thanks Arjan for all the great work. It's much appreciated.

pzull

I think the undertray had 2 main purposes: sound insulation and aerodynamics.

The 964 has the tray sloping upward towards the rear thereby creating more downforce (actually less lift). The 964 actually has less lift in the rear than the 993 which didn't have the sloping undertray. Anyway taking away the undertray will lessen this downforce as the flow becomes turbulent which also increases drag.

But I still have my tray off as the downforce sacrificed is not noticeable to a non racer and I like my engine audible.

Adrian

We just keep going around in circles. We now have people saying id this person says this it must be right (even though said person has never owned a 964) and no evidence and "they said".
This is the problem with these discussions. Oh well this one I am leaving alone from now on. I shall take my 150,000 km never been opened engine with rear cover on and look for more sensible discussions with some technical merit and evidence.
Ciao,
Adrian
964C4