Engine under-cladding

JWPATE · 10-12-2006, 07:06 PM

The Porsche manuals sometimes refer to the engine under-sheet as "cladding, and sometimes as guard". Some call it a shield.

Most experienced owners seem to have concluded that the cladding will increase temperatures in the engine bay and lead to early valve guide wear, at a minimum. But, I know that some also believe it was actually put there to control ground effect pressure at speed, and actually aids in even cooling.

I find myself in the former camp and can only believe that the cladding will raise engine temperatures, and do it under all conditions. Don't need that here in the Nevada heat. My engine is out now for a rebuild and I don't intend to put the cladding back under the engine. Probably will instead put it out for trash pickup.

What I am wondering about is the actual reason for Porsche delivering the cars with that item installed? It does tend to keep things cleaner, and more free from road salt & etc. That can't be justify the expense though. I don't believe it would have been there as a guard either, even though the manual sometimes refers to it as such; and I very much doubt it could have been intended to "smooth the temperatures". Some also have called it a sound guard, which seems to imply that some noise level issue may have made the insulated cladding necessary. Was that it? Or was it put there to smooth out under-car airflow in an attempt to squeeze out another mile or two per hour in published speed rating?

I expect that this issue may have already been beat-to-death several times over, but I cannot find any reference to it in the forum search.
James

AFJuvat · 10-12-2006, 07:58 PM

Was put there to improve aerodynamic airflow under the car.

Haven't seen too much of a difference temp wise with having them on or off here in FL. YMMV

AFJ

bazar01 · bazar01's Garage

I drove mine with and without one month each, no difference in 95 deg weather.
In stop and go, oil temps still got to 9 o'clock mark. with or without.
Highway, oil temp at 8 o'clock. I put it back and winter months is coming.

Bill Verburg · Bill Verburg's Garage

Quote:

What I am wondering about is the actual reason for Porsche delivering the cars with that item installed?

My bet is on sound control

SemperFi · 10-13-2006, 07:59 PM

Hey if you don't want the rear part, the part that covers the engine, can I have it? I'll pay for shipping, I actually think the engineers had something in mind when they put it on, but mine is missing (Maybe really short guys climbed under it and stole it) or the previous owner removed it.

Thanks man,

Semper Fi,

James

JWPATE · 10-14-2006, 09:16 PM

Semper Fi,
I have not yet reached a final decision on whether to continue using that rear undercladding panel. The reason for consulting with this forum of experienced experts was to gain a general opinion on the subject. I thought it would be old news, already settled...........but the response has been otherwise. In fact, most seem to believe that the shield adds no threat of engine overtemp. That opinion of most current members seems to fly in the face of the firm advise of respected rebuilders, such as Henry Schmidt and Bruce Anderson, both of whom advise removing the item. That expert advise is based not upon such owner issues as indicated oil temp. readings, which may not seem to differ whether the undersheet is on or off, but rather, upon the observation of early/excessive valve guide wear on every one of these series engines they have into...every one! For my money it is best to go with the experience and the advise of a true professional.

Yes, there are other possibilities. For sure, these poor air-cooled cars were finally beat out of existance by government regulation. The requirement for all emission polution to be contained and recirculated through the engine must combine with the extreme temperatures of the cat converter. The combination is a great strain even without the tremendious output of the 3.6 displacement as compared to the 2.0 I started with in the 67 car. Just could be that the last of the "true" 911 cars were already beyond it in terms of cooling. I remind others that Porsche was the very last of the line in this regard. VW backed out in 84 with the four cylinder water boxer.

BUT my fellow members, the professionals have taken all that into their collective thinking, a year or ten before it comes up here for discussion.

I have no intention to abandion the wonderful air cooled Porsche cars, that I came to age with. Just want to cut through the various regulations and give my own 964 the best hope for long life.
I wait the imput from others before a decision, but one thing is sure. The panel will never go out for trash pickup without checking with you,
Semper Fi!
James

krauthead · 10-15-2006, 04:20 AM

I'm with AF Juvat on this one. Definitely there for aerodynamics. I can provide a factory quote if you would like. Part of the new C2/4 package. Also contains oil drips nicely. Roy

FRED/LI · 10-15-2006, 05:11 AM

Considering where you are, and the heat of the desert, you need all the available air flow. That shield makes it just a little more difficult to exit the fan's airflow. Coupled with the heat coming off your roads, it warrants removal.
Hope to make a long run this year with mine to your city for a stay with grandkids. Often wondered what the heat would do to the 993. Will find out.
Oh...the reason for the shield was Swiss noise level restrictions.
Aerodynamix? Maybe at top speed. Read somewhere that the race cars did not have them installed.
Another observation...the heat sensored cooling fan operation when the engine is turned off was added when the shields came about. Perhaps they recognized the potential danger then.

Bill Verburg · Bill Verburg's Garage

If it's for aero reasons, Why don't any of the race cars have it

aigel · aigel's Garage

Air flows pretty well at the speed the engine fan gives it. I doubt the panel chokes the air flow. What is the fan speed? 2xengine rpm?

Race cars don't have it so you can access things quickly and see what's going on? Also, they have power to spare, who cares about a bit more wind resistance on the road track?

I decided to keep mine on. The reason is: Have you ever seen an engine of a car that went off in a gravel area of the track (or a road)? Have you seen what happens if gravel spray's the engine at 100mph? Not pretty.

My final remark is that I believe the effect of this panel is overrated - both ways. I believe that it does not make much of a difference in any effect, except for keeping stuff from hitting your engine.

George

BoxxerSix · 10-15-2006, 01:41 PM

Up here in NY summers on my 965 it's a ~30F temp difference in the engine bay with it removed and I've yet to notice any aerodynamic differences on/off.....my two cents if it's welcome

.

SemperFi · 10-15-2006, 02:09 PM

I think you should leave the rear plate off and give it to me

HA!

Anyone know where I can get the inner fenders for my 1990 C2? A good site on the web? I don't want rocks kicking up on the oil lines..

S/F,

James

BoxxerSix · 10-15-2006, 02:58 PM

Quote:

Originally posted by SemperFi
I think you should leave the rear plate off and give it to me HA!

Anyone know where I can get the inner fenders for my 1990 C2? A good site on the web? I don't want rocks kicking up on the oil lines..

S/F,

James

If you don't mind use parts for parts that get abused like that, Parts Heaven or GAD are great places.

JWPATE · 10-19-2006, 07:44 AM

Ah, well it seems there are different opinions as to the reason for cladding the engine. The sound issue seems reasonable, since there is also that side and rear insulation cladding around the engine.
Since there seems to be a consensus that the temperature issue is not much affected by the undersheet, I think I shall continue to use it. If nothing else, I does tend to keep the heat exchangers and etc. a lot cleaner.

James

Bill Verburg · Bill Verburg's Garage

Quote:

Race cars don't have it so you can access things quickly and see what's going on? Also, they have power to spare, who cares about a bit more wind resistance on the road track?

None of the above are true, yes, it allows better access but the reason it was left off is that it didn't make enough aero difference to keep it. Leaving the front spoiler off gives better access too, but guess why it's kept

Garrett · 10-21-2006, 05:06 PM

Porsche did receive a patent for the under-tray design, so there is an apparent aerodynamic benefit according to their engineers.

If it's worth anything, I keep it on my cars (daily driver C4 and race car C4).

Check out:
http://forums.rennlist.com/rennforums/forumdisplay.php?s=&forumid=59

...do a search there and you'll find all the information you could ever want to decide on your own

Garrett · 10-21-2006, 05:08 PM

It's US Patent #5,025,878 on 6/25/1991 if you're interested!

Sonic dB · Sonic dB's Garage

Im putting mine back on...

Part of the reason its there, imo is to protect the engine components.

My car is a little lowered, and I turned into a driveway, and scraped the bottom of the car a little....it ripped one of the air vent rubber gaskets (orange ones) and the air vent came loose and was hanging down.

This wouldnt have happened if the tray was on so Im putting it back on

Sonic dB · Sonic dB's Garage

PS: Ive had it on and had it off driving in heavy LA traffic in heat...and it made no difference in the engine temp either way

Bill Verburg · Bill Verburg's Garage

At least post one of the several posts on the subject

One tray removal thread