Arjan B.

Hi,

Asking you guys what to do.

Driving next week on the Nurburgring, with the experience from last time when the outside temp. was 28 Degr. Celc., engine oil was at full power on max. 10 o'clock [gauge]if I should remove the engine undertray.

Outside temp. never is higher overhere then 35 Degr. Celc.
I know that a lot of you in 'hot area's' removed it already, but overhere we can drive German Autobahn wit speeds up to 280 Km/h, so I think that's when we need aswell a under tray for aerodynamics.

Please give me good reasons for removing it, other then premature valve guide wear.

Thanks,

Arjan B.
964 C2C 1992 Black

John Boggiano

Reasons for keeping it...

1. Protect underside of engine from rocks, bottoming on crests (especially if you have the odd little 'jump'!)

2. Drag factor.

3. It was designed to be there.

Bill Gregory

Reasons for removing it...

1. 3.6L air cooled engines push the limits of what air-cooling can handle, resulting in quicker valve wear. Removing the bottom tray helps additional air get to the engine. Removing the engine cladding surround may provide additional airflow benefits. (Sorry, have to include this in the discussion)

2. Factory race 964's didn't use them.

3. You're not in Switzerland so the noise police won't complain.

4. Another way to lighten your 964

Reason for keeping it on....

1. During winter, to keep road muck, snow, and salt off the engine.

91C2wrencher

Reason's for tossing it!

1. valve wear- blah, blah,blah

2. that thing has to weigh at least 40 lbs!

3. it was only put on to meet noise restrictions

4. I don't recall any of the cup cars running with one, is your car faster than a cup car?

5. being able to inspect under the engine for those little things, like mice nests and accumulated dirt and gravel.

6. Would you wear an insulated jacket on a 90 degree day? I didn't think so.

7. So leave it on, run hot, dirty, quiet, and burn those valve guides.

johnfm

Arjan

you should install the high speed fan switch - it is REALLY easy to do, not very invasive and REALLY cools the oil at the flick of a switch. Yesterday in UK I did 500 miles round trip to Glasgow on Motorway in 32 degree heat - car sat at 100 mph for hours - oil temp never above 8 0'clock with high speed fan on. Never above 9 with fan off. Only needed in the city centre, when oil temp got to ten.

Install the switch - it takes less than 20 minutes.

John Boggiano

O/T...

Arjan,

Isn't it you that has that superb garage?

If so, there's a 'garage' thread in the Off Topic forum that could use a picture or two!

TMH

Maybe not a good analogy. I recall reading a fairly in-depth discussion of this relating to consistency of engine cool-down, and how this was assisted by keeping the undertray in place. Perhaps the better question to ask would be "Would you leave a sauna and go out for a long hike in the snow without wearing an insulated jacket?"

My recollection is also that Porsche recommended removing the undertray only in regions where the temperature was routinely in excess of 35 deg C (Greece, as I recall).

Bottom line remains: Are you smarter than a Porsche engineer?

(I like the idea of the high speed fan switch much better than removing the undertray, but then again I have never had an overheating issue in my C4).

Tom

91C2wrencher

Tom, Some good food for thought there. I hadn't considered the consequences of cool down. However this porsche engineer no doubt has broader concerns than I do, after all his comments are to public at large and could have specific ramafications( just the all cars are tuned for a broad range of operating conditions and aftermarket chips improve on this) and he certainly isn't going to go around and poo-poo anything they engineered. The general understanding remains to remove the tray, albeit if I drove in the winter where large temperature differentials were common and snow and/or ice would be a concern I would likely have left mine on. Where I live in eastern pennsylvania the summer heat can be brutal, often above 85 or 90F and 90% humidity, so when I'm sitting in the middle of a large parking lot doing an autocross I'm little worried about thermal differential and more concerned with heat soak on shut down after a batch of runs.

vove

Took mine off last week and the engine seems to be running a little cooler in hot and humid days. The only thing thats really noticeable is the engine noise. Depending on your environment, to remove or not to remove, everything seems to have its pros and cons.

Kevin

I'm going to start keeping notes on who has there trays on so when they go in for a premature top end rebuilds, they will be so cheerful that they have ran all of those 168mph Aero runs with the aero-tray on. You folks need to put your car on jackstands and crawl under your car with it running and see how hot it gets.

Mark in Baltimore

Take your tray off. Steve Weiner recommends it, as well as many local mechanics. Underside protection? How come the older Carerra's don't have it? I wouldn't (and don't) worry about the rocks. I'm more worried about valve guide wear when I'm cranking the car at the track and on the street.

Cupcar

The factory literature introducting the C4 says the paneling is for the reduction of reflected engine noise. No 911 had it before so there is a multi year experience without it. It was miminimized on the 993 chassis for better airflow. None of the racing variants has it.

I think the case for removing the belly pan is there for me.

So, I removed the belly pan and it's retaining brackets which weighed 11 pounds total.

I also removed the vertical walls which surround the rocker covers and rear of engine which weighed 3.75 pounds. I was concerned that exhaust heat would hurt the spark plug wiring after the insulation removal but have not had a problem as yet.

At a minumum I would remove the foam insulation from all the paneling as this serves as an insulator, besides in my car most of it crumbled away by my just touching it.

Arjan B.

John,

Yes I am the guy with "that" garage......
I will see what I can do on the Off topic forum, I have some problems with upload photo's.

On the undertray part, now I am confused.....
We live in a country where we have a lot of rain during the year. In the winter we have a snow and a lot of salt on the roads....

Can somebody tell me the difference in % how much the valve area will wear more fast with a undertray then without...?

I agree with Tom, are we smarter then Porsche engineers? Why do have the latest modells of the 964 still have them when they knew already from the '89 and younger cars that they will get premature valve guide wear with a engine under tray.

I agree with most of the replies, the guys who have experience on tracks during the years as Bill, Mark etc. that this experience counts. Those people showing the facts.

So I hope the discussion will go on, and I hope I will come to a answer, do it or do it not.

Have a nice day you all,

Arjan B.
964 C2C 1992 Black

Andy Roe

John,

How did you install the fan switch? If it's easy I think I'll give it a try!

Andy

Arjan B.

O.k here is a other main point:

MY 964 is always serviced in Italy, all the years of his life untill 2001.
I have all the invoices from every year.

The Official Porsche dealer in Padova Italia, also know as Porsche Italia SPA [near Venice] did all te care. But the question is.......

WHY DID'NT REMOVE THE DEALER THE UNDERTRAY, I TOUGHT THAT THE DEALERS HAVE ALL THE UP TO DATE IN
STRUCTIONS FOR SERVICE AND REPAIR THE CARS, SO ALSO THE GOOD AND THE BAD HABITS OF THE CAR SHOULD BE KNOW BY THEM.

CAN SOMEBODY TELL ME wHY......?

Greetings,

Arjan
964 C2C 1992 Black