shamelessly cut-and-pasted from the 993 bored ..................


993 Engine Tray Removal Causes Instability at Top Speed~ RUF

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As most of you remember my earlier post about the removal of the engine tray
may have caused my car to be a little bit unstable at high speed.
The thread started to get out of hand and off topic so I closed it.
Since then I have made several runs with and without the tray.
These runs where made in a safe and controlled area.
My results indicate that there definitely is a difference.
This difference is at a speed that 95% of 993 owners would never experience.
I'm talking about all out straight line speed not track speeds.
I have owned two RUF 930's from Germany,
both highly modified and both capable of very high and tested speeds. Both very stable.
RUF tests cars at top speeds well over 200mph all the time and know more
about the dynamics of Porsches than most.
I respect their findings and their solutions so I decided to drop them an email with the tray question.
The answer was;
"We have tried the 993 with the engine tray removed and it was very unstable at top speeds, so we kept the engine trays on all our 993's."
This is straight from,
HP Lieb.
RUF Automobile GmbH Mindelheimer Straße 21

87772 Pfaffenhausen / Germany

Tel. +49 (0) 8265 911 911 Fax: +49 (0) 8265 911 912

info@ruf-automobile.de www.ruf-automobile.de

When I asked if the tray was just put in there for the
strict noise laws, he said "No! The design was to keep bottom of the car
completely flat as many other manufacturers of high speed cars do."

Now with that said, I believe that having the tray off lets the engine breathe better
and it decreases the rate of known failures.
The only real need for the tray should be if you're at or near top speeds.
Chris

 

Chris,
You have a point but I don't buy it that it is necessary. Ruf Racer (roland) used to race his Ruf 993 on Open Track at speeds over 200mph. I don't think he is still around but I don't remember him ever saying he used the undertray. I am going to do a search though.

Not a chance it was km, this is a 800hp GT2,notice how he makes a 996 Cup car seem slow on the back straight.

 

Ruf knows!

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Although I don't really average 205 mph (thanks Steve) I frequently run at 205-210 mph for long stretches. I run with the pan in place because that's what Rul says I need to do. Yes, I presented the standard "heat" arguements to Alois as well as his #1 wrench..Joe Huber.That pan stays!

I know other Porsche drivers that regularly run in the 195 mph range and have reported experiencing an uncomfortable instability with the pan removed.

That's my experience. I certainly plan to run with the pan in place next month in Nevada.

I would guess that Steve's Ruf car would benefit by having the pan removed for around town driving.

When the car is parked after a hard run it really gets hot and the pan traps a lot of heat..enough to "coke" the turbo oil that always spills right before I need new turbos.

Thanks to Kevin..I love the ZC mod's he did on my factory Ruf turbos...don't tell Ruf but they do spool fast. I am hoping to get officially timed at 212 mph in July with my long geared almost stock Ruf Turbo.

Hope this helps.


Cheers

R

 

My $0.02

This may be true at really high speeds and the stock spoiler - but - I've had my 993 with stock spoiler to over 120 without any issue many times (track) and the 964 to 135ish with RSA tail and no issue and with the mombo wing on the current car to 145 and it's been solid (all with no tray).

I agree that things are different at 180-200 or beyond, but even at the track most of us will never see those speeds (and few yet would do it in a car with stock aero).

 

Im keeping mine it keeps the oil off the garage floor

 

Maybe if we drilled the cover out like swiss cheese it would be the best of both worlds and add the extra 10 HP like the drilled airbox

 

I agree that the whole noise thing for the "Swiss market" is not correct... I think J. Reiser of the PCA belabors that point as he tells everyone to remove it. If that were the case, we'd all have swiss gearboxes with the different ratios, too! But we don't, yet still have the undertray. Porsche usually knows what they're doing! And the fact that Porsche obtained a patent on its aerodynamic and cooling abilities seems to counter that, too. I am a proponent of keeping it on - I have it on the race car, and street car.

Tom, I bet your supercar is too low for a rear diffuser to make much difference!
But, it's a free country!!!! Do what you want

 

Please, I want a 964 engine tray. Anybody want to sell their's?

Thanks!

-Doug

 

IMHO Under side airodynamic are very important.removing the tray kill it.Think about the drag caused by undertray removel.The turbulance cause by the open comartment would slow the passage of air under the car.At high speeds this would result in an increase in underside pressure and lift.It also dose a good job of keeping the oil off the floor.There is a mod you can do to get things to run cooler with out hurting airo to much.Just lower the trailing end about an inch.

 

"A redesigned, smooth underbody smooths airflow under the car and reduces drag". From the 1989 introduction brochure of the 964.

 

Just curious. Has anyone ever used the tray, stripped of the
oil soaking, er, that is, the sound proofing material on the
inside surface. I thought about putting mine back, but taking
away a fair amount of the padding/insulation. It seems like it
might regain the aerodynamics but still allow for coolong air
between the engine and the panel. I wonder how hard the
plastic covered pading would be to remove?

 

I always heard that factory 964 based race cars ran with no tray. Can anybody confirm this, eitherway?

 

I'll be with a buch of cup cars this weekend racing. My recollection is that thay do not have undertrays (but I wish I had the air jacks) - I'll confirm.

Ya, I think it's really important to worry about the disturbed air flow that may or may not be caused by a tray being present or not being present as you cruise down the street at 35 mph. It may make a difference at 170, but my point was very few of us will ever do the experiment to see if it matters. For real-life speeds, my observation is it does not matter.

 

I scraped all that junk off of mine when it was off. Car feels like a rocket now! I do plan on removing it from the sides as well when they need to come off for something.

I just realized this is my first post to an undertray thread. I think I spent an hour and a half reading undertray threads one rainy night. Great stuff! How many bolts does everybody have in their undertrays? I think I'm down to about half. Maybe the non-undertray people can sell their hardware to the undertray people.

Chad

 

mine was cleaned off of oil rag material when I bought the car. I usualy take it off in the summer and put it back on during our 70 degree winters