c993k

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

ca993twin

Chris,

Thanks for researching and posting Ruf's answer. I'll have to consider putting mine back on if I ever do any "banzai" runs.

tj90

Thanks for the info. I love the litnany of qualifications you list - I could almost see you zipping up the flame suit as everyone replies to you about being being unsafe, out of your mind, whatever.

I would like to remind you, that according to my tests, the head temps will be a whopping 5-8C higher at idle ONLY with the tray installed. At speeds above 10 mph, no significant difference in temps.

Maybe its a RUF conspiracy when they replied with basically "leave the tray on". Maybe they know that you will heat soak the valves and you will be back at RUF rebuilding the motor.. Be careful what advice you take!!!

....All in good sarcastic fun!

InTheAir

Interesting stuff. Thanks for the report.

jackb911

So, if this is the case, why didn't 934's and 935's have an undertray?

Bull

Or any 964 Turbos, Cup Cars, 993 Cup Cars, any factory race cars of any era?

BS!

Scott 1996 993c2

Interesting.

Scott

Dr. No

Just a guess, but maybe because they have enough other aerodynamic stuff on them (like splitters and big ole' wings) to counter the destabilizing effect of no tray with lots of downforce. The stock 993 just has the little spoiler. I wouldn't be too quick to call BS on this one.

c993k

They had HUGE wings that put about 400lbs of downforce at 100mph
plus a different era.
Chris

Bull

So, now the tray is supplying "downforce"?????? Alois Ruf aside, how many stock bodied 993s are attaining speeds near 200mph, or anything near any Ruf Porsche?

Lets don't kid ourselves that we are all in this together with Ruf! But if you want to help with the noise problems in your area, keep the tray on.

c993k

Read the post again, NOT TRACK SPEEDS!!! We're talking top speeds
Again BIG WINGS created more downforce than any little engine tray could do
Chris

ca993twin

Bull,

"So, now the tray is supplying "downforce"??????"

No. It sound like the theory being proposed is that the huge "wings" are supplying so much downforce on those cars that the possible instability caused by the lack of the undertray is unnoticed. That's the way I'm reading this. How did you get to your conclusion?

c993k

I noticed no difference in noise with tray on or off
all I hear is the Fabspeed Super Cups~
Chris

Bull

Ok, so it isn't relative to any tray removal discussion here.

Dan V

Whats the 0 - 170 mph time for NA 993?