cmoss

Any reduction in temperature is more than made up by all the hot air being generated here.

ps mine's off

tj90

OK - I repeated last nights driving test with the engine tray on. For easy comparison, I relisted the results. Fortunately, ambient conditions are exactly the same as yesterday (thank God I live in San Diego!)

Time / Tray On / Tray Off
00min / 21C / 21C
Start car and idle
12min / 106C / 98C
24min / 140C / 126-156?C
Drive car for 30 minutes, stop, immediately take measurements
54min / 126C / 125C
Stop car and cool down
64min / 117C / 114C
74min / 109C / 106C

After reviewing the results, I wish that I had a better 24min idle temp measurement.

1) It appears that the idle temps were higher (~8C) with the tray installed. Hard to say what is happening at 24min of idle, I think the TC may have been faulty- no tray to keep it positioned on the block and slight movements caused wild temp swings.
2) While driving the car, no difference of temp at the head. Both cases, much cooler than extended idle.
3) Cool down with the tray in place caused head temps to be higher by 3C.

I guess Im eating some crow - removing the tray keep things slightly cooler in idle and cool down.

However, I still have my dignity because the tray does not cause hotter head temps while driving (where I spend 95% of my time). Also, the idle differences measured only differ by a maximum of 8C - about the temp difference between your monitor screen and the room.... It would be hard to convince me that this is responsible for added wear of the valve guides, but maybe Im completely wrong... Leaving the tray on maintains under car aerodynamics and allows airflow around the 993 engine and tranny as Porsche intended by the aforementioned patent cited above.

The take away for me is that there is negligible differences with head temps whether the tray is on or off, but what really generates heat is extended idle. Even without the tray, head temp climb 20-30C higher than if we cruise at 45 mph. This is illustrated by the immediate drop in oil temp just by driving like a grandma after extended idle.

BTW, the 24 min of idle cooresponded to oil needle at ~9pm. I have driven to 9:30 tracking the car and sitting in 405 traffic. I would shut down the motor, or stop it with fan still on, if I got to 10 pm. Keep in mind that you dont hit the red until 11pm. Maybe the motor can get much hotter than we give it credit.

ceboyd

Thanks for the 'test' result.. very nice to see

brucec59

Um... do you have it backwards? Your Tray Off temps are higher. Should your columns be
Time / Tray On / Tray Off?

tj90

Oops - your right. the columns were swapped. I edited the original post so that the columns read Time / Tray On / Tray Off. Thanks for catching the typo.

Monty

Mines done 155k miles with the tray on without engine being opened. I'm leaving mine on ! Results very interesting. One positive for tray being on must be quicker warm up which can only be good for the engine especially in moderate climates.

SR71BLACKBIRD

Good job on the data - Great to know

Scott

TheOtherEric

Thanks for posting all this, it's very interesting. It actually makes me consider reinstalling my cover for DE events in order to get the underbody protection and aero benefits. I say this because there seems to be negligible difference when driving; the car only runs warmer at idle, which is not much of an issue at DE events. The cool-down curve is a little extended but that's largely irrelevant.

tj90

Thanks - Im glad to help. What I find interesting is that the data I collected with and without tray is very consistent with the 964 data collected by Arjans. My understanding is that the 964 engine is different than the 993, yet head temps are very consistent. Arjans conclusion was that heads dont get any hotter with the tray installed.

I also forgot to mention that my original concerns of the heat exchanger outputs right under the engine do not seem to add any more heat to the motor. I measured the output of the exchanger outputs and it was much cooler (70C) than the heads. I am thinking now that the reason porsche vented exchanger outputs to the exterior of the tray was to promote venturi effect that was mentioned above. Maybe they get better flow thru the heater system...

I encourage others to investigate this - the more data the better. It would be great if someone can figure out how to instrument and log data while the car is driving. Maybe some can resurrect old data collected or contact the patent holder Preiss at Porsche AG to comment....

Mark in Baltimore

Great effort, tj! I've been reading this thread with interest.

TheOtherEric

Actually, it would be pretty easy for those of us who use data loggers. There's already an intake air temp that's easy to tap into and log. Unfortunately, there's no cylinder head temp sensor (AFAIK) so that's the tough one.

EDIT: I think actually we have cylinder head temp sensors...see below.

tj90

The challenge with the TC was that there are coolling fins around the head. I could not see the end of the tip and where it was positioned on the head. Between the oil and cosmoline, kapton tape was useless (even after cleaning with alcohol). Maybe cementing it to the cylinder would make the measurement more accurate (conduction vs convection) but I doubt few of us would sign up for that experiment. My TC wire was too short so I had to drive with out the DMM which logs max and min temps. Not quite a logger, but min temps would give you an idea on how cool you can get the head when driving...

I have already been accused of being too **** about this (which I dont refute), so I will let another person on the board continue the experiment.

TheOtherEric

Ok, actually I think our cars monitor cylinder head temps already, but I'm having a hard time figuring out what Porsche calls it. I think pin 45, labeled "ECTS II" and also referred to as "engine temperature" must be it. If so, it would be easy to log intake air temp and cylinder temp to do this study. Can anyone confirm what "ECTS II" is?

JasonAndreas

I tried to locate the older ACO regulations from 91-96 but the web archives only go back to 98-99 which was after the Mercedes flips when the aerodynamic regulations were changed? The IMSA & ACO rules weren't "harmonized" till after Don Panoz got involved after 2000, I'm also looking for the BPR rules. One (not-so-surprising) thing I found, some people had commented that the english translation of the french ACO regulations were not always exactly the same so the french based teams theoretically had an advantage.

Reflection from the sun...

The differences are so minor to be negligible.

With a Bosch Hammer or PST2 you can drive around watching the output from the CHT sensor on the #3 cylinder. My results (as posted last year) were pretty much the same. The temperatures were between 228F - 300F and the oil temperature stabilized ~194F, regardless of ambient air temperature. At a stop light (and at idle) the CHT would initially drop to ~238F and then creep upward. Knock-sensor activity was non-existant.

How-to Add a Cylinder Head Temperature Gauge or use the slightly less accurate Bosch Hammer method.

rkass

TJ, thanks for the effort, makes me step back and think about this again. Assuming that temp is not as big a difference as once thought, the ability to detect leaks vs losing aerodynamic benefit/purpose of tray according to patent is now bothering me. Probably will go with it again and just watch leaking when doing oil changes, etc.

Also want to commend you on ability to take on topic that I sure was going to end up in a flamewar and actually turned out to be civil and informative - good job all around.