Undertray part 2, real engine temps measured.....
08-12-2003, 11:08 AM
#46
This thread is very funny.
We all own these cars, and they range from 10-14 years old. Many of them have done 100,000 miles plus without a top end rebuild and are still going strong even if they still have the undertray fitted.
If it really contributed to premature valve guide wear, wouldn't there be at least one person on this board that could say "yes, that's why I needed a rebuild at 50,000 miles".
On a new car, I could understand this kind of discussion. But on 14 year old cars with 100K miles on them I think it's hilarious that we're all saying "am I causing premature valve guide wear by leaving my undertray on?". Evidence would tend to suggest not!
We all own these cars, and they range from 10-14 years old. Many of them have done 100,000 miles plus without a top end rebuild and are still going strong even if they still have the undertray fitted.
If it really contributed to premature valve guide wear, wouldn't there be at least one person on this board that could say "yes, that's why I needed a rebuild at 50,000 miles".
On a new car, I could understand this kind of discussion. But on 14 year old cars with 100K miles on them I think it's hilarious that we're all saying "am I causing premature valve guide wear by leaving my undertray on?". Evidence would tend to suggest not!
08-12-2003, 11:29 AM
#47
King of Cool
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Originally posted by Adrian
We just keep going around in circles. We now have people saying id this person says this it must be right (even though said person has never owned a 964) and no evidence and "they said".
This is the problem with these discussions. Oh well this one I am leaving alone from now on. I shall take my 150,000 km never been opened engine with rear cover on and look for more sensible discussions with some technical merit and evidence.
Ciao,
Adrian
964C4
We just keep going around in circles. We now have people saying id this person says this it must be right (even though said person has never owned a 964) and no evidence and "they said".
This is the problem with these discussions. Oh well this one I am leaving alone from now on. I shall take my 150,000 km never been opened engine with rear cover on and look for more sensible discussions with some technical merit and evidence.
Ciao,
Adrian
964C4
This is actually kinda funny going back & forth.
One thing thoug, I never said because Bruce recommends taking it off, it means it's right.
Just said I trust enough his experience that I'm taking (well, keeping) my tray off.
08-12-2003, 11:45 AM
#50
Burning Brakes
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I dont know about the premature valve wear bit, but I definitely have experience with oil temp diffrences with and without the tray - anecdotal data from daily drive to work over last 4 years - 1 year with tray, 3 years without.
What concerns me with a hot engine is heat soak and air intake temperature. My car feels sluggish when it gets really hot on a hot day after being stuck in traffic for some time. However it feels much livelier (same air temp) if it had not been stuck in traffic and got heated up before the highway. Not exactly lab tests but driving my car on a daily basis lets me get to know it quite well.
After I got the Gtech, HP and Torque numbers were consistently lower after the 2nd consecutive run where the engine got progressively hotter. However, 30 mins with the engine lid opened, the power is back up again on the next 2 runs
What concerns me with a hot engine is heat soak and air intake temperature. My car feels sluggish when it gets really hot on a hot day after being stuck in traffic for some time. However it feels much livelier (same air temp) if it had not been stuck in traffic and got heated up before the highway. Not exactly lab tests but driving my car on a daily basis lets me get to know it quite well.
After I got the Gtech, HP and Torque numbers were consistently lower after the 2nd consecutive run where the engine got progressively hotter. However, 30 mins with the engine lid opened, the power is back up again on the next 2 runs
08-12-2003, 11:52 AM
#51
Drifting
Thread Starter
I think it's a good idea to stop with this topic.
Too many people have to many know how, the one on yes, the other on no.
I removed my isolation foam, and let the tray under there!
My car has 155000 km's and runs still great, good starts, good idle, good PPM HC results and low oil use, so...... I leave it as it is designed.
Some day a 10-15000 Dollar rebuild will come, before I purchased the Porsche I spent this amount on every 1 1/2 year buying a different car + service/repairs.
The last two years where the ceapest, 2 Distributor caps, rebuild starter and some service parts.
When the engine holds for an other 2 years I don't complain.
Regards,
Arjan B.
964 C2C 1992 Black
Too many people have to many know how, the one on yes, the other on no.
I removed my isolation foam, and let the tray under there!
My car has 155000 km's and runs still great, good starts, good idle, good PPM HC results and low oil use, so...... I leave it as it is designed.
Some day a 10-15000 Dollar rebuild will come, before I purchased the Porsche I spent this amount on every 1 1/2 year buying a different car + service/repairs.
The last two years where the ceapest, 2 Distributor caps, rebuild starter and some service parts.
When the engine holds for an other 2 years I don't complain.
Regards,
Arjan B.
964 C2C 1992 Black
08-12-2003, 12:43 PM
#52
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I am also still trying to work out how the rear cover can trap heat when heat rises. The prime supplier of airflow in the engine bay is the engine driven fan when the engine is running. Maybe I need more physics lessons.
When the car is NOT running, however, the concept of convection could come in to play to allow that heat to escape more quickly.
Think of the engine bay as a chimney. As that warm air rises from the engine compartment, it would have a tendency to induce a small draft of air from under the car. With the cover in place, that flow would be restricted, but with it removed, it would be less restricted, and thus cooler air would flow up from under the car, replace the warm air above, and thus cool the engine more quickly.
There are commercial HVAC system that use this principle to heat a space without the use of circulating fans.
Of course, all that being said, I seriously doubt that convection or lack thereof is causing any problems for our cars, but on balance I would expect it would have some affect on a stationary car with the engine off.
BGL
08-15-2003, 10:45 AM
#55
Track Day
Amazing thread! 
I am not only an owner of a 964 C2 95000 km (60000 miles), that runs great and with an oil consumption of 1 liter per 10000 km, but I also have a M. Sc. degree in thermodynamics.
From the measurements made the conclusion is easy.
The engine is running hotter with the undertray. But is it to hot?
What is to hot? To hot is when the oil film in the valve guides brakes down and metal to metal contact is established. This increase the wear most dramatically. How to solve it: Use an oil that can work in higher temperatures.
We also have to define how we use the car.
Poser from Miami going 2 mph so everybody sees you. That is a good way to reach high temperatures for the exhaust valveguide area.
A. Because the fan is pushing less air at low revs
B. Because the ambient temperature is high.
The temperature gradient between oil temp and exahust port temp is high. The idle measurements posted confirm this. How to solve it: Do not pose drive or drive traffic jams in high temperatures unless you have an oil that can cope with it. Taking the tray off will help you too.
Autocross. From what I have heard you Yankees drive some kind of parking lot rallies. Low speed high revs on first gear. Lots of air pushed by the fan, but oil temps reach high levels. Not a problem unless you use the wrong oil. The aerodynamic benefit from the tray is neglible in these speeds. Taking the tray off doesnt hurt but it wont help the oil radiator to work better. Use an oil appropriate for these conditions will help.
Driving track events. Keep the tray on, no matter what the ambient temp is. Use an oil appropriate for the climate will sort the problems out. The tray will help your aerodynamics.
All above is for ambient temperatures above 30 degrees centigrade. If the temperature is below 30 degrees centigrade a high quality fully synthetic 5W-40, well 10W-50 above 25 C will probably best, oil is sufficent for club events, with the tray on.
What about cold starts? This is when the valve guides actually do get grinded by the valves. Solve the problem by not taking the Porky to buy the newspaper. The ratio between engine revolutions made with unsufficient lubrication and engine revolutions made total is the grand part of valve guide wear vs milage.
And about natural convection. No such thing occurs around the area of interest, the top end of the engine. Remember that the fan blows 1500 litres of air per second at 6000 rpm. This is a case of true forced convection all around the engine, the exhaust area included. The air through the vent on the wing goes inwards to the engine. The flow is generated by the engine fan, the engine air intake and the wind speed from forward motion of the car.
Conclusion:
Everyone should use the proper oil for the proper climate.
Do not use the car for short runs.
Miami posers, take the tray off.
Everyone else, keep the tray on.
I am not only an owner of a 964 C2 95000 km (60000 miles), that runs great and with an oil consumption of 1 liter per 10000 km, but I also have a M. Sc. degree in thermodynamics.
From the measurements made the conclusion is easy.
The engine is running hotter with the undertray. But is it to hot?
What is to hot? To hot is when the oil film in the valve guides brakes down and metal to metal contact is established. This increase the wear most dramatically. How to solve it: Use an oil that can work in higher temperatures.
We also have to define how we use the car.
Poser from Miami going 2 mph so everybody sees you. That is a good way to reach high temperatures for the exhaust valveguide area.
A. Because the fan is pushing less air at low revs
B. Because the ambient temperature is high.
The temperature gradient between oil temp and exahust port temp is high. The idle measurements posted confirm this. How to solve it: Do not pose drive or drive traffic jams in high temperatures unless you have an oil that can cope with it. Taking the tray off will help you too.
Autocross. From what I have heard you Yankees drive some kind of parking lot rallies. Low speed high revs on first gear. Lots of air pushed by the fan, but oil temps reach high levels. Not a problem unless you use the wrong oil. The aerodynamic benefit from the tray is neglible in these speeds. Taking the tray off doesnt hurt but it wont help the oil radiator to work better. Use an oil appropriate for these conditions will help.
Driving track events. Keep the tray on, no matter what the ambient temp is. Use an oil appropriate for the climate will sort the problems out. The tray will help your aerodynamics.
All above is for ambient temperatures above 30 degrees centigrade. If the temperature is below 30 degrees centigrade a high quality fully synthetic 5W-40, well 10W-50 above 25 C will probably best, oil is sufficent for club events, with the tray on.
What about cold starts? This is when the valve guides actually do get grinded by the valves. Solve the problem by not taking the Porky to buy the newspaper. The ratio between engine revolutions made with unsufficient lubrication and engine revolutions made total is the grand part of valve guide wear vs milage.
And about natural convection. No such thing occurs around the area of interest, the top end of the engine. Remember that the fan blows 1500 litres of air per second at 6000 rpm. This is a case of true forced convection all around the engine, the exhaust area included. The air through the vent on the wing goes inwards to the engine. The flow is generated by the engine fan, the engine air intake and the wind speed from forward motion of the car.
Conclusion:
Everyone should use the proper oil for the proper climate.
Do not use the car for short runs.
Miami posers, take the tray off.
Everyone else, keep the tray on.
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lbpa18 (09-04-2020)
08-15-2003, 11:52 AM
#56
hey, i am a miami poser - how cool is that?
That is possibly the worst conclusion I have ever seen, and of course irrelevant. Everyone will just do what they want anyway despite the proof that was posted by Arjan. Hey, 5 degrees is 5 degrees!
That is possibly the worst conclusion I have ever seen, and of course irrelevant. Everyone will just do what they want anyway despite the proof that was posted by Arjan. Hey, 5 degrees is 5 degrees!
08-15-2003, 12:18 PM
#57
Track Day
Whooo touchy.....
Well maybe I should have written Mexico City poser?
I am sure you understood that I made an ironic generalisation, based on Will Smiths song about this type of driving in Miami. Miami also have a climate that is hot enough for the example. I love to drive my car through the city center after an event before going down in the garage. And if some Porsche owner in Miami want to do the same I dont argue.
I cant see what you refer to by "Hey, 5 degrees is 5 degrees!". Please do fill me in.
About the conculsion, I think it is great because it simplifies without neglecting and extract 4 pages of guessing into 4 rows of understandable advise.
I understand your conclusion. Let everyone do as they please, with or without tray, and not knowing what causes valve guide wear.
Thankfully most of us do not live in North Korea, so we can actually do as we want. Even to tray or not to tray.
Well maybe I should have written Mexico City poser?
I am sure you understood that I made an ironic generalisation, based on Will Smiths song about this type of driving in Miami. Miami also have a climate that is hot enough for the example. I love to drive my car through the city center after an event before going down in the garage. And if some Porsche owner in Miami want to do the same I dont argue.
I cant see what you refer to by "Hey, 5 degrees is 5 degrees!". Please do fill me in.
About the conculsion, I think it is great because it simplifies without neglecting and extract 4 pages of guessing into 4 rows of understandable advise.
I understand your conclusion. Let everyone do as they please, with or without tray, and not knowing what causes valve guide wear.
Thankfully most of us do not live in North Korea, so we can actually do as we want. Even to tray or not to tray.
08-15-2003, 12:29 PM
#58
Drifting
Thread Starter
GUYS, GUYS BE NICE TO EACH OTHER!!!
Tomorrow I make some new measurements on the Nurburgring track.
When it works, I give you the data from under the car and from inside the engine bay [valve head covers]
I plan to make about 10 laps on the Ring, 10 laps on full power, and shall write down as much as possible data measured with a heat gun.
Wait untill Sunday/Monday when I will post the data.
I post on on a other topic, the topic about 'last episode.......
Nice weeken you all
Arjan
964 C2C 1992 Black
Tomorrow I make some new measurements on the Nurburgring track.
When it works, I give you the data from under the car and from inside the engine bay [valve head covers]
I plan to make about 10 laps on the Ring, 10 laps on full power, and shall write down as much as possible data measured with a heat gun.
Wait untill Sunday/Monday when I will post the data.
I post on on a other topic, the topic about 'last episode.......
Nice weeken you all
Arjan
964 C2C 1992 Black
08-15-2003, 03:42 PM
#60
Remarkable
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Arjan, I f you want to make the data relevant you should do more than 10 laps. I'm sure we would all be alot happier if you did, say 50 laps. Then I'll follow your lead. Thanks