Christer

Lou

Full Moon? That's a pretty good reason compared to mine. Spent over USD3000 or so on buying and fitting a new exhaust system and then found that neither the undertray or the heatshields were 'compatible' with my system. Damn Porsche engineers, when will they learn? My car runs pretty cool though except that I suspect the exhaust may be slowly cooking my HT leads. Apparently this cooking process increases horsepower and torque.

Arjan B.

Louz,

Ok, ok.... I understand. Forget my mis- understanding.

I wish you both a nice Autocross!!

Arjan B.
964 C2C 1992 Black

Flying Finn

I'd remove it (I removed mine immediately) but keep it for winter if you have snow & especially salt.

Since so many good Porsche shop & mechanics recommend to remove it (they've seen plenty of valve quide wear issues etc.) I trust them.
And like some have already mentioned, it's not there for aero or protecting something, it's for sound deadening (and adds weight to almost the worst possible place).

Re: "are we smarter than Porsche engineers?":

Why in earth are we adding cooler fan switches (btw, I have one of those too), changing oils more often than what Porsche recommends, drilling holes to your airboxes etc?
Are we smarter than Porsche engineers?

You know those smart engineers developed great dual mass flywheels, leaky heads w/out gaskets, bad valve quide materials etc.
They don't always get things right, right?

91C2wrencher

Thanx Mr. Finn, well put.

LOU!, LOU! Hey I thought you were my friend? Now you're conspiring against me with some dutchman you don't even know?...:-) and I suspect you'll get plenty of chances to yell "off course" as I rarely can do a run without one! BTW.. did you see that the AX course was moved to a new lot? check the RTR site

Jerry Garwick

In my somewhat demented memory, I remember a mention of it in past tech notes in EXCELLENCE mag which recommended to remove it.

John Boggiano

Christer, and others who might drive on less than perfect roads -

Just as a passing note - I have grounded the undertray quite badly on a Scottish road (it was slightly bumpy and I was going pretty fast). It was a relief to feel it take the hit rather than the engine.

Especially as it wasn't even my car! In fact, the car in question isn't even lowered.

Don't tell the Blue Shadow!

The handbrake turn was good too!

Speedraser

While I don't pretend to know the answer, I'm not convinced that there is no aero purpose to the undertray by the argument that the race cars didn't have one. The race cars ran a big fixed rear spoiler that certainly gives more downforce (or reduces lift more) than the retractable spoilers that the street cars use. It seems at least possible that the retractable spoiler without the undertray provides less downforce than Porsche is comfortable with.

Cupcar

The Carrera Cup racers used the stock wing and no undertray.

I think the 964 does have an effective short diffuser but my guess is that the lift reduction is probably of the order of the change that occurrs between the 964 and 993 which has essentially no diffuser. At 150 MPH the 964 has around 20 pounds and the 993 around 70 pounds of lift at the rear.

Here is a little disscussion on diffusers:Diffusors

Speedraser

Cupcar,

Oops, I forgot about that little exception...

The 993 undertray does appear to have a slight diffuser-like "upturn," though not to the degree that the 964's does. Your pointing out the aero lift figures does appear to support the theory that the undertray does serve an aero function, especially on the 964.

I've heard that the 993's undertray supposedly serves an aero purpose as well, which is the only reason I'm tempted to leave mine on. Do you have any insight into this?

Cupcar

My guess is the undertray is more open on the 993 and probably not worth removing.

I wonder if the 993 Supercups ran the undertray.

Adrian

Dear Bill,
Thanks. I checked when I got home. The M30/69 engine of the 964 Turbo uses sodium filled valves but the M64 series including the M64/50 of the Turbo 3.6 does not but the exhaust valves are made of a different material.
Ciao,
Adrian
964C4

Adrian

Getting back to the subject in hand. I am afraid I belong to the school of thought that say "if you make a statement you have to be able to back it up with some evidence" Now I fully understand that this is not the way of the world today. Freedom of speech often means to people that they can say anything they like and everyone else has to believe it.
I have read some really sweeping statements in magazines about this issue and many others but not one shred of verifiable evidence. Anecdotal, even circumstantial but no genuine "unbiased" facts.

Lets go through a couple of issues.
1/. I do not doubt that valve guide wear has been found on many disassembled M64 series engines. Of course I do not know which ones. 01/02/03/04/50? How many of each? However the more important following questions remain unanswered.
a). What is the definition of "premature" valve guide wear?
b). What is "normal" valve guide valve wear?
c). What is the cause of valve guide wear?
d). Are valve guides expected to wear?


After 30 years in aviation with many long years working on horizontally opposed six cylinder aircraft engines as well as car engines as a hobby I can answer the last two questions.
c). The primary cause of valve guide wear is the valve rubbing against the guide. The prime contributor to this wear is how fast the valve is rubbing against the guide. This is of course RPM.
d). Yes they are this is a mechanical wear issue. Normal wear and tear.

So what are other major contributing factors?
Cylinder head heat
Valve adjustment.

This thread is discussing heat so lets look at this and the impact of the rear engine cover.

The M64/01 engine has an operating temperature range. If your engine remains in this range with or without a rear cover I would dearly love somebody to tell me how a 964 with a rear cover is going to develop premature valve guide wear and the one without the rear cover is going to have normal valve guide wear.

Let us look at other areas of the cooling of the engine. Often referred to on this board as tin ware but really cylinder head cooling airflow baffles are critically important to keep the cylinder heads as cool as possible. These baffles are designed to provide airflow with the rear cover installed. What is the impact around these baffles with the cover removed? What is the impact on engine cooling when the baffles are corroded away, damaged and are removed and not replaced?

The rear spoiler. What impact upon overall cooling does the rear spoiler play. Could we also not say that if we all drive around with our spoilers closed that we are also going to induce premature valve guide wear. This argument in my opinion has the same validity as the rear engine cover issue in the cooling department.

What about using fixed spoilers. Do these spoilers increase or decrease the cooling of the engine?

Heat induced wear in the valve guides is directly related to the cylinder head temperature. This we cannot see. The DME can see it we cannot. All we can actually see is engine oil temperature. I do not regard based on experience the oil temperature as being a fair guide to cylinder head temperature.

Another critical issue I believe plays a significant role in valve guide wear and I am sure will not be discussed heavily is the use of the engine. By this Using the 964 on the street and on the track will certainly accelerate all engine wear including valve guide wear. The M64/03 engine for instance is set to much tighter tolerances, blue printed with all matched components. Funnily enough all the low time engine rebuilds that I am familiar with here in Europe have been on Carrera RSs. Track work, inotherwards racing works the engine hard. I wonder how hours these engines with claimed premature valve guide wear spent on the track. I also wonder how many were and were not fitted with engine covers.

Now we I am sure will all agree that physical movement and the speed of this movement is the primary cause of any mechanical wear anywhere. It is made worse by other factors but the primary cause is rpm. So what impact does the light weight flywheel have. Does the quicker to reach rpm advantage of the LWF induce premature valve guide wear? Does having to pull more rpm to get off the start line induce premature valve guide wear?

Many questions many things to think about and none of us have any concrete answers. None of us can prove or disprove anything unless we do some serious data gathering first. The prime source of this data is the engine workshops who should provide the history of the engine, the history of usage of the 964 and the valve guide measurements along with the factory tolerances. I doubt this will ever happen.

One last thing which has been mentioned before. Many people recommend the removal of the rear engine cover for genuine reasons.
a). It is heavy.
b). It is an oil trap and really crappy when it starts to fall apart.
c). It is a pain in the butt for quick access to the engine.
d). It may slow but not reduce the heat build up when stuck in heavy traffic jams in really hot weather. As long as the cooling systems of the 964 are serviceable I do not see this as any major advantage and may actually not be measurable unless we get two 964s stuck side by side in the traffic and measurements taken.
I would prefer we stick to the truth rather than trying to invent additional reasons to justify our decisions.
I also have some faith in Porsche Engineering that if the rear engine cover or any other component for that matter was going to cause premature failure of any major assembly in the 964 that they would have advised us officially. I could well be mistaken but I am no longer the cynic I was.

Ciao,
Adrian
964C4

Arjan B.

I think I have to agree with you Adrian.

A next issue is that the question is: Why do advise Official Porsche Dealers DO NOT REMOVE THE UNDER TRAY FOR ROAD CARS and the so called Porsche Specialists [often no official dealers, but I believe they have also a lot of experiece an know how] say REMOVE???

Nice day!
Getting 38,5 Degr. Celc tody overhere they say.........

Arjan
964 C2C 1992 Black

Adrian

Dear Arjan,
As with any issue there are many sides to an argument and anything your might write here will find an conflicting answer like "Porsche will not admit they made a mistake" and the list goes on.
The basic point of my post was to throw out a whole bunch of new talking points. In the Porsche world one persons comment can often become the word of "God". An uninformed comment which is said or printed for very different reasons becomes the truth. Many automobile brands suffer from this but because the Porsche world is in scale a small world and with the ease of communication nowadays, these uniformed statements become fact and the stuff of legend. One sad thing of our world today is that far too many people look to far few people for guidance and have simply stopped asking questions. If this person said this, "well he must know so it must be true". When I was young I was taught to question anything I did not understand. Today people do not understand the question. As I have said before and quoting Fox Mulder "The truth is out there".
Ciao,
Adrian
964C4

Ade - C4 91

The "so called Porsche Specialists" also hear the same rumors that we do (to remove the under tray) from various unproven sources.

Perhaps the addition of the under tray in 89 was seen by some specialists as an unwanted variation to a tried an proven method. In other words since the SC and Carrera 3.2 didn't have it, why should this car, and what worked for earlier cars should still work for the C2/C4 - right?. Old ideas die hard.

I think I'll keep mine in place.

Ade.