Chalkboss

As a regular shadetree mechanic trying to do his own repairs these threads really make my head hurt! Just when I think I have a plan of action you guys throw a wrench into it!

Alan

I'd think so too - these are as rare as hens teeth - 928 Intl just laughs when you ask if they have any - apparently they rarely get cars in with any vestiges of undertrays remaining....

They are a complex shape - but not all of that is required... someone should be able to make versions that are functionally equivalent at least. May not make a fortune but there will be a steady demand. The 928Intl undertray has all the right holes & shapes for the vents - completely perfect - except for the lack of vents to go in it...

Alan

ptuomov

I measured the underhood temperature rise with infrared thermometer two years ago with three combinations: No belly pan, a belly pan without the ducts, and a belly pan with ducts shortened to fit in with the turbos. I don't have the exact temperature changes recorded, but here's what I remember. The underhood temperatures went down significantly when any kind of belly pan was installed. There was a small difference with no ducts vs. shortened ducts, but nothing like the overall drop from going from running without any front belly pan to running with one (with or without the ducts).

My rationale for this was the the air that flows thru the radiator gets immediately sucked under the car if there is no front belly pan. With the front belly pan, air is forced to run further down the engine compartment.

I also rationalized the existence of the large holes in the center of the rear, metal pan in the following way. At speed, the holes create a low pressure zone inside the rear belly pan center. This directs the air flow from the engine compartment above the front belly pan towards the center, parallel to the exhaust. The metal guiding vanes inside the metal belly pan further reinforce this effect. This based on logic only, no direct measurements of the air flow.

I would speculate that from the perspective of the motor mounts those ducts are very important. I would further speculate that nevertheless a belly pan without the ducts is better for the motor mounts than no belly pan.

The car currently has the belly pan with shortened ducts which do direct the inflowing air to the motor mounts.

Since I have turbos, this info may or may not be relevant to someone running normally aspirated.

Caveat lector, as always.

Don Carter

All of this talk about the pan ducts is very interesting. After 19 years of ownership, mostly with an S3, I had no idea there were ducts to cool the motor mounts.

I just checked my 2 S4 pans that are currently off the cars, and one has the ducts and one doesn't. Since they are apparently rare, and some may not have seen them before, here's what all the talk is about...

prescott

Alan-

What MM do you use that survive the 120+ degree heat of summer's in Phoenix?

I've got to do MM, oil pan gasket and fuel lines in the next 3 months and want something that will survive our AZ temperatures!

Brian

GregBBRD

You guys might be a bit a bit more critical about replacing mounts than I am.....which might be the difference in what we are seeing.

I assume that new mounts are designed to collapse a certain amount, with the load of the engine on them....not stay as high as they do when installed.

They, indeed, do this and then maintain this dimension for many years. If you had ever had the chance to see a brand new car at the dealer, you would know that these mounts "settled" before the cars arrived here, for sale.

This initial "dimension change" happens pretty quickly, and does not mean that the mount is worn out or defective.....it means that it has reached the height it is intended to be at....which is just about 1" lower than the Volvo mount starts out at and maintains. (Thus my comment about the Volvo mount being 1" higher than a stock mount, which Roger climbed all over my *** for making.)

Amazingly enough:

1. I do think about this stuff.

2. I've been doing this for quite a few years.

3. I work on more than just a few of these cars.

4. I've been involved with these cars, since they were brand new, in 1978! I was doing performance work on them, by 1980.

I don't pull **** out of my *** just to see if it sticks to the wall.

Bilal928S4

Can you provide a reference point and a dimension that should be checked to see if the motor mounts are healthy or need replacing.

dr bob

So.... Will CF stand the heat there around the exhaust, offering cooling ar to the motor mounts? If so we can make them on easy male forms instead of metal. And they would go a lot faster due to the bling that CF brings to any party or project.

Does the aluminum tray offer the center duct that cools the starter motor?

dr bob

How's this... with new Porsche motor mounts installed:

Bilal928S4

Thanks Dr Bob. Is that after the set that Greg is talking about or just freshly installed?
Thanks

GregBBRD

We overthink and debate everything.

Intentionally.

Everyone on this thread is trying to make these cars better for everyone.....and trying to come up with alternative ideas, as the pieces for the vehicles disappear.

We're trying to improve the breed.

Realistically, if the factory motor mounts were suddenly NLA, we'd all be using Volvo mounts. I'd probably be making up some different mounting pieces, so the engine sat at the proper position.....I'm that fanatical.

jeff spahn

But if you did we would know it was yours because it was always alight upon the wall in a perfectly aligned manner and always be within tolerance on size, shape.

Sorry, you tee'd that one up and I had to take a swing at it.

dr bob

That pic was taken before the car came off the stands. In the years since they were done, they've "settled" less than what's noticeable using the straightedge, maybe a couple mm max. I could probably go shoot a "five-plus years later" comparison pic if it would help, but truly the difference is minimal. There's room for the tip of a pinky finger between the hooks. The mounts I removed, originals then 15+ years old and maybe 60k on the car, were partially collapsed but not completely the way I've seen others since.

DKWalser

The mechanic is well known in the "well respected" sense. He participates regularly on this forum. And, I don't know that the mechanic recommended NOT replacing the timing belt and water pump.

The prior owner claims that he would have had the work done if it had been recommended. I believe that the prior owner believes that he would have done the work had it been recommended. (The prior owner is a multi-millionaire. Based on the other work he paid to have done, I don't think cost was an issue.) I also believe the mechanic would have recommended that the work be done.

So, why wasn't the work done? It may have been nothing more than a communication issue -- which is why I'm not mentioning the mechanic's name. The mechanic may have explained the owner's "options" and what the owner heard was different than what the mechanic intended him to hear. The same thing has happened to me in countless conversations I've had with my own clients over the years. As hard as I try to be clear and precise, clients sometimes misunderstand me. That's not usually the case, but it happens.

DKWalser

Greg - Thanks for taking the time to respond. I appreciate it.