85euro928

Greg,
Try not to hold back so much

Carl,
Have you heard of any failures of the block or drive line due to the solid mounts being used?

I really don't want to have to replace the solid MM but I will if I need to. I have a pan gasket replacement project schedule for this winter so the MM replacement wouldn't be too much of an issue. Anyone else care to chime in?

smudaaar

I have them....also put in solid trans mounts....the 928 drives like a race car now! car lunges off the start and shakes a little more. LOL

928mac

I remember this kind of discusion last year and I decided to go with a solid rubber mounts when I did the Mbearings.
I don't think it changed much from my stock mounts other then they were about 3/4 inch higher.
The engine sits solid and dose not move around (some say thiers dose)
I don't notice any extra viberation or Drone.
They must be strong because i do not baby it.

So far I have been very lucky, and very happy with all the recomendations (here) and parts that I have bought.
I would never install a solid metal mount.
OH Thats A Lie.
I had a 650HP cutlass that I use to 1/4 mile (ran the solid plate mount accross the frt of the engine)

mark kibort

why wouldnt I chime in.
Yep, 20 year old motor stock mounts , on many of the race/street cars I support or own, and no issues at all. In fact, I like them a little compressed, as they lower the engine center of gravity.
I would have a hard time understanding how that could be good, due to the fact that all the vibration and force would be directly on the engine mounting ears. this might be one of those solutions looking for a problem.

Randy V

That's gonna leave a mark!

ROG100

Brad,
We are talking about solid aluminium MM's not solid rubber.

Greg - say it like it really is - I agree.
Roger

surfridermason

Howdy Mr. Tyson


I put these solid aluminum mounts from Carl in my '90 gt. They're fantastic if you like it raw.... If you're a little light on your feet and looking for a little cushion under you- Well.... I don't know why. And there isn't much to comment on for the negative other than nothing.

I also put in the solid tranny mounts. THEY DO MAKE NOISE, it transfers the whine of the gears right into the car, but you don't notice it if you're constantly punishing the gas pedal

GregBBRD

Good that someone with money, to replace pieces, is testing this stuff.

The 944 GTR's, which used solid mounts, would literally rip the welded ends right off of the 928 torque tubes, used in those cars....and those were chrome moly tube frame cars, with very little flex. Regular maintance was to inspect the bell housings and torque tube for cracks. They did use the stock aluminum motor mount that went from the engine to the frame....these broke like they were made from glass.

All the 951's that we saw with solid mounts on both ends would either crack the transmission or engine bell housing....100% of them!

In case you haven't looked, the engine, torque tube, and transmission are all solidly bolted together on a 928...there are no "flex" joints. Now you have taken that whole "assembly" and solid mounted it into a chassis.....that flexes so bad that the doors are hard to open, when the cars are on a lift! Where does that "assembly" flex, when the chassis flexes?

Don't need an SAE magazine to figure this one out....it doesn't flex. It torques on the bell housings and the torque tube....which will crack or break.

Pay little or no attention....I'm just saying....

GregBBRD

Everything I have to say about Carl is always "sugar" coated....Rennlist won't let me post what I really think.

See post #23 and think about what you are doing and the forces involved when that entire assembly is solid mounted. Something has to give/flex, as the chassis flexes over bumps.

Changes need to be thought through and logically used/not used. There's always someone out there selling "snake oil". And there is always people willing to buy that "snake oil." Been going on, literally, for centuries.

Perfect example, for the 928s, is front sway bars. 100% of the cars equipped with stiffer front sway bars are going to crack the chassis and rip the sway bar mounts off. It takes a couple of years for the metal to "work harden" and the cracks to start appearing...but they all do it. Once that metal is work hardened and cracked, there really isn't enough welding that you can do to fix it....but we try really hard to fix them....and bolt on a stock front sway bar, when we are done.

We call this "job security".

Maybe I should be thanking Carl.....

namasgt

What is the whole purpose of using solid mounts?
Why was Porsche using them on their race car when stuff was braking?

Hilton

Thanks Greg for this insightful post.

Its obvious once you point it out, but it hadn't occurred to me that the entire drivetrain is mounted on rubber at the front and rear, despite the fact that I recently replaced both sets of mounts.

Makes good sense.

GregBBRD

So, Porsche wasn't directly in control of the chassis/construction. They did work on components, but did little work on the car itself. I'd guess that Dave Clem (the chassis builder) tried the stock mounts and determined that they would not hold up to the twisting torque of a 675hp four cylinder engine. He then simply used the "flexible" arms that mounted the 944 engine and attached them to the chassis. Remember, these were very low production number vehicles, with relatively large racing budgets and relatively large amounts of factory support.

With Porsche handing them stacks of replacement torque tubes and aluminum motor mounting arms, they probably didn't get around to thinking about alternative materials to build mounts out of. They had plenty of other things to figure out...like trying to make the engines run for an entire race.

The cross drilling of the crankshafts came directly out of this program. We drill our stock 928 crankshafts to the designs that were used in these engines. To study the different versions of crankshafts made for this program is a real eye opener....lots of custom cranks that seem like they would work perfectly, did not work and were changed.

The changes made in the oiling system, to make the engines live, would fill volumes.

Head gaskets and gasket retention was a huge issue.

The fact that the Alusil blocks would not hold up to the stress resulted in the production of a custom block with removable cylinder liners.

The list is endless.

If I'd never seen what it took to make these 944 engines live, I'm sure I could still work on high performance 928 engines....I'd just wouldn't be as good at it.

namasgt

Thanks Greg, makes sense.
Maybe the solid Aluminum mounts wont cause any problems on 928s making stock HP anytime soon, but over time I can see the vibrations causing crack propagation in drive-train components.

Great information as always.

danglerb

As I read it aluminum motor mounts put chassis stress on the driveline, hp isn't the main factor, its how much twisting and other forces act on the chassis which is being held rigid by the drive line. Potholes, speedbumps, and drive ways being more important than hp or torque.

Just my speculation, but seems like a track car with a full welded cage might have less issues than a street car.

mark kibort

Its just brain dead simple. they are not needed and you are going to stress the drivetrain assembly, that is one solid metal piece, in ways it was not ment to be stressed. If you like the "sound" of a rigid mount, weld some pipes from the drive train and slip them into holes into the chassis . then, you can get the resonance of the engine noise and transmission noise to echo through the chassis. Or you can always remove sound deadening material too. OR, get that little program that goes into your radio that makes race car noise based on RPM.