What Motor and Transmission mounts to use, What motor and transmission mounts to use Options

[sithot]

I seem to recall some kind of issue with Webers being blamed on solid mounts?

--DD

Richard Parr does not recommend them for use with PMO's.
5. Solid Motor and Transmission Mounts

I've noticed a proliferation of advertisements for solid motor-transmission mounts for Porsche 911 race cars. I'm sure they sell well because they are CNC machined out of solid aluminum and they look "cool". They are also considered "hardcore". My opinion is that any practical advantage they possess is vastly outweighed by a myriad of disadvantages.

The basic problem with solid mounts in internal combustion reciprocating engines is that they introduce destructive harmonics into the body of the race car and also back into the engine. Everyone has heard the true stories of cracked sheet metal, loosened nuts and bolts, sheared-off exhaust systems and broken engine cases.

The excessive vibration often sticks the float needle valves in carburetors causing flooding and other times aerates the fuel in the float bowls causing a lean condition.

The intense vibration also can knock out components in EFI systems leading to the common full-lean-at-full-tilt-equals-fried-engine syndrome. The additional tooth- rattling vibration and noise increases driver fatigue and the possibility of a crash. And if there is a hard crash, the solid mounts increase the likelihood of catastrophic damage to the engine and transmission.

Given these well known facts, why would anyone use solid mounts? It is because they stop the engine-transaxle unit from twisting, thereby improving shifting. This condition is substantially improved by using the Porsche sport mounts and is totally cured by using a WEVO shifter along with the sport mounts. Frank Eibell in Florida has made and installed anti-torque bars on the transaxle to cure this problem. Jim Patrick in Arizona makes urethane dampened 914-6 conversion mounts. WEVO urethane engine-transmission mounts are available now.

An interesting theory is that solid mounts actually decrease horsepower by forcing the engine to absorb vibrations that would normally be absorbed by cushion mounts. For every power pulse in an internal combustion reciprocating engine there is a reactive pulse responding to inertia, operating in a counterrotational plane. Containing this reactive pulse with solid mounts diminishes the power pulse by adding secondary vibrations. Greg Edmunds utilized this theory in designing motor mounts for his .4cc x 3.75 HP model airplane engines. By trial and error, Greg was able to tune out the unwanted vibrations by adjusting the durometer of the rubber in his composite motor mounts. His engines put out more horsepower and the airplanes flew faster with the cushion mounts! Full size aircraft never have solid motor mounts


As a footnote, not even the viton valves will hold the fuel level in some cases where solid motor and transmission mounts are used. For race cars, we recommend the Clubsport mounts which can be stiffened by modification. WEVO recently developed urethane motor mounts which should be the best of both worlds.

[Larmo63]

I'm going to change out my solid aluminum/delrin transmission mounts to black pillow Wevos.

I think I'm experiencing something a bit too too harsh.

I'll report back my findings.

The ones I have on the car came from Patrick MS.

[GregAmy]

For a track-only car? Solid all the way around. Keeps the drivetrain more positively located.

I'm thinking JWest hard nylon fronts, and Wevo Blues in back?

[ConeDodger]

I was seduced early on by solid mounts. My car is 80% street, 10% track, 10% autocross.

They came back off within a week. Too harsh. (IMG:style_emoticons/default/sad.gif)

Still have them sitting in my toolbox.

[UROpartsman]

So, are you saying that either of the engine mounts that you posted above, could be used for the 914 Transmission? and that they are better options than the 911 motor mount, one (like DRPHIL914 posted a picture of above)?

Sorry, here's that comment, edited for clarity:

*When modified to be used as 914 transmission mounts, 911 engine mounts require the mounting holes in the ears to be filed into an oval shape or re-drilled, do not have the proper anti-rotation pins on the center sleeve, are close but not quite the same thickness, are not the original stiffness (the engine mounts are stiffer), and do not have the same appearance as original 914 transmission mounts, which can be an aesthetic issue in a fully-restored vehicle. However, modified 911 engine mounts were certainly a functional substitute until proper 914 transmission mounts were finally made available again from URO and Porsche OEM.

[GregAmy]

For a track-only car? Solid all the way around. Keeps the drivetrain more positively located.

I'm thinking JWest hard nylon fronts, and Wevo Blues in back?

Here's an interesting data point, Dave: my engine is already mounted solid. As in metal-to-metal. In order to fit the dry sump pump in there, Tangerine had fabbed an engine mounting bracket out of steel plate. Pulled the drivetrain this week and noticed it yesterday...that might help to explain how one of the engine frame mount bolts on the outer end of the crossmember had come loose and the nut departed the car...

I'll go with the Wevos in back.

[Dave_Darling]

My contention is that on a race car, you nut-and-bolt the thing every event. This is one key way that a racer is different from a street car; it is gone through thoroughly very very frequently.

If you don't want to be checking all the nuts and bolts all the time, you'll need to use something that will absorb and damp vibrations.

Sounds like the Wevo type of mounts are a more appropriate option for you.

Solid mounts are absolutely not appropriate for a street car.

--DD

[GregAmy]

Thank you, Dave, I appreciate the advice.

[Ken Mikos]

First drive today after installation of New Motor Mounts, Transmission Mounts and Shifter Bushings. What an improvement, its a different car.

Transmission Mounts and Shifter Bushings were a no brainer but those Motor Mounts, aghhh but well worth it!

Next project, front suspenson bushings.

[UROpartsman]

Excellent Ken, which motor and transmission mounts did you use?

[Ken Mikos]

Excellent Ken, which motor and transmission mounts did you use?

Uro Tranny and Motor Mounts......