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Hi Everyone,

I got my car back from my Indy and the clutch feels great! Feeling chipper I decided to mount a set of Rennline Semi Solid Engine Mounts as one of my old mounts had failed and I though I'd like a little more "character" in the car. Installing them was easy and I used the softest yellow inserts. My experienced advise is......DON"T DO IT!!!! There is a more vibration and low frequency buzz below 3000 RPM. Above 3000 the car is intolerable. At 85 MPH the entire car is buzzing and frankly sounds awful. It is nothing like putting a louder street exhaust in it. If you are racing just put the solid mounts in it. If not and you want a little more stiffness get the Porsche GT3 mounts. This is a big mistake if you use your car as a daily driver like I do and even if you do not I can not believe anyone in his right mind would think this sounds good. And by the way my Indy politely warned me not to do it just not firm enough. Anyone want to try them? You can have these, just pay for the shipping. 

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49 minutes ago, Mijostyn said:

Hi Everyone,

I got my car back from my Indy and the clutch feels great! Feeling chipper I decided to mount a set of Rennline Semi Solid Engine Mounts as one of my old mounts had failed and I though I'd like a little more "character" in the car. Installing them was easy and I used the softest yellow inserts. My experienced advise is......DON"T DO IT!!!! There is a more vibration and low frequency buzz below 3000 RPM. Above 3000 the car is intolerable. At 85 MPH the entire car is buzzing and frankly sounds awful. It is nothing like putting a louder street exhaust in it. If you are racing just put the solid mounts in it. If not and you want a little more stiffness get the Porsche GT3 mounts. This is a big mistake if you use your car as a daily driver like I do and even if you do not I can not believe anyone in his right mind would think this sounds good. And by the way my Indy politely warned me not to do it just not firm enough. Anyone want to try them? You can have these, just pay for the shipping. 

 

Congratulations, you have just discovered why these mounts are not for the street:eek:.  If you really want to get the maximum detrimental effect of these things, you should have added a lightweight single mass flywheel.  We had a customer come in with complaints about noise and vibrations in a 996 with the semi solid mounts and lightweight flywheel already installed, and when I test drove the car it vibrated so bad I couldn't see where I was going just going down the road.  And prolonged performance driving use of them can also weaken or crack the engine cases, which is why the RS and RSR factory race cars still carry rubber mounts.

 

Not all aftermarket "performance" ideas are good ones.............

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Congratulations, you have just discovered why these mounts are not for the street:eek:.  If you really want to get the maximum detrimental effect of these things, you should have added a lightweight single mass flywheel.  We had a customer come in with complaints about noise and vibrations in a 996 with the semi solid mounts and lightweight flywheel already installed, and when I test drove the car it vibrated so bad I couldn't see where I was going just going down the road.  And prolonged performance driving use of them can also weaken or crack the engine cases, which is why the RS and RSR factory race cars still carry rubber mounts.
 
Not all aftermarket "performance" ideas are good ones.............

JFP, what is your opinion of those stiffening transmission mount inserts?


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2 hours ago, BufordTJustice said:


JFP, what is your opinion of those stiffening transmission mount inserts?


Sent from my iPhone using Tapatalk

 

Same problem, the stiffer the mount, the more the vibration.

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Same problem, the stiffer the mount, the more the vibration.

Exactly what I suspected. Thank you.


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Well I did not fall for the Light weight fly wheel but I did fall for the transmission mount inserts, the softer ones. The problem I was trying to solve was with rapid transitions in power I could feel the engine banging around back there sort of like driveline lash. Everyone told me it was normal but I had never felt it in the 7 other 911s I had owned. They all said the motor mounts were fine. The one thing that most definitely went away with the stiffened motor mounts was the thunk-thunk I was getting on and off the power. The transmission mount stiffener by itself did not significantly increase the vibration in the car but it did change the sound seeming to lower it in frequency. The new stock motor mounts are on the way and I am hoping they will solve the thunk problem. You can "tune" the transmission mount inserts by trimming back the ears that insert into the slots in the mount. Guess I have nothing better to do.

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