DIY Semi Solid Engine Mounts - modded OEM mounts
07-23-2012, 12:12 PM
#1
Racer
Thread Starter
DIY Semi Solid Engine Mounts - modded OEM mounts
My OEM engine mounts were in good condition, but I felt my 2002 996 exhibited excessive play when accelerating, shifting, and transitioning left-right. I was not ready to spend $400 on aftermarket engine mounts, so I made my own.
I gutted the OEM hydraulic mounts, drained the hydraulic fluid, and drilled out the rubber mesh membrane - leaving only bare metal and rubber. I then filled all the voids (top and bottom) with an industrial solid polyurethane of 80A hardness rating. This polyurethane replaces the hydraulic oil in the top of the mount, and fills the bottom void that surrounded the mount stud. This cures for 48hrs in room temp, and is then finished in the oven @ 150degF for 8hrs.
The result is a much stiffer and durable solid polyurethane/rubber mount. Shifting is much crisper, accelerating and downshifting is smoother, and the car turns immediately upon steering input. The chassis sloppiness is gone.
I gutted the OEM hydraulic mounts, drained the hydraulic fluid, and drilled out the rubber mesh membrane - leaving only bare metal and rubber. I then filled all the voids (top and bottom) with an industrial solid polyurethane of 80A hardness rating. This polyurethane replaces the hydraulic oil in the top of the mount, and fills the bottom void that surrounded the mount stud. This cures for 48hrs in room temp, and is then finished in the oven @ 150degF for 8hrs.
The result is a much stiffer and durable solid polyurethane/rubber mount. Shifting is much crisper, accelerating and downshifting is smoother, and the car turns immediately upon steering input. The chassis sloppiness is gone.
Last edited by laz74; 03-11-2013 at 02:13 AM.
07-23-2012, 01:27 PM
#3
Rennlist Member
Interesting. Keep us informed as to the reliability of this modification. Im using the RS mounts which really transformed the feel of the car. Also, off topic, but your coolant tank looks like it could use replacing. Ive never seen one that discolored.
Thanks for posting.
Thanks for posting.
07-23-2012, 01:40 PM
#4
Racer
Thread Starter
The polyurethane is completely encapsulated by the OEM mount: on top by the metal screen, and on bottom sandwiched between the OEM rubber and aluminum housing. The polyurethane is a 2-part liquid that is poured into all voids, forms itself to the mount, and then solidifes upon curing.
Last edited by laz74; 03-26-2013 at 09:47 PM.
07-23-2012, 02:03 PM
#6
Racer
Thread Starter
It has been about 2k miles since I've installed, and I'll be doing autocrosses the next 2 weekends, so I'll take a look at how they're holding up and post some pics following that.
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07-23-2012, 05:42 PM
#8
Racer
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The pics and description are awesome... well done, great post!
Question - What does engine mounts have to do with steering sloppiness or turn-in... unless the engine is a stressed member of the frame (e.g. Motorycles)... or maybe you say now it is after your mod? thx
Question - What does engine mounts have to do with steering sloppiness or turn-in... unless the engine is a stressed member of the frame (e.g. Motorycles)... or maybe you say now it is after your mod? thx
07-24-2012, 09:39 AM
#9
Racer
Thread Starter
The engine and transmission weigh about 700 to 800 lbs, and it is dead weight suspended by 3 mounting points. The problem lies in the fact that anytime the car changes vectors (ie. turning, accelerating, braking), the engine/tranny lag behind the chassis due to inertia. By stiffening the mounting points, the engine becomes increasingly one with the car - the change in direction is more immediate and the car is more settled (stable).
From a performance standpoint, the ultimate solution is solid mounts that create a solid connection between the drivetrain and the chassis (these are available aftermarket, and racecars use them), but this too negatively impacts NVH comfort for a street car. Hence, the happy medium of stiffened mounts.
But this idea is nothing new, as semi-solid mounts have been produced for years. This is just a less costly alternative.
From a performance standpoint, the ultimate solution is solid mounts that create a solid connection between the drivetrain and the chassis (these are available aftermarket, and racecars use them), but this too negatively impacts NVH comfort for a street car. Hence, the happy medium of stiffened mounts.
But this idea is nothing new, as semi-solid mounts have been produced for years. This is just a less costly alternative.
07-24-2012, 12:41 PM
#12
Racer
Thread Starter
That's good to know turbo mounts are solid rubber - I was not aware of that. I would be interested to know the hardness rating of the OEM rubber. It is definitely softer than the 80A poly I poured, so mine should be stiffer than the OEM turbo mounts.
07-24-2012, 12:59 PM
#13
Racer
Thread Starter
I made 2 sets of these and I'm interested to get feedback from a fellow Rennlister that has been using aftermarket semi-solid mounts. If anyone is interested to help me out, pls PM me. I'm located in NYC/NJ, but I am also certainly willing to ship. I will also be at the NNJR PCA autocross this Sunday (Jul 29) at Giants Stadium.
Thanks.
Thanks.
Last edited by laz74; 12-09-2012 at 12:43 PM.
07-25-2012, 12:02 AM
#15
Track Day
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993 375 049 07 should be solid (stock part # for GT2/turbos), I'll admit I've never opened one however. X73, and Carreras appear to have the same part number according to my supplier.
The 964 RS motor mounts are solid also, but they're nearly 3x the price.
The 964 RS motor mounts are solid also, but they're nearly 3x the price.