So we used 80# polyurethane in the motor mounts. For the positive - throttle response is greatly improved and the car seem much more solid & tied together. There is an improvement in both handling as well as acceleration.

Now for the negative there is a bit more roughness at idle but it is perfectly acceptable. At 3/5's throttle there is more noise and vibration. Above 4000 rpm the engine begins to get a bit thrashy.

No final verdict yet. I have only had time to put a couple of miles on the car and have not taken it to redline or driven down the hwy.

 

Had a little more time behind the wheel so wanted to update my impressions. Throttle response is immediate - there is no delay. I do not have a sprint booster but I think someone commented that one of the benefits was in taking off from the line. The motor mounts have a similar effect.

I mentioned previously that the engine gets a bit thrashy above 4000 rpm. Either I am getting used to it or I my initial impression was overblown. It is a bit rougher but not sure a passenger would really notice and I think it is a decent bit higher in the band than the initial 4k I reported.

I am happy with the poly motor mounts but am still debating whether to try 60# urethane vs. the 80#. I may go ahead and have my shop pour the 60# and swap for a comparison.

All of these impressions are based on ~20 miles total of driving so not a whole lot of seat time.

If you track your car at all I think this is a worthwhile mod. This is not a mod that would drive you crazy or really bother you in a daily driver. The bit of exhaust drone I have on the hwy is significantly more annoying than the motor mounts.

If you decide to pour your own mounts be very exact in your measurements of hardner to urethane. Even being off a small amount can ruin the batch.

 

sounds like a great mod! i have a friend who wapped mounts and he is sending me his to try this out. let me know if you do the 60# as im not sure which way to go

 

I am liking this mod more and more. The car seems much more willing to downshift and much more responsive. On the hwy today is seemed to take less throttle opening to get it to kick down a gear.

Have not decided if I am going to do the 60# or not. I need some more time with the 80# motors mounts.

 

let me know. if you want i can do the 60# when i get the mounts and we can swap them back and forth to see which is better!

 

Would the 80# mounts be comparable in performance to the aftermarket red poly bushings?

With a six-speed, I'm sure this would be a fantastic mod. I don't get much above 4,000 RPM in daily driving unless I'm truly giving it the beans, and at 130mph, luxury isn't at a premuim. A little extra engine vibration isn't going to detract from my permagrin much.

I do notice a bit of "clunkiness" in the 1-2 shift, seems as though the whole motor/trans has a lot of give to it. At 54,000 miles, I'm sure I'm past-due.

 

I strapped down the engine as I broke the motor mounts after 120 miles from swapping in the srt6 engine so had to strap the engine down. didn't want to use the "old chain method" due to noise so cable works well.

 

here's some measurements I took from the new motor mounts that just went in.
You should be able to make up a jig/mould from this if required - I may.

The old mount that was still in one piece required me to slip a 12.5mm (1/2") piece of wood underneath it to make the same dimensions.
I guess that indicates it had sagged 1/2".

My indie mech thought I was crazy wanting the old casings back....

b22b

 

That CAD drawing should be useful, did you measure the upper and lower mounting surface diameter?


If you are measuring a brand new OEM mount 110mm may be too tall for a solid poly mount. I bet the OEM ones settle/compress after a day or two.