I just ordered the RR-Racing front motor mount inserts a couple of weeks ago. They were inexpensive and came in a reasonable amount of time. I just spent about 30 minutes tonight putting them in the stock mount.
Bottom line - this is a no-brainer. I could hold the stock mount in one hand and move the inner metal sleeve about 1/2" each way by hand - that's how soft it is.
The inserts are cake to install. Loosen the nut for the bolt through the bushing first (17mm). Loosen the two nuts holding the mount to the subframe on the very bottom of the car (17mm again). Take everything loose remembering or marking front-to-back orientation. Pull it out of the car, I had to clip one of the rubber nubs sticking out of my stock bushing to be even with the other one and fit in the inserts. The inserts have mating voids to the bushing nubs - two on one side and one on the other - so it's easy to get orientation right. Push the inserts in (I didn't have ANY trouble with this - some others have used grease or WD) and put it all back together. You can see pictures of the mount and inserts in various states of assembly
here. Sorry, I didn't feel like taking my rather expensive digital slr out under the car, so I didn't get pics of the mount in the car. Plus, it's easy enough to find.
Impressions:
1. Vibration: So far I've hardly noticed any difference from before. I ran in a lot of different conditions including idle with A/C. This is NOT a problem, although wintertime will be a better test.
2. Wheel Hop: Anybody that says this will help with wheel hop is on crack. Wheel hop is a function of the suspension geometry, masses, and spring weights, maybe body stiffness. It shows up when a tire spins, but is a result of the things I've just mentioned. I designed racing suspensions in college and have worked as an automotive suspension design engineer for the last seven years (2 years in Germany). This insert does not / can not do anything for wheel hop. The remedy for wheel hop is to put in a limited slip differential so the wheel doesn't spin in the first place. Otherwise you'll have to look at the spring/mass/damper equations for this suspension and figure out how to critically damp the wheel by changing the shocks and springs.
3. Shifting: Here's the huge improvement over stock. Everybody that drives a P5 knows how badly the engine rocks during agressive shifts. First there's the mush you get trying to launch in first, then the pulsing when you engage your next gears. These RR Racing inserts don't eliminate that, but I'd say they're an 85% improvement. Heel-toe downshifts are clean now, and the 6000RPM shift from 1st to 2nd doesn't make you feel like your engine might drop out of the car.
4. Surging at low speeds in 1st gear: Maybe improved a little, but not solved. There's something going on with engine calibration here. When you're off the gas idling in gear and you press the gas pedal, the engine first dies and then picks up acceleration. I'm sure it's a "lesser of two evils" thing where Mazda had to make emissions or facilitate cold weather starts or something. No help here from the inserts.
So the way I see it, this thing is cheap, easy to install, I see no downsides, and you get much improved shifting. Everybody on this forum should have these installed (except for those with more agressive mounts like AWR).
LOL.
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