Well this explains a lot.

 

I shelved my Blackbird big bushing mounts over a year ago for Mazdacomps. I still think that "downgrade" was the best thing I've ever done to my car in terms of general enjoyment. This past track day I sat in a car with some other brand of poly mounts (EDIT: They were Innovative Motorsports models with the tapered bushing) and was amazed at how much more civil they were, definitely something I could live with. I've been trying to figure out what could be different between the brands of poly mount, and this seems like a really good contender.

In for results. These Mazdacomps won't last forever, and I'll dust off the Blackbirds at that time if this can make the difference.

 

For what its worth, I have a prototype set of the softer durometer street mounts on my mostly stock 1.6 and it went from intolerable (with the old street durometer) to totally worth it. So hold tight for the softer bushings to come in if you're bothered by the NVH. And maybe while you're waiting, tighten some screws on the things that are rattling the worst. That can help...

 

Pretty cool that the lead engineer of the ND Miata just swings by for a casual chat about aftermarket parts. I love this place.

Anyways, building on the bushing fit, I think it could be contributing to why people have such wildly different opinions of these things, beyond different tolerances for NVH. If shaving a half a millimeter off the bushing can be noticed, imagine what car to car variations in engine location will do. One guy could have a car that sits right in the middle of these mounts, while others may have an engine located just a few mm fore or aft and gets a very preloaded bushing that transmits vibrations as if it was a solid mount. My mounts have the bushings on both sides seated all the way to the rear, so it's probably fighting the PPF/diff mounts to pull the engine forward. I measure a 2mm difference in the gap between the front and rear of the mounts, on both sides, after being off the car for over a year.

 

I have been holding tight for this, still doesn't look like they're an option yet.


Adding the shims to the crush tube didn't offer a step improvement, though perhaps it needed more shimming. I don't really see how this style of mount can effectively work in the fore/aft direction without having the thrust faces bypass the isolation unless it's undersized and just uses the diff mounts to locate the powertrain longitudinally.

I'm getting tempted to pull the exhaust side one and try something like the supermiata hybrid style then try and come up with some kind of torque reactor mount as far from the crank axis as I can. I do need to sort this as it's the only part that makes the vehicle unpleasant on the road. Even the #800 front springs are pretty much unnoticeable vs the mounts.