These are the SHORT versions of the NC Mount which lowers the engine 1/4 inch so the larger 2.5 engine will sit correctly. There is something to be said about getting in a car that feels firm. It gives you a sense of confidence and quality in the car you're driving. These mounts drastically improve on Mazda's original equipment. The re-designed mount literally takes a whole new direction when dealing with torque. If you're the weekend Auto X type, expect more predictable shifting. If you're in a boosted configuration, expect less drivetrain slop or that feeling of wheel hop that occurs when your factory mounts allow your drivetrain to flex and "bounce" back into place under heavy loads.
All the way around this is one of the more noticeable improvements to the way your beloved roadster feels. We've personally destroyed 3 sets of OE and Mazda Speed mounts on our NB Miata and as usual, we're now offering our customers something that we trust.
When choosing the bushing duro keep in mind the limited amount of material that's actually being used with this design. 70D will feel firm, in fact we really recommend this for EVERY application unless you're looking for someting with extremely little to no vibration isolation.