Engine and gearbox mounts are often overlooked, whether for maintenance or for performance. Yes, performance. Although the foremost job of drivetrain mounts is to dampen the noise and vibration from the mechanicals of the car to the cabin, it can also affect power delivery, shifting, and even handling.
These mounts are normally simple pieces of engineering, much like suspension bushings. They usually consist of a rubber material to dampen the vibrations, a metal support structure to encase the rubber, and sometimes have clever tricks like hydraulic oil or magnetorheological fluid to actively change the stiffness of the mount, like with Porsche’s Active Drivetrain Mount (PADM). A lot of modern cars deploy a passive fluid volume to more effectively tune out vibration while having stiffness for performance.
The mounts don’t just locate the drivetrain in the car, they also absorb the torque and lash from it. For example, shifting gears or transitioning to deceleration causes a whip in the drivetrain that needs to be attenuated without damaging the gearbox, driveshaft, or differential and the mounts make the experience smooth for occupants. Race cars solid-mount everything because passenger comfort doesn’t matter and race cars get regular major servicing.
Softer engine mounts famously cause axle hop or wheel hop. Basically, when the driven wheels start breaking traction, the drivetrain winds and violently unwinds at a high frequency as the tires catch grip and release. This causes it to generate serious energy and destroys axles, joints, and mounts. It’s usually why people break things by launching their Mustangs or similar 1320-friendly cars. Stiffer rubber, polyurethane, or even solid mounts can solve the axle hop issue at a refinement cost. For my purposes, a stiffer rubber mount helps prevent hop and provides crisper power shifting.
But the most interesting thing about engine mounts is the fact that they can improve handling, specifically turn-in and directional changes. This is because these mounts also have to support the weight of the heaviest parts of the car while cornering and jostling around. Next time you have a friend in the car, have them jostle the car as hard as they can in the passenger seat. You will feel the car get a little bit upset, and the average American weighs 178 lbs. An engine and gearbox can easily weigh 600 pounds, so imagine the effect that can have when it shifts around thanks to soft or worn mounts.
Having stiffer mounts can control the secondary motion of the drivetrain and drastically improve cornering in situations that require response and especially over mid-corner bumps. Truthfully, this is much more effective when replacing worn or blown mounts than it is trying to upgrade new factory mounts, but the upgrade is still interesting. I did it to my 2010 VW GTI with 034 Motorsport mounts that were made of slightly stiffer rubber than factory.
For an enthusiast, the stiffer mounts also allow some extra vestiges of vibration into the cabin that are sorely missed in modern cars. It can become too much with overly stiff mounts, but if the mounts are chosen with some consideration, a great balance can be achieved.
On my front-wheel-drive GTI, the transverse engine layout makes the engine and gearbox mounts do practically the same job. On something rear-driven like my old BMW 330i ZHP, the engine, gearbox, and differential mounts could do slightly different jobs. Either way, all mounts should be matched to each other. Having a single polyurethane mount mixed with stock rubber can cause vibration and strange noises.
Rear-wheel-drive cars get a little bit more interesting than my GTI, allowing different symphonies to enter the cabin. Stiffer gearbox and differential mounts allow gear whine and gearbox noise to sing a little bit, which adds a pleasant race car sort of gear whine to the experience of a car. Engine mounts can easily make an engine louder in the cabin while introducing quite a bit more vibration. Simply put, stiff engine mounts make the engine more present in the cabin.
Engine mounts are an interesting mod that can end up making a car worse, so keeping it stock isn’t the worst thing. But it is one of the many small parts of a car that can be tuned to offer a different experience rather than more performance. It’s a wine-glass-delicate balance to achieve, but there is something to be found, even if it’s miniscule.