Odd question about replacing motor mounts...

[ahkenaden]

So, in the almost 15 years I've had this car, with all of the various and massive amounts of Google-Fu that I have utilized, I have never seen anyone speak on why you would want to replace motor mounts with poly alternatives.

Any opinions as to what power level one should upgrade to poly mounts? And are there more "street-car" friendly poly's than the 80+ durometer? Should a modest power bump (given my mods...intake, zero cats, Stillen dp, 3" full exhaust, 13G's+Blitz bc, 450's, Wally255, Maf-T, Fidanza/3SX aluminium crank pulley..probably some other crap that I don't remember given the 8 years since I've regularly driven it...) necessitate such a drastic increase in NVH or would a new set of OEM mounts do the job and keep me from going insane?

I recall about 5 years back putting a SINGLE Energy Suspension poly mount in my beater 95 Sentra and good lord the increase in in-cabin vibration was spectacular. That was a tiny 1.6L, I don't want to know what a 3.0L feels like...

Thanks for any input, been out of the game for some time.

Heed

[sergechronos]

I would imagine that 3SX polys (being as they are basically poly in stock mounts) are probably as soft as you get from something readily available, you could pour your own though and use whatever hardness you like. You could MAYBE talk 3sx into pouring you something more in between, although I would advise going for a ride with somebody who has poly mounts now to see the difference. The results vary from platform to platform. My 00 Mustang used solid mounts and while there was a noticeable increase in vibrations, it was not excessive and was not noticeable when the car was moving. My girlfriend's 94 Integra, was another story, felt awful at idle and could still be felt while moving.

The benefit of poly is that it moves and flexes less than rubber, but more than solids (obviously). It's less strain on the drivetrain and less drivetrain loss due to flexing and moving, and poly tends to last longer than the factory style rubber (which I believe has a fluid filling as well to dampen vibrations.)

As said, ride with someone if you can to test and see before you make a decision on it.

[Jimvr4]

The stock setup uses rubber mounts on the front and rear roll stoppers but the driver side mount and trans mount are oil filled so they reduce vibrations. I've heard front and rear could be solids without much effect but having poly for the driver and trans mounts will increase vibration. I;ve just changed mine to poly all around so we'll see.

[ahkenaden]

The benefit of poly is that it moves and flexes less than rubber, but more than solids (obviously). It's less strain on the drivetrain and less drivetrain loss due to flexing and moving, and poly tends to last longer than the factory style rubber (which I believe has a fluid filling as well to dampen vibrations.)

As said, ride with someone if you can to test and see before you make a decision on it.

Is anyone 100% convinced about it being less strain on the drivetrain? If anything, wouldn't it be more as you are now transferring more torque (and subsequently more vibration) through the system?

And I'm in Michigan, I think there are 4 people who's cars still run and they are probably still using stock mounts

The stock setup uses rubber mounts on the front and rear roll stoppers but the driver side mount and trans mount are oil filled so they reduce vibrations. I've heard front and rear could be solids without much effect but having poly for the driver and trans mounts will increase vibration. I;ve just changed mine to poly all around so we'll see.

Hm, this would seem to make the best sense as you'd want to decrease front to rear engine flexing (a la 3SX's "jump around" video). And it would make sense that less NVH would be heard since they're mounted to the subframe which has its own set of rubber bushings. Had no idea the side mounts were oil filled. Still learning something new after all this time!

[sergechronos]

Is anyone 100% convinced about it being less strain on the drivetrain? If anything, wouldn't it be more as you are now transferring more torque (and subsequently more vibration) through the system?

And I'm in Michigan, I think there are 4 people who's cars still run and they are probably still using stock mounts

Compared to cracked/worn mounts, it is less movement. I think the type of torque and stress you are are concerned about would be torsion, however compared to worn/busted stock mounts I would imagine that it is significantly less of a concern to the engine being able to move around in all 3 axis. The vibrations and movement of the engine are still on the engine with factory mounts, even in perfect shape, the rubber and oil just reduces how much of that makes it to the engine bay.

Consider: The engine and transmission are mounted transversally. So with the rotation of the motor and torque, most of the movement is front and back when accelerating and braking. While the front and rear mounts are roll stopped, the tranny and driverside mounts (which are supporting the weight of the engine) are what are absorbing most of the vibrations from the engine running. This is why you could swap to solid mounts front and rear and not feel a bit of it, there really isn't much weight on the front or rear mounts except during the acceleration and braking as they are really just roll stoppers. Factor in the rubber bushings connecting those subframes to the actual chassis and there's just not much to feel. This is also why it is the driver and tranny mounts that are oil filled and not the front and rear, since they have to soak the vibrations up.

Polys will allow less movement forwards and back compared to the factory rubber, and the solids will obviously allow very very little front to back movement. It is this movement that I'm more worried about since any vibrations and such in the engine are just that, in the engine. Polys and solids just allow that to transfer to the chassis (and therefore the cabin). I see no worries about that.

If you have time later, you could search for a study on fluid filled mounts and how they compare. I read it a couple times before, and maybe someone else on here has it bookmarked or similar, and the conclusions were basically that mounts filled with fluids did very little compared to non-fluid filled mounts. My only concern with full solids is that with rubber carrier bearings and rubber bushings on the rear subframe and diff that the front and rear flexing differently could POTENTIALLY do damage (which would be more drivetrain stress as you pointed out) however it doesn't seem to have happened to many people running full solids. Or any people running full solids that I'm aware of actually. I would imagine that if you were to swap all the front subframe and motor mounts with solids you may run into issues, but who knows. The front subframe isn't really designed to move, and the bushings are just rubber to help dampen vibrations and bumps since this is supposed to be a GT car.

It would require a large sample size to know for sure. Although I'm sure if someone running solid or poly mounts up front had resulted in damage they would've already shown up to tell you about it.

If the vibrations are a concern for you, again you could either pour your own mounts, or just get new OEM driver and tranny mounts and replace the front and rear with poly or solids and probably have the best of both worlds.

[aaronatstate]

Is anyone 100% convinced about it being less strain on the drivetrain? If anything, wouldn't it be more as you are now transferring more torque (and subsequently more vibration) through the system?

Think of it this way. When the engine moves in the engine bay, the trans, transfer case, and drive shaft all move with it. By reducing the movement of the engine, you are most definitely putting less strain on the drivetrain.

[j2k4]

Is anyone 100% convinced about it being less strain on the drivetrain? If anything, wouldn't it be more as you are now transferring more torque (and subsequently more vibration) through the system?[\QUOTE]

Think of it this way. When the engine moves in the engine bay, the trans, transfer case, and drive shaft all move with it. By reducing the movement of the engine, you are most definitely putting less strain on the drivetrain.

A stouter leash, as it were.

I think we need to go further with this conversation and define - however anecdotally - the qualities of the different mounts in sets or combinations, by whatever consensus weighs in.

I'm interested in hearing more about an OEM/R&L - poly/F&B set-up, as this is the first time I've heard proper reasonings for it.

I might hesitate at solids, but my wife has RLS, and vibes bother her sometimes.

Since I've been trying to get her in the car for a decent road trip, this is a weighty decision for me.

I've been leaning towards new OEM all around, given I'm BPU and driving the car GT-style, but I kinda like the idea of locking the rocking.

[sergechronos]

A stouter leash, as it were.

I think we need to go further with this conversation and define - however anecdotally - the qualities of the different mounts in sets or combinations, by whatever consensus weighs in.

I'm interested in hearing more about an OEM/R&L - poly/F&B set-up, as this is the first time I've heard proper reasonings for it.

I might hesitate at solids, but my wife has RLS, and vibes bother her sometimes.

Since I've been trying to get her in the car for a decent road trip, this is a weighty decision for me.

I've been leaning towards new OEM all around, given I'm BPU and driving the car GT-style, but I kinda like the idea of locking the rocking.

Almost every transversely mounted engine is the same: Mount on either side by the shock towers and at least one more either on the front bumper side or on the cabin side to triangulate them. Mitsubishi went a step farther and put one in the front and in the back, and did fluid filled rubber mounts for the sides. The front and back are just roll stopped, you should have little (if any change) to interior vibrations from swapping the front and back. The mounts on the driver and transmission side are where all the vibrations go because as Forrest (and others) have said that is directly to the chassis and again, that is along the axis that the engine is rotating.

If you stay OEM L+R you will still have rocking for sure, can't be helped, the rubber just isn't strong enough to lock it down on it's own (not sure even solids could just due to the forces involved). But if you use solid or poly Front and Rears, you are limited the range of motion that it can move front and rear, thus reducing the wear and tear from it.

[zel-man]

The biggest difference I've noticed are during starts. Greater vibrations and a pronounced stutter out of first gear if I don't feather the clutch right.

[kywhitelightning]

If you commit to poly you might as well go solids. NVH will increase either way, solids are a lot cheaper, and poly's will wear out. I had a set of poly's in mine for 6 years and was a little disapointed that the pins were now mobile. I now have solids and there isn't too much of a difference between the two. For your modest power level stick with stock. They are worlds more comfortable. Make sure there is a good flex section in your DP and I assume you are still on the stock 3 piece DS.

A 4 cylinder will always deliver a lot more vibrations when the engine is more solidly mounted by shear nature of the time between power pulses. I4 every 90*, V6 every 60*, and V8's every 45* of crankshaft revolution.

Jeff