Solid vs Poly Motor Mounts

[SicMonte]

Calling all my pro-touring friends, car builders, shop owners, road racers and autox'ers:

Discuss the pros and cons of running solid motor mounts in a pro-touring car....especially with a sbc and a t56. Please give personal and detailed experiences. Thanks!!

[Ben@SpeedTech]

I can't remember what cam you have but if it's fairly lumpy, well, solid motor mounts with a gnarly cam will rattle your fillings loose, lol! I found running a regular mount with a short stretch of chain connecting the driver's side of the block to the frame worked really well. Not much flex in the drivetrain but less vibration from the motor. That's the extent of my experience.

[astroracer]

Run a solid on the drivers side and a rubber on the passenger side.

[vette427-sbc]

The whole solid motor mounts vibrating the hell out of the car is not true for a well balanced motor... I run solid motor mounts on my cars because it adds a noticeable amount of rigidity to the chassis. Both are daily drivers and everyone is surprised when we tell them the car has solid motor mounts. Both cars are also SBC/T56 cars with a rubber mount on one and a poly mount on the other. Dont like the poly mount so that will be going back to rubber.

[astroracer]

The whole solid motor mounts vibrating the hell out of the car is not true for a well balanced motor... I run solid motor mounts on my cars because it adds a noticeable amount of rigidity to the chassis. Both are daily drivers and everyone is surprised when we tell them the car has solid motor mounts. Both cars are also SBC/T56 cars with a rubber mount on one and a poly mount on the other. Dont like the poly mount so that will be going back to rubber.

What type of cam are you running? Sorry but a well balanced motor has nothing to do with it...It all comes down to idle quality and, if the engine has a lot of cam and is lumpy down low, it will generate a lot of harshness through solid mounts.
Mark

[vette427-sbc]

Solid roller with 236-242 duration ... Not a super wild cam but certainly not an RV or truck cam with no lop to it. It is not even close to generating any noticeable vibrations, noise or harshness. Just talking from my experiences. I wouldnt hesitate to put solid mounts on another car. Of course there are extremes to every situation and yes a car with a very large cam where the idle speed varies by hundreds of RPM will vibrate a car. I shouldnt have worded my response as such a blanket statement for all motors.

[SS PUNISHER]

I've ran all three and solid mounts felt better to me than poly. The poly mounts seemed to vibrate alot whereas the solid mounts would be more of a shake. Don't know if that makes any sense at all lol.
For what it's worth, this was all in the same vehicle, s10 with a bone stock tbi 350

[astroracer]

Some consideration has to be given to the body mounts also. Stock rubber mounts will help dampen the input where as solid body mounts will transmit more vibration.
Using solid engine mounts in a vehicle with rubber mounts will not feel that bad.
Mark

[SicMonte]

I've heard that solid motor mounts put added stress on the drivetrain....any ideas on that?

Also heard that running a stock bellhousing is a bad idea when running solid motor mounts?

[bdiamond]

I have always heard solid mounts on the engine or transmission but not both. The twist would break a bellhousing. Sounded logical so I've never tried to prove it wrong....

[Randy67]

I have sold motor mounts, rubber transmission mount, solid body mounts and a full cage on my 81 CP autox car. Vibration is not bad at all, much less than I was expecting. The cam is a 266 @ 0.050" duration so it isn't mild by any means. I notice more noise from the rear suspension heim joints than the engine/trans. Of course my car isn't the quietest car inside by any means, so that could mask some of it.

[camrat68]

I've had rubber, solid and now poly mounts in my 68.
Solid mounts on the engine and trans led to a cracked bellhousing on a Saginaw 4-speed behind a mild 454BBC.
Solid mounts with a rubber trans mount worked fine but I ran into a vibration issue at WOT due to the breakdown of the rubber mount due to an oil leak. I switched to a poly trans mount and lost the vibration.
I switched to poly mounts on everything now.
I'm currently running a fairly mild 597hp 502 that's balanced to 8000rpm that will make the whole car dance at idle when parked.
I had solid mounts in my 68 Camaro for a while until the constant vibration convinced me to change them out for poly mounts. The stock rubber mounts were prone to separating on the older cars because of stress and lack of resistance to underhood chemicals like gas and oil that breaks down rubber making a chain or cable neccesary and solid mounts as a better choice. When the poly mounts came out, they had an interlocking design that would prevent separation even if the poly material failed which was less likely due to the poly material being more resistant to petrolium based chemicals.
In your case though, you should have the newer clamshell mount that sandwiches the rubber mount between the frame and a top steel shell as the frame side mount. My Caprice uses the same thing as well as a solid stamped steel engine side mount. What does your Monte use?

As you know, a manual trans will transmit more power to the ground faster than a slushbox making some give even more neccesary.

Jim

[SicMonte]

I've had rubber, solid and now poly mounts in my 68.
Solid mounts on the engine and trans led to a cracked bellhousing on a Saginaw 4-speed behind a mild 454BBC.
Solid mounts with a rubber trans mount worked fine but I ran into a vibration issue at WOT due to the breakdown of the rubber mount due to an oil leak. I switched to a poly trans mount and lost the vibration.
I switched to poly mounts on everything now.
I'm currently running a fairly mild 597hp 502 that's balanced to 8000rpm that will make the whole car dance at idle when parked.
I had solid mounts in my 68 Camaro for a while until the constant vibration convinced me to change them out for poly mounts. The stock rubber mounts were prone to separating on the older cars because of stress and lack of resistance to underhood chemicals like gas and oil that breaks down rubber making a chain or cable neccesary and solid mounts as a better choice. When the poly mounts came out, they had an interlocking design that would prevent separation even if the poly material failed which was less likely due to the poly material being more resistant to petrolium based chemicals.
In your case though, you should have the newer clamshell mount that sandwiches the rubber mount between the frame and a top steel shell as the frame side mount. My Caprice uses the same thing as well as a solid stamped steel engine side mount. What does your Monte use?

As you know, a manual trans will transmit more power to the ground faster than a slushbox making some give even more neccesary.

Jim

My monte has the clamshell style newer motor mounts.

I have poly motor mounts and trans mount.

My most recent "sponsor" is coming out with a new solid motor mount kit and I wanted to run them so that's why I put this thread up....to see what other peoples experiances were.

Im hearing stuff all over the board...good...bad...broken bellhousings...etc.

[TheJDMan]

I have run both solid and poly mounts and to tell the truth I could not tell much difference in vibration or noise levels. I'm going to be dropping the engine back in Dust Off in the next couple of weeks and at this point I'm undecided which set of mounts I will use. I don't think a cracked bell housing would be an issue if using an SFI rated unit.

[MonzaRacer]

Always run non solid mount on trans if engine has solids unless you want cracks in your bellhousing.
when I built my 70 Monte, I built solid motor mounts. As long as solid mounts are TIGHT, your engine is then trying to shake WHOLE frame. Not engine.
Several buddies use poly, no issues, I like solids, had motor plates in few cars, no vibration issues.
Always used solid rubber style trans mounts, never had a failure or broken parts.

[icemanrd19]

what about poly vs rubber t56 mounts? I have a slight vibration which i feel is in the trans and I'm wondering if its because i have poly mounts everywhere

[cluxford]

I have a tall deck BBC and TH400 so not same as what you have, but I run solid motor mounts, solid body mounts and rubber trans mount. I get very very little vibration. I get more vibration and noise from the Heim joints on the 4 link

[TheJDMan]

I can't remember what cam you have but if it's fairly lumpy, well, solid motor mounts with a gnarly cam will rattle your fillings loose, lol! I found running a regular mount with a short stretch of chain connecting the driver's side of the block to the frame worked really well. Not much flex in the drivetrain but less vibration from the motor. That's the extent of my experience.

This fix made me smile. This is what we did back in the late 60's and early 70's to tie an engine down because there was no such thing as solid or poly mounts. Only later in the 70's did Moroso start selling the first solid mounts.

[rich_fbodySS]

I've used the solid steel mounts in all my cars since I was a teenager (early 1980's) and have never had a big vibration problem.
More noticeable harshness comes from solid body mounts in my opinion...

I've always had motors that made less than 500HP (flywheel) and my friend that builds motors cautions against higher horsepower motors (over 500) using the solid mounts as he says it sometimes distorts the cylinder roundness near the motor mount holes...he says over 500HP s/b using motor plates (either front or both front/rear) for mounting to frame/subframe.

-Rich