For those of us old Harley owners, there is a difference in the Harleys with the solid mounted engines and the rubber mounted engines.
I always preferred the solid mounted engines over the rubber.

 

I believe the calculatation of lifting force on the left motor mount from the torque the engine develops is a bit more ( significantly more) than 125#. If it were only 125# you would barely need another mount to resist the lifting force at all. Just the weight of the engine would nearly be sufficient. The rubber would never tear.
The acceleration of that tab Into the stop once the rubber tears will add significantly to the shock force of the equation.
I tore stock rubber mounts before I even rebuilt the engine just with minor HP improvements. The chinesium ones these days are likely junk. Or you could try to find good ones? Maybe?

There literally is no down side to a metal left motor mount.

 

400# engine TQ - 275# dead weight = 125# upward force on motor mount.
Worse with a Big Block. Maybe up to a 275# upward force.
I agree the typical anchor / parts store ones are garbage.
The CC ones are different, thicker metal, and may? have stronger rubber
The old (long gone) Lakewood ones had stiffer / tougher rubber. They usually did even stand up to street BBs.

The 73+ up C3s have rubber body mounts. I agree there may be no downside to a metal motor mount in that application.
Some of the cars have aluminum body mounts. Vibrations are much more of a problem on these cars.
Metal motor mounts with aluminum body mounts leave nothing to dampen out any drivetrain vibrations.

Realize the driveshaft always has a speed oscillation / vibration due to the u-joints.
IF the 2 u-joint angles are exactly matched, and IF the oscillations cancel each other out, you may not feel it.
A little rubber in the system, somewhere, helps ensure these vibrations do not reach the driver.

I have a much bigger problem with my combo. 550# TQ BB, TKX so it needs driveline angle alterations, and aluminum body mounts.
It basically needs a solid left motor mount to be safe.
I am contemplating short C2 rubber body mounts, which should help with vibrations. (The C3 ones would lift the body)
Is it enough?
I don't know.
I will build a custom left rubber CC engine mount, and also have a solid one on standby.
I am not even sure which one I will try first.
Maybe I will have to try both.
And then just keep an "eye" on it.

I'll keep you informed after the car is done and a couple of drag strip launches! LOL

 

Hey Leigh,
There was a recent thread where the member did a body off restoration.
He swapped the 71 aluminum body mounts for the C2 rubber mounts and ended up with clearance issues between the floor and transmission crossmember.
He swapped back to the oem aluminum and had the clearance he needed.
Also keep in mind that if you lower the body with the C2 mounts it will also decrease the air cleaner to hood clearance by the amount you lower the body to the frame.

 

I saw that one.
The removeable crossmember brackets were touching the floor.
Not sure why. If he used David's, and I think he did, they shouldn't.
He switched to the taller 73+ up rubber mounts, and gained an extra 1/2"
And he reported vibrations were much reduced.

The C2 rubber ones and the 68-72 aluminum ones are the same height, like a 1/2"
The 73 rubber mounts are taller, like an inch tall.
I did some measuring on that a while back.

If used on my 72, they would raise everything 1/2".
Doesn't sound bad until you realize the fan won't fit into the shroud, etc. etc.
A lot of those 73 parts are different.
I used David's removeable crossmember brackets as well on my frame.
They better not hit my floor.
One more thing to check when I get there!

 

You need to get motivated back out in the garage and make some progress on yours.
I had to force myself back to work on mine.

 

Ain't that the truth!

I keep squeezing other home projects in front of it.

 

Same here.

 

You's guys need to get your priorities straight!