Best motor mounts for the money, C-3 77 with a 390hp 350 going in.

Suggestions are appreciated.

 

Solid steel. Rubber on the trans mount

 

Mike,

Moroso makes a fine pair. Summit sells the fine pair. (Around $50)

Then order all new Grade 8 bolts and a bottle of Loctite Blue.

 

Corvette Central's C3 mounts are exact GM and fit perfectly on my '72's frame horns vs. the 2 sets of aftermarket Anchor brand that I tried which were very sloppy.

 

A few years ago, I was chasing a driveline vibration issue. I installed new Anchor mounts, as my original mounts were about 50 years old.
It was not the mounts.

Left side Anchor mount only lasted about a year, rubber separated from the metal. Installed another Anchor mount, it only lasted a year or so, same problem.
I reported to Anchor, stated, not looking for compensation, no response from Anchor.

Then installed the 50 year old original factory mount, it's been good for the past few years, no problems.

The vibration was the harmonic balancer. (Damper)

 

You may likely feel some vibration with the solid mounts.
Rubber ones should be smoother.
Many aftermarket ones are either thin metal or do not fit a C3 well.
Corvette Central has some made especially for C3s.
Those are the ones I would use.

 

I would never use solid motor mounts. By using a solid motor mounts you now made the engine a structural member of the frame. Anyway that's my 2 cents. I use Anchor motor mounts from RockAuto. They have a tab that will restrict the stretch of the rubber under acceleration, good fitment, and they seem to last.

 

You better walk around in the pits, at the track.
Half the cars there have engines stabilized to the frame for structural integrity.

I learned back in the 70s not to trust Chevy rubber mounts in cars made in the 70s.
Good grief, those things snap like twigs.

I have Moroso solids now. Very-very little vibration in the wheel.
It's an old sportscar. Not a modern luxury car.

 

A engine plate is not the same as solid motor mounts and those tracks cars are track cars. I believe in rubber for suspension and motor mounts for a street car. I tried urethane rear suspension components in my car early on. I couldn't stand it and switch it back to rubber after a month.

 

You just may believe that. Doesn't mean we all do.

 

I use a solid motor mount on the left side and rubber on the right side, poly transmission mount. No vibrations to report. 400+ HP.

 

I installed Moroso solid motor mounts for my 73 big block.
Call and talk with Moroso’s customer service technicians.
They manufacture solid mounts in three different heights, so make sure you get the correct ones for your engine block.
Just ordering a generic set for a sbc from Summit or other vendor may cause you issues down the road.
Just make sure you run a good quality rubber (preferred) or good quality Energy Suspension poly transmission mount and do not run a solid transmission mount with solid motor mounts.

 

Well, not exactly.

Rubber front / rubber tranny (stock)
Steel front / rubber on trans (very common w/ high torque)
Steel front / steel on trans (common with gobs of torque, racing)

But never! Rubber front / steel trans. Engine moves but tranny does not.
Something has to give. It's usually the bellhousing that cracks.

And in some rare events, the tailshaft housing cracks at the mount.

 

Try Rock Auto

 

Agreed, but the OP didn’t mention anything about building a total race car so I kept it more simple.

 

The Corvette Central mounts will be ideal for a 390HP motor.

 

All rubber mounts would be fine IF you could depend on the left one not ripping apart causing the engine to rise during acceleration and causing problems. Reason WHY I use solid on the left side. More HP than stock, greater chance of that happening.

 

Very true!
These have a safety catch that only permits 1/8" of upward movement.

 

Although that is true, it's still broken once it rips. And given enough torque that tab may fail.

 

Also true.
I would estimate a SBC weighs about 450-550#, depending on how many aluminum parts it has.
Half of that rests on the left motor mount, or 275#.
With a 400# of TQ that means a lifting force of 125# on that mount. But only at WOT.
Cruising down the highway, using only 50#TQ, there is plenty of downward engine weight on that mount.
For the OPs SBC, unless he is racing, I would still recommend the rubber mounts.

FWIW my 80 era Lakewood? Muscle Mounts (rubber) lasted thru 27 years of racing, with zero issues.
I do not know the quality of the current Corvette Central Mounts.
They look correct, but I do not know if they are made for HD racing use like the Lakewoods definately were.
But they are no longer available.

OTOH the rubber helps to prevent minor vibrations from getting transferred to the driver.
That "drone-ing" or "tingling" sensation can get very tiresome on a trip. BTDT
For short rides it is part of the vintage experience LOL.

I am more inclined to keep the Central rubber mounts, to help with cruising vibrations, because I am planning a coast to coast trip, or at least the Power Tour.

OTOH as you pointed out, I do not trust the strength of that tab, on the left mount, with a 550#TQ BBC, and I have already planned to improve those mounts, by reinforcing the tab, to handle BBC force, and reduce the clearance gap, to like ~.100" to limit upward movement and reduce tearing of the rubber. It is too large right now, like 1/4" and the mount will tear before there is any contact. Almost no clearance is required, .060" would likely be enough. I will even do some measuring when I modify mine.
My reinforced design will go "solid" or metal-to-metal after ~.100" lift, and be robust enough not to bend.

If anyone has ever driven a race car, with a tingling / buzzing steering wheel, and buzzing dash parts, that is what can happen when you eliminate all rubber from the car.

My Pro Solo Z28 had no rubber anywhere, except for the tires, and the motor mounts. Buzzing and vibrations were not a problem. But the suspension springs and shocks were so stiff that it was punishing and exhausting to drive for an hour.
If I held a cup of coffee, it would just sit there and splash, all the way to the roof!

I do want this car to handle nearly as well, but be a better cruiser. It will definately be faster.
Making it smooth is actually my biggest challenge.
I can't make it so rowdy that my wife won't ride with me! LOL