[Skip Fix]

So from the discussion it sounds like one set of mounts moves the motor a little more forward? If so does that affect trans mount location?

[Scarebird]

I always frowned at mounting at the pan rail. The extra bolt and relocation of the 455 mount helps but I would think the biggest issue for stock vehicles would be shock loading; ie. hitting large potholes, etc.

This is GM's LT architecture (2014-present). Evidently the General's march toward progress is webbed mounting in line with the bulkheads and centered on the motor. Note these are deep skirt motors; the row of 5 bolts above the pan/block line are cross bolts for the main caps.

['ol Pinion head]

Originally Posted by Skip Fix

So from the discussion it sounds like one set of mounts moves the motor a little more forward? If so does that affect trans mount location?

The 455 frame mtg brackets are moved fwd & line up with the further fwd mtg of the 455 motor mounts. No difference in where the engine is fore/aft in the chassis. Buick did a very similar thing with the slightly fwd mounted cast iron engine to frame pads their 70-72 GS 455 models.

[Skip Fix]

Roger I guess I will go look at a block used to my second gens using the same bolt holes on a 455 and a 400!
I guess the forward mount hols vs back ones are just the difference

[Sirrotica]

To further demonstrate the change, the first picture has the early 2 bolt mount. Notice it straddles he #3, or center main bulkhead.



The second picture shows a 5 bolt dual pattern. The first and third holes are used in the 455 later style mount, along with the raised hole. This puts stress on the #2, and #3 main web bulkheads. It took me awhile to see the thoughts of the engineers, but when you see he blocks from this angle, the engineering change is pretty obvious. You also see the #2, and #4 holes are the early design in contrast. The extra raised stiffening ribs near the late mounts are also very evident.

[rolling money pits]

Originally Posted by Schurkey

"I" would buy some Chevy (Camaro, so parts availability is guaranteed?) clamshell-style mounts that could be attached to the frame, and then fabricate a pair of brackets that bolt to the engine--potentially using modified steel brackets from a stock-style mount with the ruined stock rubber removed--so the bolt holes to the engine are already in place and correct. The clamshell mounts are enormously safer/stronger than the bonded-rubber style, readily available in OEM rubber, aftermarket junk rubber, or aftermarket Polyurethane (provided you choose the application wisely.)

The advantage to the clamshell style mounts being that even if the rubber totally disintegrates, the engine stays more-or-less in place under torque load and G-forces. It may clang as it rises up, and bang when it drops again...but safety is not sacrificed. (You'd never let your engine mounts get THAT bad.)

Anyone who can put a Mustang II crossmember into an A-body should be able to clamshell-mount the thing half asleep.

I’d love to do that as well, the clamshell route. Looked into that, and it’s a bit wonky from what I could figure out. Different bodies got different block mounts, etc.

I just saw this….

https://butlerperformance.com/i-2445...ml%3Fq%3DMount

Very little info on Butler’s or Warpath’s site on it, on the surface it appears to do exactly what you/me are looking for?

[Dragncar]

I am still using the 455 big car style motor mounts (Mighty Mounts) on my 73 400 High Port stroker build. Only I have the elephant ears and a mid plate as part of it.
The motor mounts are for location and fore and aft movement. With the elephant ears you can pull the trans and the engine does not drop in the rear when mid plate is removed.
Thing was with the OEM 455 mounts only, the engine rocked less then with the Mighty Mounts. Not really a upgrade.

[Schurkey]

Originally Posted by rolling money pits

https://butlerperformance.com/i-2445...ml%3Fq%3DMount

Very little info on Butler’s or Warpath’s site on it, on the surface it appears to do exactly what you/me are looking for?

That's a lot of money for two ten-dollar aftermarket clamshells, and some steel engine brackets.

OTOH, it's a bolt-in solution that requires no engineering, fabricating, or welding.

[Scarebird]

Originally Posted by Schurkey

That's a lot of money for two ten-dollar aftermarket clamshells, and some steel engine brackets.

OTOH, it's a bolt-in solution that requires no engineering, fabricating, or welding.

Not sure about the no fabrication part. IIRC the frame mounts will need holes drilled to match the newer clamshells.

[Sirrotica]

No matter what type of stock motor mounts you use, in a hard usage scenario they are going to first stretch, then loose the bond from the steel and then tear, and fail.

I learned years ago that without a hard restraint to limit the engine movement 500 lb ft of torque is going to destroy the rubber no matter who makes the mount. Years ago I devised a turnbuckle restraint that is infinitely adjustable to tune the amount of movement it allows before it puts a hard stop to save the rubber in the mounts. I usually leave 1/8" of movement before the turnbuckle stops the engine then it applies the torque stress to the upper portion of the engine. Having a small bit of adjustable movement, still allows the rubber to soak up vibrations, as it was engineered to do.

I've never used any steel mounts in any Pontiac, race car or street car. You're stressing the thin area of the block just above the oil pan rail, way more than the engineers ever designed it for originally.

I attach the 3/8" turnbuckle to the frame rail, and attach the other end to the front of the cylinder head. The reason I want the limiting device on the front of the head is the water crossover will transfer the torque stress from the attachment point, through the water crossover, then to the right cylinder head.

This takes the bulk of the torque stress from the pan rail area and the main bulkheads. I've seen quite a few grenaded Pontiac engines in race cars that the #3 main web is cracked up to the cam bearings, some caught the cracking before the engine scattered, some didn't. The common denominator was relying on the stock mounts to restrain the engine, sometimes steel mounts, sometimes basic parts store mounts.

My advice is if your going to hammer the car hard, don't rely on the either type (2 hole, or 3 hole mount) to limit the engine movement of a car that is raced or just abused on the street. Add slicks to the combination, and everything gets multiplied. Street cars with 6-800 HP aren't uncommon any longer.

Of course you can go the motor plate route too, and just disregard the OEM mounts.

Tat's my take on the mounts, YMMV........

[tekuhn]

I stopped getting notifications on this thread and was not aware of the new responses. There is good information in here from everyone - thank you.

I received the Ames 400 mounts last week and they are very nicely made. I do understand the advantage of a clamshell which will positively prevent an engine from becoming unrestrained, but the factory design does include the large interlocking tab that should prevent total separation. For my application - ~425hp on street 235 tires - I will not be stressing things too much. I feel like I can also keep the factory mount and frame attachment tucked as close as possible to the engine which is important since I will be dealing with exhaust, steering shaft, and mechanical clutch linkage all on the driver's side and I need as much space as possible.