1971

So help me out here, had small block motor mount plates and big block motor mounts in my cutlass supreme with the 455, car had a 350 orig. So just did my rebuild on the 455 built it myself it went well. Got new BB plates and new bb motor mounts. Dropped the sucker in and OHH it doesnt fit so well?? hmm should be lower I thought with the motor mount plates. So had to pull the drivers side valve cover off to get the motor in, ok no problem. Got the motor in, went to put the valve cover back on and could not. The stupid brake booster is to close. Had to loosen the booster to get the valve cover on. So my motor is way to high now, my hood might close but not with a drop air cleaner on it???? any one delt with this before? I really don't want to pull the motor back out, and I kind of don't want to cut a hole in my hood for a scoop. And I really don't want to sell it and buy a kia sportage but I was close a few nights ago.

svnt442

If you got BB plates they are from an earlier car I believe. I think they went with one mount from 71 on, but don't quote me on that as I'm not 100% sure of the year they did that.

J-(Chicago)

You can use the car's original small block mounts and frame pads with the 455.
You should have stayed with your original equipment.

Also, the big block cars had notched valve covers to clear the booster and a/c box.
Here is a pic.

Good luck, and let us know how it turns out.

1971

Your telling me, the way it was fit better than now. I thought it would lower it since my air cleaner just touched the under hood pad. Wasted 100 bucks on plates and new mounts. Going to work on it tomorrow, I should know then how in trouble I am. Lucky that I don't have to take valve covers off that much, loosening the brake booster nuts was a huge pain.

DeltaPace77

Hmm, looks like I'm learning things a bit to late here. Funny thing is, I've done a couple 350 to 455 swaps, and direct drop in's on original mounts. The additional width wasn't much a deal, but good keeping an eye on intake manifold and air cleaner height.

svnt442

Changing the engine mounts and frame pads does not change the location of the engine in the bay at all. All it was done for was the original factory small block mounts did not come with a lock that would keep the engine from hitting the hood if the rubber tore out, but the big block mounts did do to the relocated hole for the through bolt that tied the engine and frame sides together.

1971

It shouldn't have but my motor is at least a 3/4 higher. My valve cover is about 1/2 inch from the brake booster. Small worry though I cant even get the motor to start, won't turn over.

joe_padavano

3/4" higher than the 350? That's because the 455 IS 3/4" taller than the 350. The factory mounts put the crank centerline in the same place for both motors. You can't drop the motor any more without hitting the crossmember.

1971

No I had the 455 before just rebuilt it. This might be the stock height a 455 shoul be maybe, but I have to lossen the brake booster move it towards the fender to get the valve cover on. Before with the small block plates and bb mounts the iol pan was really close to the sub frame there, now I have enough space to slide a finger under there?? I'll see when I go to put my hood on if it closes, drop air cleaner was really close before!

svnt442

You can't mix and match frame pads and engine mounts. The holes come nowhere near to lining up when you try that.

oldcutlass

You need to get BBO valve covers with the notch, as stated above. Some folks have changed to a smaller diameter power booster.

1971

Yeah these MT valve covers are tall! Smaller diameter booster might be the ticket.

svnt442

Ahhh...tall valve covers. I see the issue now. I was thinking he was using stock covers and was just a bit perplexed.