Hello All

The 403 Olds in my Trans Am has breathed its last,I was considering a small Block Chevy as a replacement, but a W30 455 in good condition is available.

I was wondering if you can tell me if the 455 will fit the same motor mounts currently in the car. My built up TH350 has a BOP housing so it will take the block. Is this a bolt in or do I need to change a bunch of brackets and motor mounts to make this work?

Thanks in advance for your opinions.

 

I would assume it would considering the 403 was modeled in a sense after the 455 but then again the 403 is a small block I believe. Good question nonetheless someone more experienced will help better than I can

 

Yes, the only external difference between the 455 and the 403 is the deck height. Transfer the metal motor mount brackets from your 403 to the 455 and the BBO bolts directly to your trans and frame mount.

The accessory brackets are a little more of a problem, since they were not designed to fit the taller deck height of the 455. These brackets are unique to the F-body, so conventional Olds accessory brackets won't work. You'll have to bolt them up and see how they work. If the brackets ONLY bolt to the block or ONLY bolt to the head, they will fit the 455 with no problems. If any brackets span between the block and a head (or the intake) you'll need to cut and weld to accommodate the taller deck height. Any head-mounted accessories will require a longer fan belt due to the taller deck height. Also, either use the water pump for a 403 or at least be sure that the pump on the 455 is the same length as the one on the 403. There are three Olds water pump lengths.

Here's the A/C bracket. Note that it only bolts to the head, so no problem there. Also note the special tube and fittings that relocate the oil pressure sender due to the alternator being in the way on the F-body applications.

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Here's the oil pressure sender tube:

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Here are the alternator and PS pump brackets. Note that all but one of the bolts attach to the head. The one that goes to the block will require an extension to be welded on. Yeah, that's got to be the crustiest engine I've ever seen... Don't worry, it isn't mine.

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