Earthad58

Okay so I've been told a million things and I'm looking for real world experience, I'm swapping my factory 350 th350 69 cutlass car with a 455, I will be using 350 motor mounts and I have a brand new set of hooker headers already coated for my 350 and I'm rounding up all my swap parts so when engine comes back from machine shop I can swap it in smoothely. I spoke with a gentleman whose has "built many of these cars" and he swears up and down that the small block headers will fit on the bbo, understanding I'd have to modify the exhaust to fit, before I drop $ on headers can someone verify this? Also has anyone used patriot headers they make for the 455 in this cutlass?

svnt442

Nope. They will hit all over the place and won't even bolt to the head.

I have no experience with them so I'm no help there.

joe_padavano

SBO headers WILL bolt to the head, but they will not clear the rest of the motor or chassis. The BBO is about 1" taller than the SBO. That means that the exhaust ports are in a different place. Even the right headers will typically fit like crap. The wrong ones are a non-starter.

FYI, the "350 mounts" are irrelevant. The crank centerline is in exactly the same place either way. That has no affect on header fitment. In fact, in 1968, the "350 mounts" were the ONLY mounts for SBO and BBO.

Earthad58

SO what is the difference between big block olds motor mounts and small block? They are different part numbers

joe_padavano

For nearly every model year that BBOs and SBOs were produced simultaneously, the motor mounts were EXACTLY the same part number (within a given year). The only time they were different was model years 1969-1972, and ONLY for the A-body cars. The difference had nothing to do with the block, it was a redesign for strength. The block centerline remained in the same place - the mounts were changed where they bolt to the frame pads and thus the frame pads changed. Starting in 1973, this stronger mount was used for ALL Olds motors, not just the BBOs. This is why, despite what people say, it is not correct to call them BBO and SBO mounts.

Read this thread.

matt69olds

I'm using hooker 1 7/8 headers on my 455 69 Cutlass, they fit great. I had already moved the brake distribution valve on top of the framerail when I rebuilt the brake system. Other than that minor issue they fit great.

Earthad58

Did you have to move the brake distribution valve to fit the 455? Also did you have to change brake booster? I'm still not sure what to do for valve covers, I have roller rockers with poly locks and my car is a ac car

joe_padavano

The HVAC box and booster clearance problems are the result of your valvetrain and have nothing to do with the 455 swap - 68/69 cars came with BBOs from the factory and cleared just fine. Unfortunately, you are on your own with the tall valvetrain. Lose the HVAC box (Vintage Air under the dash if you need to have A/C) and convert to a hydroboost or manual brakes.

oldcutlass

If you use the short polylocks you can probably get away with stock valve covers. Use the thicker valve cover gaskets.

Earthad58

I would rather modify my factory ac box then delete it or swap in another system, can't be that hard to cut both and fiberglass a small patch, the booster I've heard I can't just buy the 7" replacement dual diaphragm booster and that should work in just wondering if anyone else has had to do this, trying to order all the parts I need before I try and stuff the motor in, thanks

Fun71

This is what I did on my engine.