Putting some thought into putting a big block in our 68 conv. I know I have to get a big block heater core and cover, but what else should I expect or the surprises we might run across.

Plan on going with a rebuilt 350 trans and 12 bolt rear.

Ben Braun

 

A 350 is not a big block, for starters.

 

I believe he means a turbo 350 trans not a 350 engine.

You'll need all the BB brackets for whatever engine accessories you have,AC,PS etc. and you'll need a big block radiator and a trans cooler.
Oh, and of course the BB motor mounts and exhaust manifolds or headers.
Other than that it's pretty much a bolt in deal since you already know about the heater.
There could also be a clearance issue with closing your hood depending on what hood you have and what intake and carb set up you run.

 

Oh. Skimmed over a bit too quickly there, sorry. >.>

 

Thanks

Ben Braun

 

I have done this a few times.

You need the big block frame stands so the exhaust will clear the steering gear box. The motor mounts themselves will cross over.

The basic Hooker Competition headers fit nice and work well for not a lot of cash.

You can just flip the small block heater core 180 degrees and drill a couple holes in the new outlet location closer to the hood hinges.

Accessory brackets and pulleys are the biggest hurdle but you can buy everything. I would suggest going with the 69 passenger side alternator long water pump setup. It is more stable and looks a bunch better.

Only a low profile intake like the stock iron Q-Jet intake or a Torquer II will clear the stock flat hood. A Performer intake will clear the SS hood just barely with a short air filter element. I believe mine is a 2-3/4" tall K&N 14" diameter filter and I have about 1/4" of clearance. Any taller intake like a Performer RPM or Victor series will require a cowl hood to clear.

You don't have to run them but you will most likely want big block front springs. The extra 140 +/- pounds will drop the front end a bit and may cause ground clearance and exhaust system clearance problems.

Unless it is built well and upgraded the T-350 will not last long behind a big block. A T-400 with just the 34-element sprag upgrade and a TransGo shift kit is good for 800 hp with a converter that can handle the power with an off the shelf performance rebuild.

 

I've done this a few times too, and big block engine mounts wont fit the frame mounts of a small block, or vice versa. If you leave the small block frame mounts in, then you need small block motor mounts on your BBC. If you install BBC frame mounts, then your BBC needs BBC motor mounts. They are quite different in height, and size.
You'll definitely want to change the water pump to a long pump, if it's a short pump, and all pulleys at that time. I've built custom bracketry from heim ends and rod stock to accomodate short water pumps and pass. side mounting, but it's not fun.
You'' need the big radiator too, but unless you want a stock look, I'd go with aftermarket two row aluminum. The opening in the core support needs to be cut to size for the larger radiator too. It's stamped, so just follow the outline.
I didn't have to relocate the heater core, or drill new holes. It cleared fine, and was easy to install hoses, but if you ever have to remove the core with the engine in place, the cover is nearly impossible to get off. I modified my cover to make it two piece, by cutting it in half, and welding a overlapped piece of sheetmetal where they came together. That way I can remove the cover to change the core, and not pull the blower half out.