Hi All
I purchased a bunch of engine parts from Gene, 64Rocket, and that included a 403 short block. The engine has been rebuilt at some point and has pistons with shallow dishes in them. I'm thinking about adding heads and putting it in my 1979 GMC pickup for a daily driver/parts chaser. Other than drilling out the head bolt holes to accommodate the larger head bolts on a 403, what else would I need to do to install a set of big block heads on it? I remember a post where Joe_P suggested using big block over small block heads to get the larger valves. I believe that was because the 403 small block can move about the same amount of air as a big block 400. I do have a set of Ka heads that have been rebuilt that I could use. Is there anything else I would need to do to it? Will the ports on the big block heads match the small block intake?

 

The intake port matching is the issue here. All I have read said you would need a small block Performer RPM intake that has enough material to port match the heads.

 

Ideally one would port match but it’s a boatload of work, especially on a dual plane intake. I haven’t port matched intakes on a few SBO’s with BBO heads, never noticed or had any issues. Ideal? Maybe not. Problematic? Not at all. FWIW I would think the little, potential velocity drop at the connection would only matter in a harder core build where every little thing matters. I certainly wouldn’t run it the opposite way - BBO with SBO heads but why would that ever be done anyway? I always used BBO intake gaskets.

 

The SBO intake will have runners that are smaller than the BBO ports. That sort of expansion step will still cause flow turbulence, but not as bad as the other way around. Port matching aluminum intakes is not that big a deal with a die grinder. The OL4B also has enough meat to match up in addition to the Performer RPM.

 

If it’s going in a pickup…will it be used for low rpm towing and a work truck?

if yes….then early small block heads is exactly what you want. with a dual plane , small runner intake like a factory style.