n1kon

Is there a reason GM decided to Siamese the exhaust ports on SBC heads. Why did they go with o-oo-o and not o-o-o-o? Are the benefits to the spacing? Just curious, I searched but could not find the answer. Just wanted to know why.

mashinter

My guess: Cheaper exhaust manifolds?

When they designed the 396, they went to o-o-o-o to reduce hot spots in the cylinder head.

66since71

with Bill... Cost is big driver
I'd add that the layout certainly made carb heat and coolant routing easier to manage, too.

Harry

Avispa

.....and then they messed up with the siamesed intake ports. The ones that open toward the center of the cylinder flow much better than their neighbors that flow toward the cylinder wall. @#%#$ Ford basically stole the BBC head design and then fixed the intake port problem with their Boss 302 heads.

Who knows what runs through the minds of engine designers? Mid 60s and early 70s Oldsmobile V8s heads had REAL siamesed center exaust ports. There wasn't even a wall between the ports, just one big rectangular outlet.

bdhulderman

Here's what I found, makes sense to me.

"In the original SBC design done in the early 50's COST was a major driving factor. Siamese exhaust ports allow an exhaust manifold with only three branches, which means a simpler core for the casting. It also uses fewer attaching bolts, and has fewer pads to machine on the exhaust flange of the head. Overall it's also lighter, and therefore cheaper to make. Remember the first SBC was about 160 gross hp at the flywheel."