Silly question for experts
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Instructor
Joined: Nov 2004
Posts: 232
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Silly question for experts
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.
Drifting
Joined: Oct 2008
Posts: 1,936
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From: Rochester Hills Michigan
When they designed the 396, they went to o-o-o-o to reduce hot spots in the cylinder head.
with Bill... Cost is big driver
Safety Car
Joined: Mar 2009
Posts: 4,191
Likes: 951
From: Corpus Christi, TX
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.
Racer
Joined: Mar 2008
Posts: 448
Likes: 18
From: Tucson AZ
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."
"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."
