mrg

A bit OT here. Does anyone remember how the term, 'siamese heads' (ports?), on SB engines came about. ? .. The obvious reference would be to the intake ports being 'siamesed' together. There would seem to have been an advantage to using this kind of arrangement compared to individual port runners. Was the Chevy SB the only engine design to use this port concept? ..

John

L79vette

They aren't truly siamese on a SBC. The runners are grouped, but they remain separated. My 1275cc Austin A-series engine has true siamese ports, as does our 235 cubic-inch Blue Flame Six in the '54. For the inline engines, the advantage is being able to have reasonable sized ports while putting the intake and exhaust ports on the same side of the head. Why they wanted to do that I'm not sure, though I strongly suspect it has to do with making simpler cheaper castings. True siamese is bad for performance because you get one cylinder robbing another.

I've seen pictures of an SBC with the dividers cut out between the intake runners. The caption said this was for a blown nitro application.

Hopefully someone else knows why the SBC ports are grouped the way they are.

SWCDuke

The SB ports are NOT siamezed!

This term refers ports merging prior to the either manifold interface like the center two cylinders exhaust ports on a flathead Ford V8.

Many engines have the inlet-exhaust layout of the SB. On a V8 it allows more equal length inlet manifold runners.

Duke

Marks69BB

Oops - wrong post!

mrg

After all these years, I had thought SB intake ports were referred to as being 'siamesed' .. Must have read some old Hot Rod magazine back in the day and misunderstood the term.
Thanks for clarifying.

John

Plasticman

You might have been thinking of the siamesed cylinders of the 400 SB Chevy engine block.

Or, the writer of the Hot Rod article did not understand the term in ref. to the heads.

Plasticman

FredFlintstone

The Flat Ford used that concept starting in the 30’s although the FHF shared the same exhaust ports for the inner two. The Ford Y-Block introduced a couple of years before the SBC used that setup. In fact if you are not very familiar with the differences between a Y-Block Ford and a SBC you might mistake the the Y-Block for a SBC or vise versa. Which makes me wonder if Chevrolet copied that engine for their SBC. After all, to convince the CEO of Chevrolet to jump on the V8 band wagon was someone installed a Ford engine in a Chevy and took him for a ride. Another thing the Y-Block had back in the 50’s was deep skirts, which is why it was dubbed the Y-Block. Now pretty much all engines are deep skirt now.
Chrysler also used that layout for their small blocks and big block wedge motors but not their Firepower or 426 hemi engines. AMC also used that layout.
Ford broke away from that and went to even spaced exhaust ports when they introduced their famous FE engines for their medium block and Windsor engine for their small blocks in the early 60’s. Now pretty much everyone followed that lead and are evenly spaced for V8 engines.

silver837

Welcome Fred . Thanks for your history lesson. Always nice to learn something new .

larebob

If you take the valve cover off one of our SBC's, you can see some of the reasoning and compromise the engineers needed to make. We have 5 bolts around our cylinders (a 427 Ford, with separate intake and exhaust ports has 4). The push rods need a path, cooling needs to be routed in certain areas, the pattern makers in the casting foundry can't make crazy complex patterns just to crutch some design idea, etc. Most air liners look the same, ditto for military jets - because nature dictates the design to a great degree. A V-8 internal combustion engine needs some similar traits, nature demanded. Maybe the LS or one of the NASCAR designs is at the ultimate pushrod arrangement, but our old SBC sure was a darn good slide rule effort from the wonderful 1950's - the tenderloin of American culture and science.

Skip Fix

The 301 Pontiac motors early 80s had siamesed intake ports and each pair were even different! Why even with the Turbo on the Trans Am they were slow!