Early wedge head squish….

[Truckedup]

Jack Vines may know this… I see that early SBC’s had a squish of around .045. What about the 1949 Caddy and Olds, did they have a reasonably tight squish from the factory? how about the Buick Nail head and Pontiac?

[PackardV8]

First generation Kettering OHV8s were 7.0 - 8.0 compression. The 1955-56 Packard V8 was the first modern high compression design, with 9.5 - 10.0 compression. The blueprint on those was also .045".

FWIW, a bit of SBC trivia. When the 1955 engine production line was up and running, complete engines were randomly pulled and dyno tested. Every one of them was slightly down on power. Disassembly revealed the block deck height was at the top of the allowable spec. The foremen on the broaching line were paid a production bonus and had set up the line to run at max speed and minimum material removal. The engineers lowered the deck height spec to a tighter tolerance and power came back in on target.

[Truckedup]

Do you know if the later higher compression GM engines used a tight squish? I read Kettering thought compression ratios would go near 12-1 if high octane fuel was common.

[RDY4WAR]

My '93 LT1 350 came with 10.4 compression with the piston .025" in the hole and a .049" gasket. (.074" quench) It also has aluminum heads with reverse cooling which helps keep away detonation.

[Truckedup]

Just use a shim gasket and the squish will be about .045.

[Walter R. Malik]

Just for information ... 440 six-pack Mopar engines had 10.5/1 compression ratio with well over a .100" squish and experienced no detonation using the pump gasoline of the day.

[frnkeore]

The '58/'59 Edsel 360 and the '58/'59 352 Ford, T-Bird engine was maybe the top of squish scale @ .036, CH 1.875, 6.540 rod, 3.500 stroke, .031 shim gasket/ 10.170 deck.

In '60 the Ford 352, T-Bird dropped it's CH to 1.866 and the squish to .045.

They also had NO valve relief in those days, just a completely flat top but, the top ring, was down .400.

[Geoff2]

Thev1956 Pontiac 317 had 10.0:1 CR & a wedge head.

[PackardV8]

Thev1956 Pontiac 317 had 10.0:1 CR & a wedge head.

The book shows an optional 2x4-bbl carburetors, 10.5:1 compression, 285 hp @ 5100 rpm, 330 lb⋅ft @ 2600 rpm, was offered in mid-'56, but in sixty-four years since then, I've never seen one.

FWIW, the first-generation Pontiac V8 heads and the 1955 Packard V8 used a true Kettering fully machined bathtub chamber, very tolerant of high compression, but shrouded for breathing. In 1956, Packard changed to a cast dome true wedge. Pontiac retained the bathtub for several more years.

[Truckedup]

Just for information ... 440 six-pack Mopar engines had 10.5/1 compression ratio with well over a .100" squish and experienced no detonation using the pump gasoline of the day.

I was told that the open chamber head was necessary to deal with Nox emissions…The only new vehicle I owned was a 69 Super B 383… it had the open chamber 440 heads, don’t know if the 6 pack used different heads.But with advertised 10-1 compression it was fine with any premium gas..Some guys with fast street B Mopars back then said the closed chamber heads were better..I don’t remember much talk about squish back then..But I knew even less than now…duh…
Jack, the 302 inline 6 GMC I messed with had a deep bath tub type chamber and was prone to detonation …But due to head gasket available, tight squish was not possible unless the piston came above the deck.

[Geoff2]

Six pack used the same heads as the 4bbl #906, open chamber head. The #915 was the last of the closed chamber heads, phased out around 1967-8.

[novadude]

FWIW, a bit of SBC trivia. When the 1955 engine production line was up and running, complete engines were randomly pulled and dyno tested. Every one of them was slightly down on power. Disassembly revealed the block deck height was at the top of the allowable spec. The foremen on the broaching line were paid a production bonus and had set up the line to run at max speed and minimum material removal. The engineers lowered the deck height spec to a tighter tolerance and power came back in on target.

That is interesting, and it makes total since that the production guys would cut as little material as possible for time savings, tool life, reduced scrap from getting too close to lower limit, etc.

[PackardV8]

FWIW, a bit of SBC trivia. When the 1955 engine production line was up and running, complete engines were randomly pulled and dyno tested. Every one of them was slightly down on power. Disassembly revealed the block deck height was at the top of the allowable spec. The foremen on the broaching line were paid a production bonus and had set up the line to run at max speed and minimum material removal. The engineers lowered the deck height spec to a tighter tolerance and power came back in on target.

That is interesting, and it makes total since that the production guys would cut as little material as possible for time savings, tool life, reduced scrap from getting too close to lower limit, etc.

The rest of the story is the relatively wide upper/lower deck height spec was arrived at in negotiations between the engineers and the production management. Production insisted they needed leeway to avoid scrapping blocks. In practice, with a new broaching line, they could and did hit the upper limit nearly every time. The spec was narrowed by 50%.

jack viens

[Truckedup]

A retired GM engineer told me that any change in production was a huge hassle that also involved union reps who resisted any changes that could possibly affect the number of workers or more effort required by workers….

[rgalajda]

This may be a little off topic , but what would you consider the minimum squish for a 1969 BBC with rectangular port closed chamber heads and street use.