closed or open chamber?
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From: Independence, MO
closed or open chamber?
to be perfectly honest? there is no such thing, but it is however a name, mostly used in reference to 351C (Cleavland) heads, The 4bbl. Cleavland heads are refered to as (closed) Chamber or QUENCH chamber heads, meaning there combustion chambers are a lot smaller then the 2bbl. heads which are refered to as (open) chamber because there combustion chamber is so much bigger, there fore yeilding a lot lower compresion ratio.
4bbl. Closed (quench) chamber- small cc chambers
2bbl. Open chamber- larger cc chambers
Hope this helps! DW
4bbl. Closed (quench) chamber- small cc chambers
2bbl. Open chamber- larger cc chambers
Hope this helps! DW
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From: Boise, Idaho
closed or open chamber?
More grunt... LOL! 
In visual terms, open chamber is where the walls of the combustion chamber slope away from the valves in a gradual manner and very little of the top of the piston is not exposed to the spark plug when the piston is at TDC.
A closed chamber has a compact design and at TDC much of the piston top is shielded from the combustion chamber.
In visual terms, open chamber is where the walls of the combustion chamber slope away from the valves in a gradual manner and very little of the top of the piston is not exposed to the spark plug when the piston is at TDC.
A closed chamber has a compact design and at TDC much of the piston top is shielded from the combustion chamber.
Posting Guru
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From: Independence, MO
closed or open chamber?
you know if you realy think about it there is no such animal, both heads a machined perfectly flat with the exception of the recess for the chamber it self one of witch is large and ones not, its just a term that got dubed years ago, Just like a (3/4 Race) Cam. There is no 3/4 race cam. whats the specs on a 3/4 race cam? If this be true, can you buy a 1/2 cam? 1/4 cam even? how bout 7/16 cam, better yet 3/8 cam and 3/8's of what? Who come up with the terms we use to refer to things? 
DW
DW
Senior User
Joined: Jul 2001
Posts: 465
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From: Tower MN, Houghton MI
closed or open chamber?
3/4 race cam is an old term from back when stock cam shafts were reground.
The sides of the stock lobes were reduced, to yeild higher lifts, which necitated a longer push rod
there were 4 levels cams, stock, 1/4 race, 1/2 race, 3/4 race, and full race.
The sides of the stock lobes were reduced, to yeild higher lifts, which necitated a longer push rod
there were 4 levels cams, stock, 1/4 race, 1/2 race, 3/4 race, and full race.
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Joined: Aug 2000
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From: PacNW
closed or open chamber?
The visual differences between 'open' and 'closed' combustion chambers are very distinct. In an open chamber head virtually the whole area above the piston is comprised of the machined out combustion chamber. The shape generally matches the shape of the cylinder bore/piston i.e. round.
A closed combustion chamber is much smaller where much of the flat head surface actually covers the top of the cylinder. The shape is usually that of a smaller oval or 'D'.
Open comb chambers are utilized to lower compression ratios and therefore reduce heat during the power stroke thereby reducing NOx emissions. Closed comb chambers mean a significantly higher C.R. and more power.
Most high performance heads are closed type and utilize 'quench' effect to allow high compression with reduced risk of detonation.
A closed combustion chamber is much smaller where much of the flat head surface actually covers the top of the cylinder. The shape is usually that of a smaller oval or 'D'.
Open comb chambers are utilized to lower compression ratios and therefore reduce heat during the power stroke thereby reducing NOx emissions. Closed comb chambers mean a significantly higher C.R. and more power.
Most high performance heads are closed type and utilize 'quench' effect to allow high compression with reduced risk of detonation.
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From: PacNW
closed or open chamber?
The 'quench' effect is the turbulence created when the top of the piston compresses the F/A mixture against the flat surface of the head in a closed chamber head. This turbulence actually helps contribute to a more complete burn which means more power and less chance of detonation despite the higher compression ratio. In addition the 'quench' area of the head runs cooler because it has more metal to absorb the heat which is where the name comes from.
In order to achieve the quench effect you must have a flat surface on the head and a corresponding flat surface on the piston. The 'squish' distance between the top of the piston and the head surface should be in the neighborhood of .040" to achieve optimal quench.
Open chamber heads are by their nature not capable of utilizing the quench effect because they have no flat surface to squish the F/A mixture against. They are much more prone to detonation/pinging problems despite the fact that they run lower compression ratios.
In order to achieve the quench effect you must have a flat surface on the head and a corresponding flat surface on the piston. The 'squish' distance between the top of the piston and the head surface should be in the neighborhood of .040" to achieve optimal quench.
Open chamber heads are by their nature not capable of utilizing the quench effect because they have no flat surface to squish the F/A mixture against. They are much more prone to detonation/pinging problems despite the fact that they run lower compression ratios.
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Postmaster
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From: Harrisburg, NE
closed or open chamber?
oknow that I have down all the terms, how well do gt-40p heads do for quench? I know that there "closed chamber" i've also heard that the gt-40s are turbo swirl, is that turbulence, and does that make them a more efficient head? does more effiecency mean more power while not requiring more gas?
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From: PacNW
closed or open chamber?
I've never seen cylinder heads rated in terms of 'efficiency'. Most heads are rated by the amount of flow they can sustain through the intake and exhaust ports/valves. I would have to guess that the 'turbo swirl' feature is designed to promote a more thorough mixing of the A/F mixture to promote a better burn.
How well a particular head works for quench depends on more than just the combustion chamber design. You need to have the correct pistons as well as the correct deck height. IOW the piston top must have a flat portion which corresponds with the quench area of the head and the pistons need to be set to very close to 'zero deck' since most head gaskets will give you the .040" squish distance you need. This takes careful parts selection and machining.
How well a particular head works for quench depends on more than just the combustion chamber design. You need to have the correct pistons as well as the correct deck height. IOW the piston top must have a flat portion which corresponds with the quench area of the head and the pistons need to be set to very close to 'zero deck' since most head gaskets will give you the .040" squish distance you need. This takes careful parts selection and machining.
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