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From: adm@cbneb.UUCP
Newsgroups: net.auto
Subject: Re: open-chambered motors?
Message-ID: <3038@cbneb.UUCP>
Date: Wed, 13-Mar-85 09:25:35 EST
Article-I.D.: cbneb.3038
Posted: Wed Mar 13 09:25:35 1985
Date-Received: Thu, 14-Mar-85 06:24:35 EST
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Nf-ID: #R:cmu-cs-g:-24900:cbneb:8400006:000:1770
Nf-From: cbneb!wdg    Mar 13 08:47:00 1985


	An "open-chambered" motor refers to the shape/size of the
combustion chamber. Therefore, it is the heads on the engine that
determine if the motor is open or closed chambered. Generally
speaking, an open chambered head's combustion chamber is larger and
closer to a hemispherical shape "hemi" than a closed chambered head.
To give you an idea of the difference in volume between the two, a typical
closed chamber head might be 80-100cc whereas an open chambered head
would be closer to 120-140cc.
	This, of course, is not the whole story. The shape of the piston's
dome (or lack of one) in conjunction with the shape of the head is what
really determines the shape of the combustion chamber. Obviously, for the
same compression ratio, the open chamber head needs a piston with a larger
dome than a closed chambered head.
	Whats really important is which one is better? That really depends
on what you want the engine to do. Though combustion chamber size and shape
have a big effect on the combustion process, I will set aside the discussion
of efficiency, pollution control, and detonation. One of the biggest
advantages of the open chamber is its ability to handle larger valves more
efficiently. As anyone that knows engines, knows, big valves, big cams, and
big carbs mean big power. This is the reason the ultimate open chambered
head, the hemi, can produce so much power.
	If you like to listen to Guy Lumbardo or that Welk fellow, are
worried about the environment and fuel consumption, then I suggest
you go with a closed chambered head, low compression ratio, low
duration cam, and a small carb (you'll get more low end torque).
However, all else being equal, the power difference between a closed
and an open chambered head is quite small.

						Bill Guinn