mjs@cmu-cs-g.ARPA (Mark Stehlik) (03/10/85)
OK, I've done a fair amount of work on my Mopar and have a good feel for things mechanical, but I have no idea what an open-chambered motor is. Hemis, yes; canted valves, yes; mild cams, yes; but open-chambered? Sounds like something from Humana Hospital. Could someone out there in net-land enlighten this poor soul? Thanks in advance. Mark
hkr4627@acf4.UUCP (Hedley K. J. Rainnie) (03/13/85)
Open-chambered is a term peculiar to Rat motors. It distinguishes the two types of head design. The closed chamber design was introduced in the original Chevy 396 Big block in '65 and continued as the standard head for all big blocks. In 1969, Chevrolet introduced the open-chamber design in 1969 for the ZL-1 aluminum racing motor and upgraded the L-88 to open chamber heads. The open chamber heads have redesigned water jackets allowing the designers to unshroud the spark plug and basically remove a great deal of material from the chamber. Thus, they flow considerably better than the closed-chambered design. In the seventies, Chevy installed the open-chamber on a street engine, the LS-6 454, producing 425 hp. Chevy also made iron versions of the open chamber in the seventies. The open chambered head, since it has a larger chamber volume, requires a higher dome piston to regain the same compression as a closed chamber head. The open chamber additionally has more efficient combustion characteristics, requiring lower compression for equivalent power and produces lower emissions. Why don't I have them on my 427? They cost an arm and a leg. (signed) Speed Racer p.s. For those who know, please correct my facts on the open chamber head. p.p.s. Most of my fact relate more to the Corvette than all of Chevrolet.
adm@cbneb.UUCP (03/13/85)
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
pmk@spuxll.UUCP (P. Kelliher) (03/21/85)
It is amazing how so many people are so narrow-minded as to think that the automotive world revolves around the Chevrolet Bowtie. All I have heard about is Chevy this, Chevy that. There are a lot of us out here who prefer Ford and Chrysler products to your 'Vettes and z/28's. You might be interested in knowing that open-chambered and closed-chambered heads were on the Ford 351 Cleveland motor, but then again you might not. Keep your 'Vettes and z/28's; I'll take a Boss 429 Mustang or a Hemi Challenger any day. Those are the cars with real class. P Kelliher AT&T-IS S Plainfield, NJ
hkr4627@acf4.UUCP (Hedley K. J. Rainnie) (03/27/85)
(Concerning the previous message) Right, and how many street Hemis were there? 500? And how many Boss 429s? 10? The Chevy Big block is the only truly streetable of these motors and the only one you can really buy and run. And of course, only Chevy has the Corvette to stuff their motors in. You want to talk low-volume motors, I could go on about the Chevy 510 Aluminum Can Am block and so on. Speed Racer p.s. Which is not to say that the SOHC Ford 427 and other exotics are not fun, but let's be realistic.