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Swapping my W58 open for an A87 closed chamber -- spark plug difference?


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Blew a headgasket in my "new" '78 620. I've got an A87 closed chamber head in good condition and plan on throwing it on (why not?)


Wondering if i need to run a cooler or hotter plug than what the W58 runs?


Any other info I should know?



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Shouldn't have to and here's why. The design of the closed chamber head is such that the combustion chamber is much smaller than the diameter of the piston below it. This means that at TDC there is only the thickness of the head gasket between it and the head surface around the base of the combustion chamber.  (not strictly true as the L20B has a dished piston and this would apply more to a flattop piston) The air in the cylinder is pinched out from between the piston and the underside of the head and this induces beneficial turbulence and swirl that further mixes the fuel and air. The mixing prevents lean and rich areas and it will burn more efficiently. Lean areas will run hotter as there is less cooler atomized fuel to absorb heat. Rich areas will burn incompletely and leave soot. Turbulence will cool the piston top and all of the combustion chamber including hot spots like the spark plugs, and exhaust valves. 


A closed chamber head is much less prone to heat caused detonation that an open chamber head with the same compression.



You know that only the W58 has round exhaust ports.right? An L16/18 exhaust manifold is known as the cast iron header.

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