a87 head

Engine, Transmission and related drivetrain.
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guzzirik
Posts: 33
Joined: 21 Dec 2018 23:49

a87 head

Post by guzzirik » 02 Feb 2019 00:39

From what I gather from posts Iv'e read, the peanut head is rare. is there any way a head can be identified from casting #'s or port size?

datzenmike
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Joined: 24 May 2006 12:40
Location: Van. Isle.

Re: a87 head

Post by datzenmike » 02 Feb 2019 08:58

Not that I know of other than using a borescope camera in the spark plug hole. L18 engines, used for barely one year in and around '74, had A87 heads and the earliest use of the L20B in the '74 610 had them. All other L20Bs from '75 on had U67 and the later W58 heads. I did briefly have a closed chamber W58 head.

Open chamber heads form a convoluted dome over the entire piston top whereas the closed chamber heads have a large surface encompassing the valves that is separated from the piston tops at TDC only by the thickness of the head gasket. A closed chamber head is intended for use with flat top pistons that 'pinch' the air between them and the head, violently forcing it into the central combustion chamber and promoting beneficial swirl and turbulence. Where the flattop piston and the head surface are only separated by the head gasket thickness, this is known as the quench or 'squish' area. If you are running any piston type with a dish in it you are really not getting any quench or squish except for maybe a 1/4" ring around the piston tops. The only gain from a closed chamber head is a compression increase. An L20B is upped to 8.9 An L18 is upped to 9 and an L16 looses compression to 8.21


It's my belief that closed chamber heads arrived here on import engines from scrapped Japanese domestic market Datsuns, though some have maintained that their engines are the original ones bought new and never replaced. It's hard to claim ownership for 45 years and know for sure it's never been worked on or had a valve job. Low mileage import engines were a much cheaper alternative to machining and rebuilding a head with worn valve seats and guides. Another thing is, I doubt very much that Nissan would install random closed chamber heads on North American engines as they would most certainly negatively affect the emissions.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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