21V/V52/85E Heads vs OWO

The W series heads have new water passages for the redesigned W series block. I think the OWO heads flow better
http://z31.com/wiki/doku.php?id=resources:w-series
https://z31performance.com/forum/z31…e-head-casting
https://z31performance.com/forum/z31…s-section-pics

Yea , thats the same TSB I saw, what im talking about, if you look at the heads and the block there will be a casting number (21v, v52, 85e). What im trying to figure out is what do those casting number signify. For example : chevy 903 heads vs chevy 624 heads. The 903's were vortex heads. Did nissan do the same type of labeling

Well, they did all come on different models/cars but there aren't any real major changes to the heads like your chevy example. 21V are the early A/B heads. The V52 heads added the extra water passages for the W engine but are otherwise identical to the 21Vs as far as I can tell. The OWO heads from the 3.3 are a much cleaner casting and appear to have higher/more floor on the intake port. They also have 10mm exhaust studs. The 85E heads came on the Maximas (others maybe?) and I've heard are the same casting as the OWO, but I have no first hand knowledge to verify that claim.

OWO is the cleanest cast, and has a higher flow potential overall when ported and polished. I would advise against using them with a NON-W series block.