Hmm, what is the Zeus head?
This is what Tim posted to the TurboEsprit mailing list this morning:
The Zeus head was introduced in Jan 1993, along with the upgraded head bolts and the composite Goetze head gasket.
The head to block face remained the same from the Jensen-Healey 907 through the Esprit S4s Zeus 910, so any 9XX head will bolt to any 9XX block.
The intake ports were enlarged and re-contoured. The back side of the valve head was contoured to compliment the tulip port design to enhance flow. Standard/ generic valves of the same diameter won't produce the same results as the Lotus-spec valves.
Manifolds will mechanically bolt on interchangeability, but the later intake manifolds are port matched to the larger Zeus port.
The Zeus head's inlet valve diameter was enlarged 1mm over the previous versions (it's the 'big valve' version). The exhaust valve diameter remained the same as before.
Inlet, 907 thru S4, pre-Zeus 35.47 - 35.65 mm (1.396 - 1.404 inch) All, except S4s/ S300
Inlet, S4s & S300 36.37 - 36.63 mm (1.432 - 1.442 inch) S4s/ S300 Zeus head
Exhaust, All 30.73 - 30.91 mm (1.210 - 1.217 inch) ALL
Zeus is the name of the company that cast the parts. When Lotus switched casting vendors, they also re-tooled the head and the block, switching from die cast to sand cast. They took that opportunity to make some running design changes, but none that affected backwards compatibility... except...
The Goetze composite gasket has a compressed thickness that is 0.5mm (0.02") thicker than the previous steel-asbestos-steel gasket (which is no longer available). That affects the overall Zeus engine assembly, and you asked about the Zeus head alone. So the following is FYI, and not Zeus head specific.
All else being equal, that extra gasket thickness raises the cylinder head by that same amount, resulting in a larger combustion chamber. The Zeus engines were designed to work with the composite gasket, so the cylinder block's deck height was cut lower by that same 0.5mm (0.02") amount, and then the liner seats in the block were cut that much deeper in order to preserve the proper liner exposure above the block deck ('nip'). In the end, Zeus engines with the composite gasket end up with the cylinder head in the original design-position, and with the correct nominal compression ratio. However, using that composite gasket on any older 9XX engine results in about a half a point lower compression ratio (8.0:1 becomes 7.5::1). There are no factory alternative, it is what it is.
All the Zeus engine assembly's dimensional differences are in the cylinder block's machining, and the gasket's thickness. Nikasil liners will interchange between pre-Zeus and Zeus engines (GT3 2.0 liter engines are a different set of design options all by themselves).