basically, they're strong d-series motors that can be bolted up to your existing d-series axles,transmission,clutch,mounts,wiring,etc.
they're 1.6 liters with 75mm bore and 90mm stroke
they come in SOHC and DOHC versions. most of the time people refer to ZCs as the DOHC versions, which make 125-130hp.
Honda stopped making them because the d16z6 sohc vtec was cheaper to make, made the same power, and weighs less.