BLOCK AND HEAD
First off, you need to decide what head you are going to run, the P11 or the P12.
You need to think about the bottom end you will use, and if it’s up to the task of the turbo/cam set-up you plan to have. If you use factory DET pistons, you are limited with your cam choice — the pistons don’t have notches for valve clearance as a set of aftermarket CP pistons does, like those pictured. The extreme lift on these VE cams is no joke.
The oil pump from your DE/DET engine is not ideal to use with the VE head. Although there are no fitting issues, the DE/DET pump doesn’t provide enough of a consistent high oil pressure, which is needed in a VE engine, so a VE oil pump and front cover should be used. That means the crank pulley needs to have 3mm machined off the rear and a VE oil pump spacer/pump driver needs to be used, as it is longer.
The head oil drain at the rear of the block on the SR20DET engine needs to be blocked up, and there are a few common methods to do this: hammer in a bung (one which doesn’t protrude over the block height), weld up the hole and have the block decked and smoothed, or drill and tap the hole and screw in a suitable bung.
Because the head is already off, you will need to replace the head gasket before the head goes on. DET head gaskets aren’t suitable for this application, but VET items are. A factory-rated SR20VET head gasket will only cost you around $80 through Pten, and they’re strong enough for 447kW (600hp). If you are hunting power and want some serious security, by far the best option is the range of head gaskets from Cosworth. They’re multi-layered steel and come in a range of thicknesses — 1.1mm, 1.5mm, and 1.8mm.
The valves and valve springs will need to be replaced if you plan to use the engine for racing, or constant high-rpm abuse. The factory exhaust valves can’t handle racing heat conditions, so they can be a weak point.