I'll just cover the 4 cylinders, as I'm not too hot on the V6's... although they are also a fairly straightforward swap and great for towing caravans.
For starters lets stick to engine codes, for those of you that don't know
C20NE = 2.0 8v
20XE = 2.0 Early "redtop"
C20XE = 2.0 Redtop with a cat
C20LET = 2.0 Turbo
X20XEV = 2.0 Ecotec
Remember, if the spark plug cover is L-shaped, it's a 20XE or C20XE
even if it says ecotec!
C20XE/20XE are the same engine for the purposes of engine swaps discussed here! Ecotec = straight spark plug cover.
I'll split the conversions up into different areas, and deal with each of them separately.
Engine/gearbox mountsAll 4 cylinder Calibra engines have one engine mount. It's the same on all engines, so no need to swap it but use the one in the best condition. The gearbox has two mounts. I believe these are all the same except possibly the F28's front mount.
Here you see the engine mount used on C20NE, C20XE, C20LET and X20XEV
Gearboxes and driveshaftsAny Calibra gearbox will fit any Calibra engine! As a guide, you're best off with an F20 for anything non-turbo, or an F28 for a turbo or V6.
Use a flat flywheel for a more responsive engine. Downside is it wont have as much momentum for launches and it wont be as smooth. Use a pot flywheel for added momentum and smoothness, but less response.
All the C20NE, XE and XEV driveshafts are the same, and will work with either F18 or F20 gearboxes. All the speedo cables just unscrew and swap straight over. The clutch cables are even easier. Beware, some gearboxes (ie some F28) are electronic speedo drive. This means you'll have to swap over the wiring and speedo clocks too. If possible stick to a gearbox of the same type you already have.
The F28 has a shorter O/S driveshaft because of the transfer box too, so you need this on a 4WD car. If converting the F28 to 2WD, use any NE, XE or XEV O/S shaft along with your 2WD conversion kit.
Fitting 4WD to your 2WD Calibra
It's do-able, but it is a fair amount of hassle and involves cutting up your floor. Do a search for Peachprformance on MIGWEB. He has a very good thread on this conversion.
Non-turbo Calibras do not need 4WD.
C20LET Calibras do need 4WD, so it doesn't make much sense to fit a C20LET into your 2WD Calibra. Just buy a Calibra Turbo. It's cheaper, easier and you get more benefits as well.
Fuel feedsThe two fuel rail unions are the same on all 4cyl Calibra engines, there's nothing to swap here, just dont get them the wrong way round on the rail.
ECUUse the ECU from the donor car. They all mount behind the drivers footwell kickplate. If the donor car has an immobiliser, you need the transponder ring and key from the donor car, OR you need to chip the ECU in the case of the C20LET. C20LET PK and PJ code ECU's are non-immobilised. HD ECU's
ARE immobilised.
A non-immobilised C20LET ECU
Wiring loomUse the engine wiring loom from the donor vehicle. Where this reaches the drivers footwell, there are three plugs to connect to the car loom. Plus the giant plug for the ECU, and the vacuum pipe for the ECU map sensor on a C20LET. Don't touch your car loom, or the loom for the battery/alternator.
The engine loom passes through this grommet, next to the O/S suspension turret
RadiatorsNE, XE and XEV radiators are very similar if not identical. Keep what you have already, and use the pipework off the donor engine if different (the thermostat to the top of the radiator varies). It is also worth noting these radiators are a good upgrade for a C20LET engine that's no longer using it's factory intercooler.
ExhaustUse the manifold and downpipe from the donor car. If it mates to your existing cat, all well and good. If not you may need to change the cat as well.
PowersteeringAll C20NE, XE and XEV pumps are the same, so take your old engine out with the pump attached. Put the new engine in (with it's pump attached) then just connect up the two PAS pipes and you're done.
Standard Calibra PAS pump
Odds and sodsUse the airbox from the donor car. When swapping an 8v for another engine, you'll need the throttle cable from the donor car as it has a different fitting on the end.