I was seriously considering the C20XE or C20LET a few years ago, when I had a 2.0 carlton. Never came to a realisation, thoug...
But I have learned that the C20XE is not the best choise for a heavy RWD car such as omega. If you compare X20XEV to C20XE, you will see that C20XE is more powerful (136 to 160bhp usually), but also aou must consider that X20XEV has more torque (210 Nm compared to 190 Nm in C20XE), especially in lower revs. Torque is important in heavy car.
It is not without a reason why the C20XE wasn't sold in a carlton. If you wanted economy and realibility, you could have a undestructable C20NE, and if you wanted power, you could have a 2.6i or 3.0i or 3.0i 24v. The low torque C20XE just wouldnt make much difference compared to C20NE in a heavy RWD car (propshaft eats some of the power).
I have explained this on a carlton, but it is the same thing with omega...
The only advantage with C20XE in power and performace over the X20XEV would be in high revs, bout you will alsto lose low revs driveability.
The real gain would be the C20LET, but it is not easy to fit one, because turbocharger interferes with engine mount. But at least, due to the RHD setup, the steering box is not in the way (in europe, this is one more problem).
Usuall problems with instaling C20XE or C20LET in a omega:
- exaust manifold interferes with engine mount (can be solved by adapting the X20XEV manifold in C20XE case)
- plastic SFI box might interfere with bonet - can be solved by installing a power cap
- ECU loom is to short, and directed in a wrong dirrection (towards the lihgts) - either lenghting the loom or puting the ecu in the bumper area.