In NSW, it has to go by the modifications guidelines which can be found on the RTA website. An engine up to XXXX capacity can be legally engineered into XXXX chassis weight. They determine that by the heaviest model (fully optioned with auto, etc...). The engine, mounts, turbo all have to adhere to certain clearances and like PIGDOG said, only an engineer can tell you, even then i doubt he would tell you the specifics as its trade secrets so-to-speak.

The CA18 can just fit in a 1200 coupe because its so light. The difference is whether or not the engine is a turbo. An N/A SR20 are legal (after being engineered) but a turbo ones are not. You can put a turbo on it after be ing registered but if u get pulled up and the cop knows wat to look for... your dead in the water with a hefty fine.

Take PIGDOG's advice, take your car to an engineer and say whats the biggest engine i can get to be legally registered in this. He should tell you, then its up to you to find a shop that knows what they are doing to get the clearances right and therefore, be able to be engineered. :)

-Steel

**I'm not sure but i THINK there is a loophole for utilities in the power-weight equation. Will see if i can find out and get back to you. :)