[bcweir]

The M70 and M73 engines are amazingly sophisticated, and even more so for the M73. The E30 being an OBD-I car is much easier to work with electrically and mechanically, I would have chosen the M70 rather than the M73 for a number of reasons:

1) the M70 is electrically and mechanically simpler than the M73, with nearly all of its available horsepower (296 hp for the M70 vs. 326 for the M73). One could easily upgrade the M70 for another 30 hp to make it even with the M73 with air filter, chip, and exhaust upgrades.

2) Numerous systems present on the M73 that are not present on the M70 make wiring much easier (cat pre-heaters as well as added emissions equipment, as well as four oxygen sensors instead of the M70's two).

3) The two engines use two different engine management systems that are not cross compatible with one another - Bosch for the M70, Siemens for the M73, which means components from the two systems are not going to talk to one another.

4) The higher compression ratio of the M73 means you have to run premium fuel. The M70 will run fine on lower octane gasoline with no problem.

I'm not at all criticizing the use of the M73, in fact I am commending the skill needed for this swap. I merely wanted to point out that when doing a BMW V12 in an OBD-I car like an E30, an OBD-I engine into an OBD-I car certainly makes these swaps somewhat easier, relatively speaking. There's still lots of math involved in fitting such a large engine like an M70 to an E30's smaller engine bay. Best wishes!