Im wondering what all the differences are between the 3.6 (3.8?) and the 4.2L V8. Or if you were able to find a 4.2 from a 94 V8 is it interchangeable without any major modifications?

Hi!

It fits but I don't think the tranny can take the increased torque. If you use it, that is =).

I assume you are referring to an automatic. An engine from a car with an automatic will not fit a manual and vice versa.

A car with a PT engine (3,6) has a tranny marked AKD, ATU or AYU and a car with an ABH engine (4,2) a tranny marked AZG.

I would advise you to check the max allowed torque for each tranny with an Audi-dealer or directly with ZF in Germany who made them before you change the engine.

You will have to replace the ECM as well, of course.