Quote Originally Posted by mudnut View Post
I did ask about that quite a while ago, and was told that Marks do a bell housing adaptor for the TB42 auto transmission. I was also advised (by Nissannewbie) the FS5R50A would sap too much energy from the RB30 to be viable. Although a turboed 30 would handle it.
Ideally, any energy loss that is caused by a mismatch of torque conversion should able to be corrected by employing the correct diff ratio. And hopefully that should fix any energy loss. I like to think the slightly bigger box ideally shouldn't cause any significant loss of energy, 'cos after all the interior components are near identical, but just slightly bigger. A heavy duty clutch may be necessary to match a high revving RB30 with the TB42 gearbox.

There is a thread somewhere on how to fit an auto tranny onto a GQ RB30.