Single Turbo '65 Valiant Build

A T6 turbo frame is about 12X10, as big as a car battery! Also the LS guys running that turbo are using a head that flows 240ish out of the box, >[email protected] ported... with the 318 (302) head flowing [email protected]. Sell it for $$$ and get a smaller $$ matched size. I dont think a 4sp would benefit a turbo, youll never get it to spool in that low first. They like to push on something, like a shorter rear gear. 1:1 final is the same in both trans.
Just to clear things up im basicslly just using the block. Im planning on running different cylinder heads. just not quite sure yet. In your opinion what should i look for in turbo size?.