Yup, 3rd gear in the Saginaw 3 speed tranny is a killer power robber,or maybe I should say accelration killer,,,maybe w/a turbo,it would not matter as much.
I remember when I use the Saginaw 3 speed, I used to have to fan the clutch to get the engine back into the power band when going into 3rd gear.
A wide ratio Muncie pulled much better than the 3 speed when I made the swap.
This is when I raced @ LACR 3000 ft + altitude & ran 14.3's just after I removed my T50 5 speed trans from a Chevy Monza.
BTW, the BW T50 5 speed trans are very weak, I broke both of them in a short time.
MBHD
