170 or 225?

I have driven both the 170 and 225 over the years, mostly in '60-'66 "A" bodies and agree with all that say how you intend to use the car is what matters most. If just a fun, daily/street driven, driver the 225 is the better choice due to it's increased low end torque in my opinion. You can leave on a lot of faster cars from a static start (not rolling), at least to the other side of the intersection, even if it's bone stock. For "performance" either the 170 or 225 can be built but will cost more than a V8 usually and will rarely perform as well. Not to mention a built slant 6 uses nearly the same amount of fuel as a warmed up V8. They loose all economy in "hot rod" mode. I still enjoy crushing the tuner guys in a stop light grand prix with my hard launching, bone stock , 225/auto. They'll always catch you and pass but they are getting a long look at my taillights while doing it !!