What is the differance between 455 sd and normal. I have heard sd is the race one but why are the pistons diff and other parts?? are the bore, stroke and rods the same? what sets the two apart. thanks for your help.

The SD-455 was an option on TA's in the early 70's (only 73 and 74 I believe)
During 73 and 74 production, Pontiac only made 1296 Super Duty cars.

it came with:
800 cfm Q-jet, 4 bolt mains, forged rods, TRW forged pistons, provision for dry-sump lubrication, a round port low compression head, dual exhaust and 290 net horsepower @ 4000 rpm.
Basically all the things you would do to a standard 455 to make it a real good motor.

The bore, stroke and rods are the same, just comes factory fitted with performance lower end, would just need a decent cam and intake and a little head work to make a fire breathing beast.