I measured my dampers circumference and it was 21 inches around. So 21/Pi = 6.68". Thats CLOSE to 6 3/4" but not quite....should I assume it's 6 3/4 or what? I need to know the diameter...is there a more accurate way? My only options are 6", 6 3/4" and 7"...so it's gotta be a 6 3/4" right?

The engine is in the car, the pulleys are the in way.

 

I'd say 6 3/4" (6.75), either that or roll under there with a right angle ruler. and see if you can get a more accurate reading with that. How did u measure the circumference? String?

 

Yes, it's 6-3/4 inch type. They aren't exact in their diameter. An 8" would be obviously bigger. If it's the original engine in the car then it's definitely the 6-3/4" type. That diameter was used in all 3rd gen motors.

 

It was a 350 truck motor, 70s.

But it's almost definately 6 3/4?