from a box that gives you 3 turns lock to lock? I've read that 12.7:1 gives a good response but the person with a kit that I'm looking tells me he doesn't know the ratio but it takes 3 turns to go from lock to lock.

The other piece of the puzzle is the range of motion of the pitman shaft.

You can rig up a cheap grade school protractor on the pitman shaft and determine the sweep of the shaft in degrees. (It will be something like 60 to 85 degrees.) Now you take the total number of turns of the input shaft (the guy stated 3 turns lock to lock) (3 times 360 = 1080) in degrees and divide the pitman shaft sweep into it.

In order to get to a 12.7:1 ratio the sweep should be 1080 divided 12.7 = 85 degrees. A sweep of 85 degrees is good for most Chevelles.

The three turns lock to lock is the quicker ratio GM box that was generally used on the Corvette. I put them on all my Chevelles and really like them.

Most suspension parts warehouses are going to use the "turns lock to lock" method of defining a box rather than the "ratio" method, just 'cause it's simpler.

Here is a little math for those 3 turns lock to lock people! The first number is the typical pitman shaft sweep for a typical car model. The second number (360) converts angle to number of turns. The third number is a typical power steering gear ratio manufactured by Saginaw Division. The equation provides the total number of full lock to full lock turns of the gear input shaft (also steering wheel turns).

Chevelle (89 degree pitman shaft sweep) 89/360 x 12.7 = 3.14 turns L to L

Monte Carlo (78.5 degree sweep) 78.5/360 x 14 = 3.05 turns L to L

Camaro (64 degree sweep) 64/360 x 17.5 = 3.11 turns L to L

As you can see, a box with 3 turns full lock to full lock can have ratios all the way from very quick (12.7 :1) to very, very, slow (17.5:1) just depending upon the sweep of the pitman shaft.

(Obviously the length of the steering arm on the spindle and the length of the pitman shaft all have an effect as well.) But just specifying the number of turns full lock to full lock is not a good way to specificy a power steering gear.

JIML82