the fast ratio pitman arms were designed for cars that were going to be used in specific race series. can't remember which but one presumes it involved going left most of the time.
a sector based steering box is fast in the middle and slower towards the ends of travel. due to the way the pitman arm interacts with the cross link.
the twist of the sector is linear but the movement of the pitman arm stud in the cross link decreases the further away from central it gets (i.e 90*/ perpendicular to the cross link)
this is the opposite of what is built into modern steering which favours slower in the middle, and faster towards each lock. This cuts down no. of turns lock to lock. makes it easy to go straight, harder to veer wildly off course, or roll, if you jerk the wheel...
modern steering is slow in positions that favour going fast, and fast in positions that dictate going slower, like parking
if you extend the pitman arm. you make the system even faster in the middle. something you may not want..
if you never drive straight this is not a problem, its also faster either side of off centre, this is good for circle track racing. i.e the steering is now as fast off centre where you do most circle track driving , as it was in the centre as standard. It is now fast in a position that allows you to traverse a circle or oval race track. and very fast straight on where you spend little or no time when circle track racing.
a steering box that is too fast in the middle makes it much harder to go straight, and adds to a feeling of instability. you can offset this a bit by whacking in loads of positive castor and paying attention to toe in, but that is more expense.
if you have manual steering and you drive it on the street 90%
choose a ratio you want and use standard pitman arm
if power steering you already have 14.5:1 or thereabouts. and you don't feel the weight of it because its power steering...get a smaller steering wheel.
In my view
better to have manual 16:1 and standard pitman
than try to gain the same ratio with 20 or 24:1 and a long pitman arm
there will be cars and people who have balanced ratio and pitman arm length perfectly for what they want to do i'm sure....but for most of us easier to keep it simple
think about it from a leverage point of view
a sack of gravel:- That you can lift with 1 hand close to the body, would be impossible to lift with one hand 2 foot away with your arm out stretched.... leverage too much for you shoulder
longer pitman you make it harder on the steering box internals and easier for the wheels to knock the steering wheel out of your grip
Basically easier to get busted fingers if you hit a hole or curb....
you need your hands to help you get out in a crash...
Dave
