Home built rack and pinion+ coilover build.

HemiDenny said
Sorry...but you ackerman thinking is incorrect...

Please look at it this way....extend an imaginary line from the center of the rear axle housing thru the lower control arm ball joint....whether you are engineering a front or a rear steer system, the outer tie rod should fall on that line.

You are correct regarding the length of the steering arm...it drastically effects the turning radius.

Keeping it real!

Maybe I chose the wrong terms to describe what I meant. The imaginary line that runs through the center of the rear axle, then the center of the lower ball joint, then the tie rod end for proper Ackerman, doesn't change. But as the length of the steering arm changes, it affects the position of the tie rod end because on a front steer it has to be further outboard to stay on that line the longer the steering arm is. That is one of the reasons I said the length of the steering arm needs to be chosen first. To establish one of the axis the tie rod end will have to be on or close to.
I measured for total toe today, not just one side. I got very close to zero toe change, but it still toes in at both top and bottom a bit, showing the need for even longer tie rods. The rack is definitely going to be shorter, At least four inches shorter or 21 total inside to inside tie rod ends. I may go twenty, as there is a ready to go unit built on 20 inch centers. That extra 1/2 inch tie rod length per side out to take care of the little bit of toe in at the top and bottom of travel.
Thanks for the measurement RGP266
I don't see a stock 73 up disc brake setup having enough room with the measurements of only 1 inch+ to allow for Ackerman . If I figured it right, there would be zero Ackerman with the tie rod right up against the rotor, or 1/8 inch away. Also, the rack would need to be very narrow at about 19 inches. The one in my racer with zero Ackerman is 18.