Springing a 3.2 conversion, Need numbers for the rear Options

[worn]

I have gotten to the point where I need to consider the spring rate. The rear trailing arms are in with true 5 lug hubs, 911 brakes, and some reinforcement. The shocks are bilstein sport. It is a road car with 16 in wheels running no flares so the tire size will be 205.
I have the original springs from the 1972 four cylinder donor. So ladies and gentlemen, please help me with shopping, or not shopping. Thank you!

[shoguneagle]

I think one has to consider the total car and since it is going to be for road, the possibility of stressing the rear suspension if heavy spring loads are going to be used.

I have a 74 914 which has been converted to 1987 3.2 Carrera, complete 911 Carrera front suspension, Doc Evil rebuilt transaxle with flipped H gear, 911 front engine mounts including Mr. Johnson's mount, solid rear transmission mounts, 911 Carrera brakes all four corners, red adjustable Koni's all four corners, 110CV joints and drive adaptors with Sway-A-Way axles, interior stress kit, Brad Mayeur Long stress kit, boxed rear suspension mounts, rear adjustable spring perches, 180# springs, front and rear suspensions mounted Elephant Racing brass/bronze insert bushings with zert fittings, front turbo tie-rod kit, 911 brakes including rotors all four corners, modified 911 E-brake, rear suspension ears reinforced, rear suspension mounting stressed to fire wall, and numerous other items I have forgotten about. Some of the other items involve rear stock sway bar, 21mm aftermarket sway bar, 21mm front torsion bars, 17 inch Cup II rims with 235/45 9 inch in rear; 205/17 7 inch in front, etc. In sum, the car DOES NOT HAVE ANY FLEX and it is really stiff (no roll cage).

I changed the car suspension from what has been listed above to: front torsion to 19mm, rear springs to 19mm, 21mm front sway bar set to lightest, stock rear sway bar installed, all four corner Koni's set on light setting.

What is the meaning of all the information above? First, you have to consider like you are doing the suspension type, mounting stressing, driving style, brakes, etc. All this will determine how you will build the car.

What I would I do differently? I would determine what I wanted the car for and stay with it. I originally built for both road and racing; it can be done but in my case I forgot to keep everything defined for the road and the race track. I got to building and ended up with a car better for the track than the road. In sum, I would stay with the road driving and use that setup for occasional race romps.
911 or modified 914 with 19mm front sway bar, 19mm torsion bars, Adjustable Koni Reds/Yellows or Bilsteins all four corners, original sway bar in rear, 120-140# springs in rear. I believe the 914 brakes are more than adequate in stopping the 3.2 when properly built and maintained (19mm brake master cylinder ???) and very good top end brake pads.

I would box in the rear suspension console for distribution and strength. I would be very careful in welding up the car body seams. We are now getting into an area which has to be understood and carefully defined because you are now affecting the roadability of the car and taking it into racing type driving.

I am just a "frustrated, long winded engineer" who enjoys his hobby of building a 914. They are truly great cars and thus making a very enjoyable hobby.

The are considerable threads on this site and people who can give you better advice. Do you research, listen, and understand to the level where you feel comfortable in building your car.

Hope the above helps.

Steve