I picked these up second hand and wondered if a stock 911 would use torsion bars this big. I assume that there Porsche parts because of the part numbers stamped on the ends.
I also noticed that one was stamped for the right side, the other isn't stamped. Should I assume that the unnamed one is the left?
The car is a dedicated track car and I've been using the stock 914 bars. Time to beef up the suspension.

I ran 23mm front torsion bars on my track duty 911SC. Looking back, I either should have run larger rears (I ran 30, but should have run 33's) or smaller fronts (say 22 vs 23).

Assuming these are larger than what you already have, how will you upgrade the back end?

Not sure. When I did the 5 lug conversion for the 3.2 six I bought a 1985 Carrera front suspension and went with the torsion bars that came with. They run really nice. At the time I figured I would have greater choices with 911 bars than 914. So far I like a lot.

I do know there are more splines on the 911 torsion bars compared to the 914. They are not interchangeable.
I used a '71 front suspension from a 911T when I upgraded to 5 bolts...

They will be way stiffer than a stock bar and like the others said, you need 911 A arms.

I have 911 A arms. Just cleaned them up today. Need to weld a set of u-tab for my swaybar next. Cant wait to see the difference at the track.

Both the 914 and 911 control arms support 21,22 and 23mm torsion bars. The only advantage of 911 control arms is the stock torsion bar is 18.8mm versus the stock 914 torsion bars i think are around 17. Most people upgrade both types to 21mm for street and autocross. Typically only dedicated track cars use 23mm. I tried 23mm torsion bars with my 914-4 control arms and it rode like a rock. I switched back to 21mm.

My rear springs are 150lbs. I like to change one thing at a time, hit the track and go from there. Do you have any advise on rear spring size? I'm all ears.
I've also found this on info on Elephants site. Its for there Von Shocks but it implies that you should match your strut inserts to your bars.
Oh, my current bars are stock 914s.

The automotion catalog and an old Porsche magazine that featured the winning Brumos GT car said to run 180 LB weltmeister rear springs with the 23mm torsion bars. Now with Eibach coilovers people are running 225 LB or greater.

Here’s the Automotion chart from an old catalog
Click to view attachment

Brumos Recipe
Click to view attachment

Damn Steve. Thanks for that info.

nice articles!

Not sure where you want to go with the rear spring rates but I would presume more, maybe around 250#? Also depends on how you like car set up (stiff vs soft). I imagine that if all you did was improve the front you would get a lot of understeer. As you mention, its a bit of in for a pinch, in for a pound, as you will find yourself likely chasing shocks, sways and springs to get it where you want. Also, I imagine if running an LSD that would impact handling.