Got a free set of 31s and decided to lift my Jimmy.
Got a brand new torsion key kit for 50 clams with brackets for the rear.
How effective are these torsion key lifts?
Will it have any negative affect when off roading?
Will this kit be ample and leave clearance once I install 31" tyres?

thanks in advance

 

Using replacement torsion keys is common and effective, within limits. The largest lift people typically do with this technique is only about 2 inches. There is a kit from Rough Country for a 2.5" lift. This kit includes the hardware to remount the front axle at a slightly lower position so that the CV joints are not overly deflected.

As for using 31" tires on a non-ZR-2, this can work, but there can be some small fitment issues. I had a tire shop trial fit 30s and 31s on my Blazer and the tread of the larger 31s would hit the frame-rail before the steering wheel got to full stop. People also have reported that the front fender wells will need their edges turned. I went with the 30s so as not to lose much in the way of effective differential gear ratio and to avoid the fitment issues.

With any lift with torsion keys, i.e., not going for the large 6" lifts and solid front axle swaps, people report that the upper ball joints will wear out faster if you are using the OEM upper control arms. I was able to install the upper control arms from the RC 2.5" kit so to try to avoid this problem. I've only had to replace one of the upper ball joints over the last 6 years or so.

There should be a "sticky" thread on doing lifts on our Blazers.