Yep, I tried it on my 98 ZJ 5.9, the more you shorten the runners, the higher it moves your powerband. For max torque, I would not advise shortening them much at all, if any. What I ended up doing with mine before I went to the hughes FI airgap was making an angled cut, just opening up the angle a little without shortening it. Then I used a burr bit to smooth EVERY edge down in the whole manifold, and ground off all the casting excess, then installed a hughes plenum kit to end the leaky gaskets.
IMO, negligible gains for all the work involved. Ended up ditching it a few months later for a hughes FI airgap intake. A nice tune and some adjustments to the transmission to let it shift at 5600 and that thing would roll. There's so much that can be done to a magnum motor, and I've done near bout everything except stroke one. When I was done with cam, heads, headers, exhaust, intake, injectors, TB, CAI, 1.7 roller rockers, tune, I had a jeep that ran close to 5 sec 0-60s, and towed the boat like a champ. For not a lot of money, really.
