I have a hard time believing that the cast iron manifolds are the weakest part of the exhaust system. The rest of the system is thin walled tube.
You won't be a non-believer if you examine one of these manifolds closely. The casting between the front two cylinders is very thin and eventually fails. Mine was broken there in two spots at about 48k miles. It's important not to over torque the two downpipe bolts at the manifolds. The joint there is not gasketed and designed to swivel. Bolt torque is only 20ft lbs.
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'09 JKRU. 4" Teraflex long arm, Teraflex R44 housing, Teraflex / Fox Resis, Poly Performance skids, Nemesis Billy Rockers, Nemesis flares, 37" ATZ P3s on 17" 5x5.5" Trailready HDs, Spyntec hubs, Teraflex BBK, Mopar BBK master/booster, Superior front & Alloy USA rear axle shafts, CTMs, Reids, Synergy drag link & tie rod, WTOR hydro-boosted steering, 5.38s, TF Dual Rate front bar, TF bumpers, Warn Powerplant, Tom Woods shafts, AA xfer case cable, Kilby canister relo, RH4x4 cage.