Turning a Junkyard 6.0 LS into a 600-Horsepower Stroker
Throwing speed parts at stock engines is about as pure as hot rodding gets. From stacking carburetors on utilitarian flat-head Ford engines to bolting a big blower on a world-weary small-block, the recipe is the same: add more power, until something breaks. The Hemmings crew followed suit on our 6.0-liter LS build, adding high-flowing Air…
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Throwing speed parts at stock engines is about as pure as hot rodding gets. From stacking carburetors on utilitarian flat-head Ford engines to bolting a big blower on a world-weary small-block, the recipe is the same: add more power, until something breaks.
The Hemmings crew followed suit on our 6.0-liter LS build, adding high-flowing Air Flow Research (AFR) heads, a bigger camshaft, and a high-flow intake manifold to a take-out 6.0L LS. It was an easy road to power, but unfortunately the main bearings on our mileage’d up core engine weren’t up for the task and rotated themselves 360 degrees in their saddles at our first dyno session. Oops.
Fortunately, quitting isn’t in our DNA, so from the ashes was born a 408-cu.in. stroker that packed more displacement, more power, and a killer aesthetic perfect for any hot rod. Follow along as we take the engine from bare block to 600-horsepower hero.
After the core engine spun a main bearing on the dyno, we pulled it completely down to a bare block and sent it to Dougan’s machine shop in Riverside, California. The engine was treated to a bore, hone, and align hone. The latter was to make sure the bearing saddles were properly round from the dyno carnage and to accommodate stronger Summit Racing main-cap fasteners.With the engine back on the stand, we checked that all clearances were within spec. Dougan’s machined the block perfectly and no additional changes were needed. Next it was time to hang the higher compression forged Mahle PowerPak pistons on forged Summit Racing Pro LS series connecting rods.With the rods and pistons hung, we gapped all of the rings and installed them on the pistons. The rings were gapped at .018-inch and .020-inch, respectively.Next came the main bearing shells. In this build we used King bearings with an extra .001-inch of clearance. The main caps are held snugly in place by a Summit Racing main stud kit.With the bearing shells in place, the forged Summit Racing crank was lowered into the block and the caps torqued down.Once the crankshaft was in place and the mains properly torqued, the Summit Racing Pro LS connecting rods could be installed. Note that the large chamfer in the rod faces the fillet on the crank journal.The rod bearings are also directional with designated “upper” and “lower” shells.All the Mahle pistons were installed using a Summit Racing tapered ring compressor sized for our 4.030-inch bore; the Summit rod bolts were then torqued to spec.One thing to note for first-time LS builders is the orientation of the main caps. They can easily be reversed and doing so will cause the bearing bores to be out of round; a damaged crank is soon to follow.With the short-block complete, it was time to install the Summit Racing LS Pro camshaft and lifters, along with the AFR cylinder heads.This engine retains the factory-style lifter trays but features upgraded Summit Racing hydraulic roller lifters. The camshaft is also from Summit (PN SUM-8702) with 236/246 degrees duration at .050-inch lift and .612-inch of lift on both the intake and exhaust. We installed a new set of Fel-Pro MLS (multi-layer steel) head gaskets and re-used the AFR 215-cc Mongoose cylinder heads from our prior build. These are cathedral-port-style castings that flow 312 cfm at .600-inch lift.With the heads in place, we installed the pushrods, rockers, and the timing set.With the valvetrain fully installed, the next step was to install the oil pump on the front of the engine. We used a Melling 10295 with the lightest oil-pressure spring. The LS-type oil pump must be centered around the crankshaft snout, and we followed Melling’s recommended procedure to accomplish this. First, Melling advises installing the pump finger tight; then the engine should be rotated at least one full revolution to center the pump’s rotor. Once the rotor is centered, the pump housing is torqued to 18 in-lb.After the oil pump was bolted on, we installed the pump pickup and the factory windage tray making sure to shim it with washers to clear the new, longer-stroke Summit Racing crankshaft.Known as the barbell, this fitting will keep an LS engine from building oil pressure if it is left out. It goes right behind the rear cover; we used an upgraded billet barbell from Summit Racing.Next it was time to install the rear cover. We used this alignment tool from Summit Racing to make sure the rear cover was properly centered on the crankshaft before bolting it down.The front cover also needs to be properly aligned on the crankshaft. We installed this Summit Racing SFI certified harmonic balancer and then snugged the cover in place. LS engines use steam ports to help eliminate air from the cooling system. This Summit Racing AN steam-port kit ties all four steam ports (one at each corner of the engine) together and comes pre-bent with fittings installed.We installed new O-rings into our Holley split-port intake. This engine will be carbureted for the time being.The finishing touches included polished Holley coil covers that hide MSD high-output ignition coils, and a polished Summit Racing 7-quart oil pan.On the engine dyno at Westech Performance, topped with a Holley 950-cfm Ultra XP carburetor, the engine made 600.7 horsepower and 537.5 lb-ft of torque with over 500 lb-ft on tap as early as 3,500 rpm.
