The Chevy Small Block LSX Engine - This Thing's Loud! Plan B

A 1.9hp-Per-Cubic-Inch LSX Lesson

Ro McGonegal Jul 1, 2009 0 Comment(s)
0907chp_01_z Chevy_small_block_lsx_engine Performance_engine 2/19

What happens when GM Performance Parts teams up with a loyal, experienced doorslammer racer to prove the mettle of its new LSX protg? More than anything it becomes a lesson learned, a lesson that can be passed on to LSX aspirants as gospel. in this case, Robin Lawrence's Nova runs the NMCA Nostalgia Pro Street class.

This current 440.180ci version arrives at its displacement via a 4.185-inch bore and a 4.00-inch stroke. Previous experiments were conducted with a 454-inch LSX equipped with much-modified C5R castings (complete with welded-on tabs at the bottom of the heads). Now it seems as if they were a stop-gap measure that proved inappropriate for the combination and seriously reduced the swept area, requiring massive work on the piston domes to overcome.

The C5R heads were used simply because no other GMPP parts were capable of supporting the power and torque levels Lawrence sought (900 hp normally aspirated). Though he could have gone to the aftermarket for the heads he needed, the edict was to use GMPP castings, period. Those pieces are now readily available, and the new engine has a completely different combination. The only items carried over from the 454 to the 440-inch version were the Dailey Oil Pump dry sump system, Stef's pan, MSD ignition, roller lifters, springs, retainers, keepers, and head studs.

Of much more importance is the stuff that got changed and why. Up first, the valve lifters were allowing oil to pass above the camshaft oil galley because the base circle on the original 55mm camshaft was too small to get lobe lift. Hence, the lifter bodies dropped below the oil galley. Changing to the 60mm camshaft required a block with a raised cam bore (0.078-inch) and lifter bores (offset drilled) that would accommodate 0.941-inch tie-bar rollers, and a custom Lunati grind (282/304 degrees duration, 0.970-inch lift at the valve, and 114-degree lobe separation). This stick was designed by Harold Berkshire with a tighter lobe separation as well as a smaller duration on the intake lobe. He increased lobe lift by about 0.005 inch. A (standard) 9.26-inch-deck LSX engineering block was machined (any CNC-equipped shop can do this) to accept the larger diameter camshaft.

A Lunati 4.00-inch stroke forging is teamed with 6.062-inch GRP aluminum connecting rods fitted with 2.100-inch bearings, rather than the 1.88-inch bearings used previously. Trend wristpins hold the 14:1 Diamond pistons that are circled by Hellfire ring packs (1/16-inch top). For a little more squeeze on the lower end, Lawrence increased the main stud diameter from 10 to 11 mm.

At this point, GMPP requested that Lawrence work with one of its developmental partners, Thomson Automotive in Redford, Michigan. Brian Thomson and his guys have extensive experience with LS engines and felt that they could extract important information from his experimentation by bringing the program to someone local to the GMPP engineers.

High-horsepower lessons (930 on nuts) learned with the 454: The 41/8-inch stroke crankshaft was flexing at high RPM. Lawrence consulted with many crankshaft experts and got different suggestions from each. Some suggested a center counterweight. Another felt that extra bearing clearance would help. In the final analysis, he reduced the stroke of the crankshaft. With the original combination, because of the bore spacing on a small-block, the area from the main journal to the rod journal is small. As you increase the stroke or the distance, you have less material. Lawrence felt that a 2.100-inch rod journal as well as a 4-inch stroke would increase rigidity.




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