Volume III, Issue 6, Page 27

The bowls are done in both castings but the chambers and runners are still untouched. HPS retains the original runner finish except around both sets of valves, which get knife-edged. HPS lays over the short turn radius (measured from the deck surface to the radius) to get more volume into the runner.


Prepping dime-a-dozen LM7 (5.3L) cylinder head for turbocharging

When you figure that GM built its millionth LS engine a year ago, and know that way more than half those jobs went into pick-up trucks and SUVS, it’s a good indicator of good goods at a reasonable, if not give-away price. The heads in this discussion are from an LM7 5.3L Silverado, but they could just as well have been from an LY9, LMG, LH6 or LC9. Strange people, those GM folk. The RPO engine number depends on the vehicle it is destined to power.  

HPS (Cylinder Head and Manifold Development) owner Matt Hilton has been porting heads for 18 years, guided by a natural talent and taught by the right profs, guys he was intuitive enough to establish himself with early on. Matt also did field stints repairing grove-pump engines, then matriculating to big Cats and Detroit Diesels. He’s also a great wheeler-dealer. On top of that he loves what he does and claims a constant flow of paying jobs. HPS’ ace porter and flow-bench pilot Chevelle Rob Cossack ran the numbers on Chad Brady's porting work and interpretation.

The engine these heads are going on has a displacement of 364 cubic inches and is destined for a 3,500-pound ’80 Malibu. In that the car is licensed and insured, we’re calling it a street and strip arrangement--with a serious night-cat attitude. The LS1 block holds some good 4340 stuff from Eagle (crank and rods), Wiseco 9.0:1 forgings teamed with Hellfire rings. Single 88mm turbocharger will be aftercooled via hot air-to-liquid and blown through a FAST 92mm throttle body to the issue of 150lb-/hr injectors. Meaney’s Big Stuff stuff will be telling the engine what to do and when to do it.

Experience has proven that even the lowliest LS block will absorb more than you can put to it in a lifetime: way in excess of 700 pulls, including every power adder save for a turbocharger. The oil pan had never been off the stock crate motor, nodular crank, powdered rods, cast pistons, they all took the abuse until a cylinder wall left of its own accord (or was that in an Accord?). If you’ll feel better with iron underneath, start with a 6.0L truck block. Lot of them around, too.  

Before the initial flow tests, Matt brings the 45-degree seat angle to 35 degrees. For the best low-lift flow, he prefers Ferrea valves and machines them from 2.00-inch to 1.890-inch to fit the combustion chamber of the LM7 head (61cc). The exhaust valves are stock 1.55-inch. Max flow on the intake side was 244.9cfm; the exhausts pulled 194.7cfm. The idea was to see how much could be accomplished with the stock valve size, but bigger things are inevitable, like an1.94-inch diameter intake valve . Look where the best flow occurs and the entire string of events (before and after) the porting was done.

In the exhaust ports (left), Matt moved the wall on the pushrod side over by 0.100-inch, relieved core-shift material, and put a knife edge on the valve guide boss.

Brady widened the exhaust ports 0.030-inch per side and raised the ceilings 0.050-inch.