Up top, the engine features a set of GM’s factory big-port L92 cylinder heads. These cylinder heads are right on target to feed a deep-breathing stroker, with plenty of port volume, and substantial intake port flow, even in stock form. Andy tells us the stock ports flow in the range of 330 cfm as delivered, and have the potential for even more with minor modifications. If the heads have a weakness, it is in exhaust flow. Andy says, “On average these heads will flow 190-200 on the exhaust, so the intake to exhaust flow percentages are pretty lopsided.” Once reworked with an emphasis on bringing up the exhaust flow, and breathing though a combination of Ferrea 2.165-inch intake valves and Liberty 1.600-inch exhaust valves, the factory castings delivered 335 cfm on the intake side and 255 cfm on the exhaust at .600-inch lift. High-lift flow like that is power waiting to be had, but what makes it even better is strong airflow right from the bottom of the lift curve. Here D&A worked their magic with a proprietary valve job using seat and valve angles developed from their circle track engine development experience to maximize the flow curve.

To tap into the airflow of the heads, the camshaft plays a vital role in building a combination that works. Here D&A went with a custom grind from Steve Demos Cams, in Jefferson, Georgia. The resulting hydraulic roller stick features quite conservative numbers in terms of duration, spec’d at 224/228 degrees at .050, with 276/282 degrees of gross duration. While the duration is short, the lift is significant, measuring .607 inch at the valve via a set of Harland Sharp 1.8:1 rocker arms. The short-duration/high-lift combination helps to maximize torque over a broad power range, and ensures plenty of torque down low. The cam was ground on a lobe separation angle of 108 degrees, and installed at 102, or 6 degrees advanced, specifications that also favor strong torque production. The healthy torque numbers showing low in the rpm range add credence to the theory. The ample top end power right up to 6,500 rpm points out that with free-breathing heads it doesn’t take a huge amount of duration to turn the revs.

A potential pitfall when considering a short duration/high-lift cam—especially with a hydraulic roller—is maintaining valvetrain stability with the aggressive cam action. If the valvetrain can’t keep up, power production is over. To ensure valvetrain performance, D&A used a GM hydraulic roller lifter from the Cadillac CTS-V road race program. These lifters are a direct replacement for stock, using the OEM lifter guides. The rest of the valvetrain consists of COMP 5/16-inch pushrods, the aforementioned Harland Sharp 1.8:1 rocker arms, and Lunati Gold Series springs, PN 73925K2LUN. Andy tells us: “We used the Lunati Gold Series; it’s a dual valvespring and it works really well. It isn’t expensive either, and is really lightweight.”

Carbureted Combination

While the LQ4—like all LS-based engines—uses a complicated engine management system and EFI in OEM installations, for general-purpose hot rod use there are simpler alternatives. To handle the induction, the EFI was shelved in favor of a GMPP two-plane intake manifold topped with a D&A-modified Holley 750HP carb. The attraction here is that the fuel system requires no wiring or programming to make it work; just plumb it up and it’s done. Andy was impressed with the manifold: “It’s a really nice piece. There is plenty of room to port on it if need be. I didn’t do any port work on it, and it made for a really nice broad torque curve.”

The short-duration/high-lift combination helps to maximize torque over a broad power range…