|
She's So Great, My 408!
Nearly 600hp from a normally aspirated iron-block LQ9
Story by: Ro McGonegal
Photos by: Nick D'Agostino
The argument between the traditional small-block and the relatively new Gen-III engine (in production for 10 years) used to be based on price, availability, and aftermarket accessibility. The small-block undoubtedly had the edge. But examples of the new engine now number in the millions and simply put, it features important design changes that render the small-block antiquated by comparison. Think flathead versus overhead valve.
Salient features include cylinder heads with a 12-degree valve angle, the choice of iron or aluminum cylinder case, factory EFI or aftermarket carburetion, and much greater ease of maintenance. Further, the OEM bottom (nodular iron crankshaft, powered metal connecting rods, and cast pistons) is extremely durable, able to absorb heinous bouts of nitrous oxide as well as elevated positive manifold pressure. In normally aspirated operation, they present a very hard case. With little more than a sprightly camshaft and bountiful cylinder heads, more than 500 horsepower and 500 pound-feet of torque at the flywheel are easily manufactured by a 5.7L LS1.
Though the internals in this particular build-up are top notch and therefore command top dollar, there’s no reason why you couldn’t realize the same results with components from another manufacturer that cost less but yield the same advantage.
The Object
Though truck block material has since given way to aluminum in every application, the early 6.0L versions were equipped with the LQ4 and LQ9 iron block. This cylinder case can be safely bored to 4.030-inch and combined with a 4.00-inch stroke LS1-type crankshaft tops out at 408ci. Compared to the latest 6.0L block, the iron version weighs about 100 pounds more. For most applications, the power gained in the larger displacement outweighs this difference. The positives are the larger displacement and in the inherent strength of the iron, probably the better choice for high-boost versions. Further, the bottoms of the iron block cylinders need no clearance notches for the stroker crank counterweights; the aluminum ones do because their sleeves protrude just far enough into the sweep of the crankshaft to require grinding (see photo).
| |
