Total Flow

Although great things were achieved with the cylinder head,it is one link in the chain of flow into and out of the engine. The flowsystem begins with the Donaldson PowerCore airbox where attention isgiven to flow efficiency and flow is increased 20 percent as compared tothe LS2. To work with the revised cylinder-head intake-portconfiguration, an all-new intake manifold was developed to meet the highairflow demands. Like the other Gen IV small-block intake, this intakeis of friction-welded, three-piece construction, produced from acomposite material. The throttle body was enlarged to 90 mm, and theinjectors were uprated to meet the demands of the engine's requirements.The exhaust system features hydroformed individual tube headers leadingto a unique inline collector flange. A sweeping collector forms atapered transition from the header flange into the wide-mouth high-flowcatalysts mounted immediately aft.

The exhaust system features hydroformed individual tube headers leadingt a unique in-line connector flange. A sweeping collector forms taperedtransitionfrom the header flange into the wdie-mouth high-flow catalystsmounted immediately aft. The exhaust system features a pipe diameter of3 inches.

The Pump

The bottom end of the engine comprisesthe short-block assembly, and the exotica found at the top of the LS7 iscontinued downstairs. The job was to accommodate the displacementincrease, and build in a level of strength and reliability suitable forhigh-rpm operation. The LS7 block is unique, partially to meet theincrease in displacement and partially to withstand the output theengine is designed to produce.

The engine block features a bore size of4.125 inches and, rather than the cast-in-place liners of the other GenIVs, receives thicker-walled pressed-in dry cylinder liners. The boresare finished with torque plates fastened to the decks to simulate thedistortion created by the cylinder-head fasteners. The main caps areinstalled and torqued during machining operations. This procedure,typical of custom-built racing engines, allows machining and finishsizing to be accomplished while the block is stressed analogous to afterfinal engine assembly. Truer tolerances in the assembled engine are theresult.

Adding to the strength of the bottom end is the use of six-boltdoweled forged-steel main caps in the place of the powdered-metalmaterial used on other Gen IVs. The main caps secure a 4.00-inch strokecrankshaft forged from 4140 chrome-moly steel, with rolled fillets wherethe journals meet the cheeks. This specification of crankshaft is moreakin to a race crankshaft than the undercut-fillet carbon-steel forgingsused in older production engines. While the high-grade steel in thecrank is notable, the real news in materials relates to the connectingrods. The use of titanium provides a uniquely high ratio of strength andfatigue life to weight. Titanium is exotic even in the racing world, andits use here is a first for a domestic auto manufacturer.

Other aspectsof the LS7 engine borrow from principles having more in common with theracetrack than production automobiles. The lubrication system of the LS7is unique, as it's a variation of the dry-sump arrangement normally seenonly on the racetrack. Rather than supplying oil from the bottom-mountedsump directly into the engine's pressure-fed lubrication system, the LS7employs a two-stage oil pump and reservoir tank. The scavenge stage ofthe pump continually evacuates the engine's lubricant, sending it to theremote reservoir tank. The tank allows high capacity without the penaltyof windage losses, aeration, and control difficulty associated with oilcollection in a conventional sump. The oil accumulates at the reservoirtank and is drawn back to the pressure stage of the system, providinguninterrupted and reliable pressurized oil under the most demandingdriving conditions.

Compression ratio has been moved up to 11:1, seriousterritory for a pump-gas powerplant, made possible through advancedengine management and the fast-burn technology built into thecylinder-head design. The pistons are full floating and are designedwith the pin supports moved in. This allows for a shorter pin, which isstiffer and reduces reciprocating weight. The piston ring lands areanodized for improved surface hardness and wear resistance, while theskirt portion is coated with a lubricious polymer to reduce borefriction.

You might notice the recurring themes of strength and weightreduction, and this isn't coincidental. Lighter-weight components induceless internal engine stress, which is exponentially increased with rpm.Larger displacement through longer strokes increases piston speed, andthese factors conspire to place a demanding load on a voluminoushigh-rpm engine. Reducing weight reduces component stresses. Figuringout how that can be accomplished while adding strength is a credit tothe engineers on the program, and the goal of any racing engine builder.