First Test: 2008 Dodge Viper SRT-10
Preemptive strike: With a 600-plus-horse Corvette on the horizon, Dodge pits for more Viper venom
By Frank Markus
Car-company intelligence is way more reliable than that of our national government, so the Deciders at Dodge have known with absolute certainty that the Bow-Tie Boys have been hard at work on a whopper of a WMD for a couple years. So they're launching a preemptive strike with their own Weapon of Mass Displacement -- a significantly revised V-10 packing a nice round 600 horses and 560 pound-feet of torque, and all of 'em SAE certified. So where'd they find an extra 90 horsepower and 25-pound-feet? In the three places all racers know to look:
More Displacement
An extra millimeter of bore (to 103 mm) boosts capacity from 8.3 to 8.4 liters Pistons and rods borrowed from the 6.1-liter SRT-8 Hemi V-8s boost compression ratio from 9.6:1 to 10.2:1Iron liners are pressed into a block with improved water jackets for more efficient cooling
Better Breathing
Lower-restriction air cleaner routes the intake charge through twin electronic throttle bodies (cribbed from the new 4.7L V-8)Two-piece crossflow intake manifold and plenum features smoother runnersIntake and exhaust valves are larger, thanks in part to new offset-exhaust-valve rocker armsCylinder heads feature combustion chambers and intake-runners now computer-machined for smoother airflow, with fuel injectors mounted closer to the intake valvesExhaust-valve timing can vary overlap continuously within a 40-degree range-a world's first innovation for cam-in-block engines.Sidepipe exhaust system flows 20 percent more efficiently (also weighs less, as there's no crossover pipe).
Higher Revving
Hollow-stem intake valves lower weightInvestment-cast intake rockers further reduce valvetrain inertiaPistons get larger-diameter wrist pins and bronze bushingsPowdered-metal connecting rods use aircraft-quality fasteners for increased fatigue strengthCross-bolted main-bearing caps improve strength and durabilityA larger oil pump with a swinging pickup (adapted from the Viper Competition Coupe) improves oil pressure under high-rpm and high-g operating conditions.
CamInCam-in-Block
Dodge and the SRT gang have managed the seemingly impossible -- variable exhaust-valve timing in a single-cam engine. The system is trademarked CamInCam, which aptly describes how it works. The assembled cam consists of a tube onto which the four double-lobe intake cams are press-fit. In between them, the exhaust cams are pinned, through slots in the main tube, to a second concentric rod. An off-the-shelf hydraulic cam phaser from INA can rotate this inner rod by up to 45 degrees relative to the intake-cam tube, but the Viper is currently only utilizing 40 degrees of that range. Minimal valve overlap makes for smooth, quiet idle and clean emissions, while big overlap boosts power when the hammer's down. Between idle and 3000 rpm, depending on throttle position, the overlap increases to the maximum amount. The system is less expensive than two or four cam phasers on a DOHC engine, so expect to see this technology spread among other high-end OHV engines.
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