The iconic hand-assembled 8.4-liter all-aluminum V-10 engine continued, upgraded again with improvements in oiling, airflow and an industry-first single-cam variable-valve timing system, boosting power to 640 hp at 6,150 rpm and 600 lb-ft at 4,950 rpm.
For 2013, the engine had a new high-flow, composite intake manifold, new forged pistons, new lightweight, sodium-cooled exhaust valves, and an aluminum flywheel, as well as new catalysts to reduce back pressure. Sodium is added to the exhaust valve stem for better heat transfer and helps prevent hot spots in the valve head and combustion chamber that can lead to engine knock.
The result is an improvement of 40 lb.-ft. of torque and 40 horsepower, with weight savings of more than 25 pounds for the fully dressed engine.
The Tremec TR6060 six-speed transmission has been refined with tighter gear ratios and a shorter-throw (by 12%) shifter. The final -drive ratio has been shortened to 3.55 from 3.07, giving the 2013 SRT Viper even more voracious and effortless acceleration at all speeds. The sixth gear provides more power at the higher rpm ranges of the engine (Ralph Gilles said they can now be used more often, rather than only in highway cruising; and the car now achieves top speed in 6th rather than, as before, in 5th). The leather-wrapped shifter assembly is connected directly into the transmission to eliminate levers and pivots. The result is a direct-mount shift system that provides a solid and precise shift feel.
The 90-degree, deep skirt block uses high-strength cast T356 aluminum and includes cast-iron bore liners, strengthened bulkheads for block rigidity, and improved water jackets for consistent temperatures across the engine. The bore and stroke of the cylinders are 103 mm by 100.6 mm (respectively); compression is 10.2:1.
The forged-steel crankshaft is supported by six main journals with cross-bolted, four-bolt, main-bearing caps, two vertical and two horizontal. Forged, powder -metal connecting rods measure 158.6 mm. Forged aluminum pistons are 10 g lighter than the prior design, and designed for lower friction; reduced diameter, full-floating 24 mm piston pins are new. New steel piston rings also reduce friction with a 1.5 mm top and a 1.2 mm second ring width.
The aluminum flywheel reduced weight by 11 pounds, and includes a steel outer-ring gear and friction wear surface for durability. When combined with a twin plate 240 mm twin-disc clutch, the flywheel cuts overall rotating inertia by 20%, good for roughly 1/10th of a second reduction in 0-to-60 acceleration and better performance in lap times on a typical road course by approximately 0.5 seconds. (Together, the composite intake and revised block cut 17 lb.)
For improved cooling, particularly at the rear cylinders, the head gaskets have been redesigned through the use of computer simulations, validation and extensive testing to provide more balanced cooling across all cylinders.
With optimized coolant flow, a more balanced cylinder-to-cylinder temperature distribution allows for improved performance.
The 8.4-liter V-10 cast-aluminum oil pan is fitted with special baffles, channels, and scrapers to funnel engine oil back into the sump, and serves as a structural component to reduce powertrain bending.
A unique, race-proven swinging arm oil pickup moves with relationship to G-forces encountered in tight-track turning conditions, acceleration and braking conditions. Exclusive to the Viper, the swinging pickup moves within the oil pan to ensure that the maximum amount of oil is available to the engine without any losses due to side-to-side sloshing in the pan.
A single gerotor oil pump provides the pressure for the oiling system and is directly driven off the crankshaft. The engine oil cooler is standard.
Oil change intervals are recommended at 6,000 miles, using Pennzoil 0W40 synthetic motor oil only. The crankcase capacity with filter change is 10.5 quarts. A special SRT-designed oil filter is needed.
The intake assembly is new, using a lightweight composite intake manifold for better fuel/air distribution, excellent thermal capabilities, and reduced weight. Its runners are around one inch longer, and the move to composite from aluminum reduced air charge temperatures significantly.
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