Gen 2 (96-02): 8.0L – 450hp, 490lb-ft
Gen 3 (03-07): 8.3L – 500hp, 525lb-ft (Gen 3 Coupe: 510hp, 535lb-ft)
An all-new body style was introduced as well as 18/19 wheels. Under the hood the bore was increased 0.8mm and the stroke lengthened 2.1mm (102.4mm x 100.6mm) to share a common rod and piston with the Hemi which returned in 2003 after a 30 year hiatus. 2004 engines went to a powdered-metal rod and changed to much better flowing CFD optimized ports, the combustion chamber was optimized, intake runners shortened for more rpm breathability, and the return of the side exhaust which had a crossover pipe known as the “ring of fire” which tuned out sound and maintained back pressure. This “ring of fire” however, made cabin very hot. I’ve always viewed the Gen 3 as the “Porsche 996” of the Viper world. While a step up and advancement over its previous generation (993), both the 996 and Gen 3 Viper lose some of the character of its predecessor and is probably the least valuable version.
Gen 4 (08-10) 8.4L – 600hp, 560lb-ft
The body was virtually unchanged from the Gen 3 to 4 other than the prominently more aggressive hood vents. The major difference is under the hood where a 100hp increase was achieved despite stricter emissions standards, which meant no longer could they use big lobes and cylinders to make power. Valve overlap had to be reduced, to the tune of 100hp (losses) for misfire detection. The Viper was the first production car to use cam-in-cam variable valve timing which was the solution not only to maintain power with stricter emissions but contributed a lot to the horsepower gain over the Gen 3. Variable valve timing Fixed intake and variable valve timing for the exhaust gained low end power and allowed the control over the exhaust note. This ability allowed for the elimination of the ring of fire crossover behind the passenger seats which greatly cooled down the passenger compartment.
The Gen 4 Viper used CNC ported heads which greatly improved airflow over the Gen 3 by creating optimized intake shapes that physically could not be cast into the head. The 8.4L of displacement was due to a communized piston with the hemi since Cast pistons made more power anyway. The Tremec T6060 replaced the T56 that was used in every previous viper. In 2010 a shorter .81 fifth gear greatly improved high-speed acceleration allowing the Viper to hit 200mph 14 seconds faster than the previous .75 gear.
Gen 5 (13-Present) 8.4L – 640hp, 600lb-ft
The Viper received a whole new design that is almost ‘Retro’ in nature with a silhouette that more resembles the Gen-2 than the Gen 3. This generation returned to forged pistons due to the overwhelming demand from Viper owners. Light weight sodium filled exhaust valves were implemented as well as a single catalytic converter (vs the dual cats used in the previous car), aluminum flywheel and a 25lb weight reduction in the engine.
A shorter 3.55 final drive (from 3.07) was implemented and the 100lb lighter chassis had a 50% increase in torsional rigidity (11,400lb/degree) over the Gen 4 mostly due to the X-brace derived from the Viper GTS-R. High strength steels and carbon fiber for the hood, roof, and rear hatch were used as well as a 12lb lighter plastic intake manifold with better thermal characteristics and evened out intake runners. The 10-12hp increase was from a cam change and 5hp from a high flow cat.
Viper Gen 1-4 Dyno
Here is an overlay of the horsepower and torque curves of the Gen I-IV Vipers measured at the crank. This is a good visual to see how over the generations, Chrysler improved the high RPM airflow and breathability of the massive V10, which results in more power. It’s impressive to see torque increases almost every year below 4,000 rpm and above, the power and torque gains just sky-rocket with every generation. While the Gen V is rated at 640hp, they are consistently putting down similar numbers to the Gen IV cars.SOURCES:
