The 3.5 L (3,498 cc) VQ35DE is used in many modern Nissan vehicles. Bore and stroke are 95.5 mm × 81.4 mm (3.76 in × 3.20 in). It uses a similar block design as the VQ30DE, but adds variable valve timing (CVTCS). It produces from 231 to 304 PS (170 to 224 kW; 228 to 300 hp) of power and 246 to 274 lb⋅ft (334 to 371 N⋅m) of torque depending on the application.
The VQ35DE is built in Iwaki and Decherd, TN. It was on the Ward's 10 Best Engines list from 2002 through to 2007 and again in 2016. It features forged steel connecting rods, a microfinished one-piece forged crankshaft, and Nissan's nylon intake manifold technology. It has low-friction molybdenum-coated pistons and the intake is a high-flow tuned induction system. Since its inception Nissan has improved upon the VQ35DE with changes keeping it an efficient class leading V6 engine.
A modified version of the VQ35DE, called the S1, is produced by Nismo (Nissan's motorsports and performance division) for the Fairlady Z S-Tune GT. It produces 300 PS (221 kW; 296 hp) at 7,200 rpm, a higher rev-limit than that of the original VQ35DE.
The QR25DE is a 2.5 L (2,488 cc) variant built with cast steel connecting rods, a steel timing chain, counter-rotating balance shafts, and an aluminum intake manifold. The engine bore and stroke is 89 mm × 100 mm (3.50 in × 3.94 in) and a compression ratio ranging from 9.5:1 to 10.5:1 depending on the vehicle. Output is rated 175 hp (130 kW; 177 PS) at 6000 rpm with 244 N⋅m (180 lb⋅ft) of torque at 4000 rpm in the Altima 2.5 and Sentra SE-R models. Altimas that are PZEV compliant create 170 hp (127 kW; 172 PS) and 175 lb⋅ft (237 N⋅m) of torque. In the 2005+ Nissan Frontier the QR25DE generates 152 hp (113 kW; 154 PS) and 171 lb⋅ft (232 N⋅m) of torque.
The QR25DER is similar to the QR25DE but has a supercharger for increased power and is coupled with a 15 kW (20 hp) electric motor, Dual Clutch System, and lithium-ion battery for increased fuel efficiency. The engine has a compression ratio of 9.1:1 and produces a combined 250 hp (186 kW; 253 PS) at 5600 rpm and 243 lb⋅ft (329 N⋅m) at 3600 rpm.
If the engine properly maintained with regular oil changes, the timing chain and tensioner should last for the life of the car -- the chain is made of steel alloy. The most common cause of timing chain stretch is lack of maintenance and regular oil changes. Bad oil can also damage the tensioner which makes the possibility of the engine skipping time or a catastrophic failure greater.
Warning symptoms of a bad or failing timing chain or tensioner are:
Engine may stall or run rough.
Noise in the front of the engine (a rattle or rumble, associated with engine speed)
Check Engine Light may illuminate and set misfire, camshaft sensor, and crankshaft sensor codes.
Sorry just re-read you post. If you are referring to the accessory serpentine belt, they typically last around 70,000 to 100,000 miles, or until they show signs of wear. A new serpentine belt has a soft felt-like surface on the ribbed side. As the belt wears out, the belt rubber hardens, cracks, and frays. If you belt has cracks in the ribs, replace it. See this video