Most reliable hp & torque for x15

[Brock]

525 and up is x15 performance
500 and down is x15 economy

My ISX 15 small cpl 500 is almost at 2 million km on original engine and still running strong, 4:11 gears 100,000lbs+ it's whole life.

525 and higher motors don't last as long but here's the kicker....... they usually haul more weight which is why the guys get the higher HP engine's so we're not comparing Apple's to apples.. ....