I guess because they’re indestructible, that’s why. Unless you’re Bill Heyen of Extreme Diesel Motorsports. He’s upgrading to an SQHD this winter (shown here is a Rockwell 106). Which is sad to say, but the sled pull season is in fact winding down here. In another month the tracks will be dormant, and competitors will start to make their off-season move for more power.
Heyen’s a sled puller that competes regularly on the ITPA (Illinois Tractor Pulling Association) circuit, and is always looking to make more power—which he plans to do this winter with a different engine package—hence the upgrading of the rear axle. But, like a lot of pullers, it’s top secret for now…