The Mercedes fan would cool the twin turbo 440 in 100 degree Texas heat. The turbos were just inches away from the radiator and I had hot exhaust pipes running up and down each side of the engine compartment. It could cool the engine during repeated hard pulls under boost. We beat on it for more than three hours, never going more than a few minutes without a hard run. The temps were in the 90s that night and the engine never ran hot.

The MB fan draws air from more than 95% of the radiator core. The HHR shroud is much smaller and therefore draws air from a much lower percentage of the radiator core.

I would much rather have too much fan than too little.