Mercury Racing has thought it was leaving some $$$ on the table because of the significant retail price gap between the 8.2L HO and the Merc Racing 525EFI. The 520 is supposed to cut about $10,000 off the price of a 525EFI and be about the same horsepower. Since it comes out of the "Racing" department, it doesn't have to have catalytic converters like the 8.2 HO to be EPA and CARB compliant. The 520 also has cast iron exhaust manifolds and risers instead of the very costly CMI stainless headers.