What years did Mercury produce the 500EFI? Were they a decent engine? What was the true HP?
Thanks!

1999 to 05? Maybe.

Mine bone stock dyno full wet exhuast and all ass right around 512 and 515.

They are great engines.The later serial number groups were built with Manley rods. The earlier groups had stock GM rods. Stock for stock the GM rods are fine, the Manley rod motors are nice when it comes to rebuild time. The injectors are known to be problematic with the 500efi but there is a solution for that if need be. We have had many of them on the dyno. They all make right at 500hp