On a side note I have a line on an entire cam/valvetrain from a very low hour 425 HP 496 Mag Mercruiser for $300 that was given the Raylar treatment. Cam/Lifters/Pushrods/Guides/Studs/Rockers and double roller timing set. The cam and matching tune is worth 50 HP in the 375 HP Marine version of the 8.1 making it the 425 HP HO. I am sure the rest of the gain over the 340 HP truck version is exhaust/intake/tune/loss of the mechanical fan. The cam does its thing under 5,000 rpm as well and has a nice sounding idle.