How does this combo's power results compare to stock Mercury HP500EFI's ?....I might go this route when the time comes for my 502 mags.

To the top I would like to know also how it is to a hp 500

The 500EFI makes more torque in the midrange and a bit more up top too. It's got a better intake.

you did a valve job i take it? i take it ya ditched the valve seals and installed PC's?
did ya bump compression any?
did you just bolt the cam in?
did you play with cam timing on the dyno? what exhaust lift you end up measuring?
i would have expected a bit more on top even with out extending the rev limit.
I played around a bunch when this engine first came out.

Yes, it had a valve job. The cam was just bolted in straight up. This wasn't a max effort build, it was designed for it's application which was a single engine heavy sport cruiser. It idles at 625rpm in gear. The dyno test was on 87 octane, with all accessories connected, wet exhaust with two 90's, and mufflers. If I wanted to do a glory pull I could have ditched the mufflers, ditched the 90's, put in 89 octane and bumped the timing. It would have made closer to 525hp in that configuration. Or I could run dyno headers like a lot of guys do and make even more. The boat picked up 5-6 mph over the 496HO that was in it before.

perfect for the application! thanks for the reply.
i did all kinds of tinkering with those engines back then...some worked well; others not that great of a return for the money or effort.
Have a great weekend

The boat's named HellFire and it's the tender to an old wooden yacht named Heaven. The owner's probably 70ish and drives it everywhere. A four hour trip is nothing for him. He says he wants to burn as much fuel as he possibly can before he dies. He's a real character. The boat's always full of empty Corona and Vodka bottles..

NICE! Great name(s); HELLFIRE....


ps....very cool tender

Haxby--- You didn't show the whole dyno sheet, but I was wondering if there was any manifold vacuum readings on it. I'm in the process of manufacturing larger Throttle Bodies for these engines.

bump