I'm about to make a move on a boat with twin 450's, I never knew there was such an engine, until I came across this boat. I have done some searching, & I couldn't find alot about this motor, other than, Merc on made it for a year or two, it is suppose to have the same internals as the 500. I didn't find anything negative about it, so I do hope that is a good thing . The motors have about 80 hours on a complete rebuild, & I understand that the "magic" hour on a 500HP is 300 before having to go thru.
So, I'm just looking for any info on this motor, what HP is it rated at, reliability, is it a solid tappet, or is it the hyd roller? Are the specs the same as the 500HP, other than the stroke?
I appreciate any input on this.

Is the seller able to produce any receipts for the rebuilds? How many hours before they were "rebuilt" I have seen a boat that got a new head gasket and valve job after an overheat that claimed a complete rebuild.

Yes, he has all recipts, & rebuilds were done with low 300 hours, now the boat is at 410 hours. From what I hear the hour for HP motors is 300, before a "refresh", but I would assume that could be sooner or later, depending on how hard those hours were....just a guess though.

sounds like its time for a survey. Have the surveyor do a leak down test on the motors, at the very least a compression test.

I'm definetly going to have a survey done, I was not aware that the surveyor would go to that depth. I figured that would be on me to do for myself.....Sounds like money well spent...thanks.

Survey is the answer. Receipts are good too. As for the 450 HP’s… They were great. They were a 500HP built on a 454 block instead of a 502. Got to check the value springs ever 150 to 200 or so. Also understand the exhaust. Dry or Wet? Crossovers or water pump. That will tell you a lot more.

Pat at AT built a 32 for a guy in St. Marteen in the Caribbean back in '96. Boat ran good and reliable..use to see it run over to Antigua and run the local races and then run back across the open Caribbean 100+ miles to St. Marteen.
Another friend of crb76 and mine installed some in an older Bullet and it would run within a couple of mph under our 32 Thunder with 502/465hp's with our dry exhaust. To this day I believe the 465's were the most wicked sounding motors. With or without dry exhaust. Dry was a must so they would last.
They hated them in Broward County either way..just ask Pat

A little off the 450's, but there's a low hour boat with the 502/465hp's that I've had my eye on. Other than sounding good, were they a pretty reliable motor? I just haven't seen many of them around. I've heard they were the precursor to the 500's.

Appreciate the info, they are definetly wet, & I see a water pump in the pics, so does that shorten the life of them?

As a matter of fact, this is a 96 Thunder that I'm intrested in. I really hope things all line up, & it works out.
It does seem that you just don't hear too many "bad" things about the HP motors. I'm looking for simplicity, & reliability......Carbs don't get much simplier (is that a word? lol)....