View Full Version : Gen V 454 to Gen VI 502

07-22-2014, 08:53 PM
We purchased our 1995 Donzi 22C July of last year and have been having a blast with it. Went through all the “seat” time everyone talks about. Had the boat over on its gunwale in a turn. Yes, it scared the dickens out of me. At WOT the engine, a 454 385HP, turned 5050rpm and hit 68MPH on GPS. This past July 4th idled out of the marina just fine. Started to bring her up on plane when the engine let go with a “Bang”:shocking:. Immediately brought it down to idle, turned around and went back in. Had the family on board and did NOT want to call for a tow as the channel was busy with fast traffic. What the yard found was a broken rocker, two bend push rods and a cracked head. Seems as though the head had been cracked for a while as there was evidence of water in the cylinder. “Keepers” for two valves were in bits and pieces. One valve bent. So decision time. Rebuild the 454, procure a new Long Block 454 385HP or a new Long Block 502 435HP. I decided on the 502. I have been searching this forum ever since for all the info I could find on the 502. Think I want to go with a bigger oil cooler and also install an oil temp gauge. I have been told that most everything from the Mercruiser 454 will bolt right up with the 502. The boat came with stainless headers and was told no problem with re-using them. I also need a new prop. Had actually discussed a Turbo prop with Chris at PP for the 454 on July 2. I have scrubbed the engine compartment and I am looking forward to doing some wiring, duel batteries, now made a whole lot easier with the engine out. So, what do you guys think, am I on the right track? Issues I should be aware of?

07-24-2014, 02:05 PM
Sounds like you are headed in the right direction! You will need a little more pitch on your prop, get it running for a bit of testing.