Lets say I am thinking about buying a old 420/425 merc and using it in a bravo application. I currently have a 330 454 with bravo 1.

From my research I will need to use my existing bellhousing, flex plate, and starter. I am fairly sure that my shift bracket will mount to the riser with a bracket and keep it in the same location. I also think my throttle cable should work with no modifications. Oil filter may have to remote mount.

What else am I over looking?


But before I did all this work above and take out a perfectly good 330hp motor what should I consider doing to the 22ish year old 420/425.

Should I replace head gaskets? Valve job?

The 420/420's are said to be low hour and run strong but I would do a compression test/leak down before install so lets assume that compression/leak down yeild good results.

Any more pointers?

You are buying an old used engine, plan on a rebuild. Keep your 330 on hand. Unless you ran and maintained the engine you do not know what you are buying. What are your goals with the 90hp increase?

Would like to run 65. Then get hooked on speed and buy a faster boat...lol

I just can't not mess with something.

If it has the stock 420 exhaust the risers leak.

What would be a faiir price for a well maintained drop in motor?

Thanks for the info so far.

flywheels are different from 330 to 420, you need a flywheel from a forged crank not cast, they are balanced differently. I went from a 330 in oulaw24 to a new 435hp 502 this year and picked up 10mph...58 to 68mph....

I am at 59 now with the 330 so 65 is real doable with 90 more hp. Just leary of a 22 yo motor. Dont want to invest 2500 to 3500 now on a pos old motor that needs 3k to 5k of rebuild work one year later.

LC