View Full Version : 454 Mag Pistons

07-09-2009, 09:41 PM
What Pistons did Merc use in the 365 HP 454 magnum Motors?

07-09-2009, 11:06 PM
not sure what brand but i believe they are forged slugs if that helps

07-09-2009, 11:13 PM
Do you think Forged 8.5:1 Speed Pro's would be a simular replacement?

07-10-2009, 12:03 AM
If you're planning on staying stock, any forged piston will be OK. If you want to get some more easy HP out of it, you'll probably want a better piston. There are alot of differences in materials, quality, design and strength in a better piston. HOW an engine is assembled is usually more important that the parts.

07-10-2009, 12:12 AM
The boat I'm buying has 1 motor in it that has 10 hours on it. It was built 3 years ago and has no build sheet and the guy that built it doesnt remember what got put in it. I need to make a twin to it. He thinks he put a Comp 280AH cam in it and since he mentioned possibly speed pro's, I was just curious if that would be a standard replacement.

Either I'm going to build what I think it has or I'm gonna build what i want and then next year go though the other motor and make it like what I'm building this one as.

07-10-2009, 09:06 AM
Speed Pro is the old TRW catalog. OK for medium performance applications.

As long as they fit and they're forged, buy what you can get a good deal on.

07-14-2009, 03:20 PM
454 mag pistons were forged TRW's.

07-15-2009, 06:20 PM
454 mag pistons were forged TRW's.

Thanks Guys.

07-15-2009, 07:05 PM
The Speed Pro P/N for a stock forged 365 mag piston is L2399F