I need to freshen or replace two 2000 502 MPI's, and I am afraid my blocks are severely corroded. With the age of the internet, there are many companies selling new longblocks, rebuilt longblocks, remanufactured, etc. Hard to decide what is good or bad.

Even with the new longblocks, how do you know what you are buying? For instance, isn't there a difference between the carburated longblock and the EFI longblock (camshaft)? I am not seeing companies make a distinction between the two.

How about remanufactured? Why would Mercruiser sell a remanufactured 502 longblock for $7500, when you can buy a
supposidly NEW GM longblock for $5300. Is the Mercruiser better?

It depends on who is building them. It's been severaly years since I went down this road. There are several threads on this issue search the forum.
There's a lot of truth in you get what you pay for.

Has anyone tried the Mercruiser Remans?

MY 502 was built in 93 from merc it was a 390hp. it's been rebuilt 3 times once at 585hp, 595 hp and now its a 510 647hp with a 850 and with the new nickerson 1050 its 670hp there was a 13 to 20hp diffence from the old 850 under jetted. my block is fine. I would just give your motors to a OSO ENGINE BUILDER AND HAVE IT DONE RIGHT. I hEARD SOME HORROR STORYS JUST LOOK AT WHAT HAPPENED TO DEAN he got screwed from ENGINE WORLD WHO ALL SO GOES UNDER SOME OTHER NAMES i DO NOT HAVE THE LIST ON ME ITS LIKE 430AM . iF YOU WANT i WILL FIND THE THREAD SO YOU CAN READ IT ART

I know what you mean, there are alot of builders out there. But do you think the 502 rebuilds straight from Mercruiser with up to a three year warranty are worth the extra money over a supposedly new GM longblock?

Yes! I have also found out the hard way why Merc engines cost so much.............they are worth it! On one of my boats, I'm on the third engine, with no more than 15 hours in three years from dcking around with shadetree mechanics. That is assuming you're not trying to make BIG hp, then there are only a handful of builders I would trust.

The Merc reman engines are good quality rebuild. They use decent parts and build them OK. The last couple I've seen actually had Dart heads on them...Going with new GM stuff is fine, but I'd have a competent shop disassemble the short blocks and set the piston to wall clearance correctly along with checking bearing clearances. I've done a couple and found them pretty tight. Probably would have failed if run as shipped. But the cost savings over Merc would still be worth it and you would have new parts. You can then go back with the correct gaskets and cam.

Hmmmm , lets see , merc will pay your labor if your engine fails and sounds like there is a guy inside with a hammer saying let me out. Will the dealer that sold you that gm "marine" long block , I know not!

I could rebuild them cheaper than a new longblock

Now there is a great Idea! You'll be sure it's done right!