its not a wise decision to make a 50efi into a 540 especially if your motors are low hours fresh and can be sold for considerable amounts. one would think that the trade off would cost them a reasonable amount, but done correctly with top of the line parts in the 540's you could end up breaking even. i would expect close to 700HP all day.

depends on what you want and are willing to spend. couple diff things come to mind depending on where you wnat to be power wise. i you want to be in the 600-650 range that is pretty easy with heads, cam, throttle body, injectors and programming. Also some 500 efis had the good rods and some didnt, later ones did.

Now, i just found out that the throttle body from a 525 is bigger than the one from arizona speed. check with Ron potter as he has some 500's that are 775 from a 540 block.

The thing to reember is HP costs money, how much can you afford.

btw my 500's are 625 and 670 tq with afr heads 509 CI and all the work i mentioned above.

+1 with Griff

I spoke with my engine guy and after going throught the numbers we agree I can sell the 500's and for the price of the new block would probably end up money ahead verses upgrading the stock hp 500. The one twist he threw in was his cost of block, crank, pistons, rods and all that he will need is the same for 572's as it is for 540's. He suggested the tall blocks for a mildly built easy 650-675 hp. Near as I can tell the worst part would be moving the exhaust up .5" on transom (tall block) however if I sell 500's with headers I can have tails built .5" lower to exit existing holes with new headers.
Any experiences with 572's? I am thinking have him put together 572 short blocks then Bob (Marine kinetics) cam and a couple sets of AFR's.

Ok, here is the million dollar question....I know the engines are only worth what someone is willing to pay but what can I expect to get for 2 complete 2004 hp 500 efi with 170 hours, with and without headers?

Define "170 hours". Since new (2004) or rebuilt?
The amount sold for will also depend upon the quality of the rebuild. Machine work, parts and who performed it.

170 original hours. The person I bought it from ran it on a fairly small lake so it didn't see much wot time.

I would sell the lower end complete, regardless. The price you'll get for the used crank, rods, heads and pistons won't be all that much (and you don't have to disassemble it).

You can sell your motor, less injection even, for a decent amount. IMO it will be much more than what you could have sold your crank, rods pistons and heads for, less what you pay for your new rotating assembly and block.

Remember, right now your motor has the Merc built label on it, along with work that went into its assembly, not to mention piece of mind for the buyer that's its been removed properly and still in balance. Once you take it apart, all of that goes away.

I would guess $4,500 each. I could be off, but that's a good starting point for arguments sake!

I would be interested in the 500 s .