I have an unknown engine that came partially disassembled in a 271 fastech I bought. All that was left was the short block with seawater pump, crank pulley, circulation pump (all mercury racing blue) and a blower pulley (black) on the blue crank pulley. Those two locked together and had one set of bolts going through both.
Also has fuel management system from Aeromotive on the bottom of the motor, braided stainless for fuel and oil lines. and a vortech engineering oil line from the back of the block.
So at first I thought maybe a 500efi with a vortech supercharger?
Then I find the 496 bell housing (which formula confirmed it came with) and figured he just put the pretty pulleys on for show.

Pulled the engine tonight and took it apart and found this:
Block 8.2l stamped 10237300 and K30 on both sides MK9 behind flywheel.
Pistons: JE 755D Large single depression covering most of piston.
Rods: Eagle H-beam stamped M1 09 and another changing #
Arp rod bolts

So now I'm thinking 575sci ???

Is there a mercruiser serial number identification plate riveted too the engine block next to the strarter area?

If so, what is the number? This will be one way to tell what the engine was.

Probably had a custom 502 SC'd engine and used some the 496 parts that fit.

Boat tech: no mercruiser plate anywhere.
Griff: I was starting to think that too, but the factory mercury racing pulleys has me thrown off. I know you can buy them....but why $$$

It could have started life out as a 500efi or 575sci.
The Aeromotive stuff would show that something else was done and it wasn't stock.

If someone can help me find out what engine I have,the serial number is 3915983

Is this a MERCURY outboard engine?

a mess...time to start over