Please forgive my ramblings and not sure I want to spend more dollars to up grade but would sure appreciate your input. I keep looking at the 540 EFI. Have also looked at the 565 but assuming this is like the older 525 which requires head work every 200 to 250 hours, I'm saying this isn't for me. Figuring the 540 is like a pumped up 502 and should be reliable as regular use motor.

Regardless of ci, it all depends on how aggressive the valve train is. Even the 500efis need 200-250 hr mainentance. Not sure how going to a 540 eliminates that problem?

Sounds like you are interested in an new engine, preferrabley a Mercury branded product (even though there are other good options), that is reliable, longer maintenance intervals with decent power and performance.

The Mercury/Mercruiser 8.2L Mag HO would be a better fit than the Mercury Racing 520/540/565.

https://www.mercurymarine.com/en/us/...ercruiser/82l/

The 525efi, 520, 540 and 565 are from the Merc Racing Division and all use the same cam and valve springs.
Valve train refresh every 200-300 hrs will be equal for all of them.

I’ve heard nothing but good things about the DTS (digital throttle and shift) with those motors. Any merc racing motor will require at least top end maintenance. They’re still a push rod big block, the 520 and 540 being bored to 8.6L while the 565 is stroked to 8.7L. Two year warranty is pretty awesome. I’m sure they’re another great generation of engines from mercury but you will pay for that$$$$

That being the case then guess I have something else to put on the calendar for my current motor.

Appreciate the input by all, thanks

What's your current engine, boat, and how many hours?

Have a Formula 27PC with a 509