I was wondering if some of you could give me some insight regarding these engines.
Common problems
Recommended Service Intervals
Reliability
#hours before parts failure/ rebuild

I am looking at 2 boats and they both have 500EFI power.

Thanks in Advance

HP 500 EFI or carb are same basic animal, you can dig out a lot of info on here about them.

Basics, 200 hrs change the valve springs, spend some bucks and get quality springs, shims and retainers. Check the chit every season for signs of problems. Check the Crane roller rockers seasonaly and plan to replace around 200-250 hrs, or just change to the Crowers and forget them. Plan on changing the roller lifters around 250-300 hrs. Other than the valve train they are good motors, most all failures have been valve train related. When I had to rebuild mine it was a broken valve spring that caused it, dropped a valve, was very lucky did not do much damage other than mark the top of the piston, the internals were all fine, that was at 176 hrs. I would own them again, but would just use beter quality parts than Merc did in the valve train. A few xtra bucks will save you in the long run. Have someone do a leak down test on any you are looking at and you should be fine.

I have had several of them and had no problems.
They are very reliable.
I have a friend that has 500 hours on his and he runs them pretty much WOT all the time.
O problems for him.
Depending on the boat they are pretty good on economy and you can run 87 octane in them which is nice.
I have been very pleased with mine.

The best most reliable most race proven power plant in the marine industry.

what about borring them over 30 over? do you start to see unreliabilty with small engine working

This engine is solid platform for most modifications and depending on how wild you go will still be very reliable.

We have a kit that takes the 500 up to 620HP. Have about 6 or so boats that have been running it successfully with zero issues.

What do you do to the 500EFI to get to 620HP? Heads, cam? Cost?

i have 280 hrs on my 500 efi in my Top Gun, i would like to get them to 620 hp, Who does that work ?