so last year I pulled my engine out to do a freshen up and came to the conclusion I would not be re boring the block due to corrosion and age. I than went ahead buying a brand New GM Block newest version (I believe Gen V1). the rebuild turned into almost a new build, we used new pistons, cam, roller rockers, lifters, intake, oil pump, timing chain , completely rebuilt original cast heads with new springs and valves etc, rebuilt carb... basically everything except crank and connecting rods. We built the motor to mirror the stock HP 500 merc with OEM parts, mostly since I was looking for reliability... I wanted the same motor package as I had before.

close to the end of the season I noticed I was slightly down on power ( maybe 25 hours max on new motor) and we found that I had reversion problem with some rusty valves and cylinder walls/rings, the exhaust and tails were new and pressure checked and not the cause of the problem. Fast forward this winter I have the motor at the machine shop totally apart for machine work and to put it back together. I plan on going with dry exhaust since reversion seems to be the only culprit. My question to the motor gurus out there would you put this motor back together with the stock OEM mercury racing cam that came with the HP500?

Do you have silent choice? Could the reversion be caused due to bad flappers?

I just hate putting engines back together stock so I'd bump the cam a little to the 741 provided your springs are ok with seat and open pressure. I would think they would but something to consider anyway. Just how much HP gain I'm not certain but I'd guess 25-30. Same cam in 525 hp efi I believe. Maybe some others have done the same thing am can chime in.

no silent choice , flappers were good,

[QUOTE=getrdunn;4526808]I just hate putting engines back together stock so I'd bump the cam a little to the 741 provided your springs are ok with seat and open pressure. I would think they would but something to consider anyway. Just how much HP gain I'm not certain but I'd guess 25

good point not sure if the 525 cam is direct swap , the 525 efi cam may have or may not have a gear for oil pump...not sure im explaining correctly but I remember hearing something along those lines, curious to hear more people chime in

HP 500 carb or efi? From what I understand the pre efi units were 110lsa while the efi units 114lsa

my motor is Carb NOT EFI

The 525 EFI cam has the distributor gear and is a 114 lsa, the 741 is same lift and duration on a 112 split according to Crane

110lsa then, as far as I know. "Almost" guaranteed reversion if that's the case depending on exhaust, valve timing, etc. I don't know why you got away with it on the first motor.

does that mean it will swap directly, does my HP500 have the gear as well?