Does Silent choice or switchable thru prop exhaust make a difference with potential reversion with a 500 EFI spec engine? Aluminum Gil's and Stainless risers.

Conventional wisdom would say yes, there is more potential for reversion with silent choice, but Merc has certainly approved factory setups with silent choice and that would lead us to believe its more a function of dry riser length, contingent on cam overlap of course. I would say as long as you are running the factory longer CMI tails w/ silent choice you should be fine unless you boat where there are some unusually long idle times. No way should you use the std Corsa type diverters with the overlap of the 500EFI cam

I tryed Gills with no silent choice and dry to the tip on my old boat with 500 efis and got reversion real bad. Ended up buying CMIs and no more problems.

i am pretty sure that mercury marine put out a bulletin telling boat builders NOT to send the exhaust through the out drive on the hp 500&hp500 efi engines,but a lot of them did it anyway.

I have no personal experience with them but have read plenty of people's engine sucking water when a flap malfunctions or sticks.

absolutly

I didn't know they put Gils on 500efi, could you not put the switchable CMI's on the tails

I have it on a 99 HP 500, and haven't had issues. Only use at idle around docks late at night mostly. No signs of reversion (hope I don't jinx myself). Mine has the tall late style risers on Gil's and are Corsa diverters with mufflers in tips from the factory. Which I'm told are all not good things , but at 155 hrs and it seems to be fine even after pulling the exhaust. It has turbulators installed as well.