I am going to be pulling my 525 EFI'S soon to do the top ends. I will also be repairing one of my heads that is pitted on the exhaust port and no longer seals. My questions are is there any more that I can get out of my heads and just put them back on the motors, or do I just repair the bad one and respring them and keep it all stock. OR I am also thinking about taking them to 540's while they are out and is there anything more I can do to the heads to help out with this build or is buying a different set of heads going to be better. It is not an open ended check book on the build but I do not want be wasteful on the build as I will be keeping this boat for several more years. I am wanting to keep it a good build that will last for a long time, not pull and rebuild every year. The boat is a 2006 35' fountain with 300 hrs and the motors have not been touched yet.

If they were mine I would not touch the shortblocks at 300 hours. You don't need a 540ci setup to make good power. Upgrading the heads is my vote. AFR or DART with more compression and better flow. Keep the 525 cam. I would also replace rockers, lifters etc....

If you do something other than stock, you should figure out who will be able to reprogram the PCM's. Only a few people can do it.
Probably best off to duplicate somebody else's upgrades who has had their PCM reprogrammed with a dyno and real world tested tune.

fuel system checks and possible replacements and or upgrades. Also have your Fuel Injectors checked out into the mix as well if you are keeping them with build upgrades - I do not know your plans with them. You can ask up here who can perform that end and Im sure my name would be in the mix for that end.

The Promaxx heads seem to be a really good bolt on head that would pair well with that cam. ADK61 (?) should be along here to elaborate.

Sorry for the curve ball change here --- just asking since you brought up about Pro Maxx heads if there is any good real world info to read and look at ? Wanted to add and not making a statement - I am not looking for comments from non users nor non dyno testing number opinions in the mix. I am not pointing my figure either at you with my statements. I like the facts and experience end for info to be had. THANKS

Okay, stock is near 560 on most dyno's. Best you'll get with killer heads and etc, but keeping cubes at 502, will be 610-620hp.

Just throwing it out there, because if you want more, than you will need to go with more cid's or going with SC's.

personally I wouldnt tear apart 525's to make 540's, your still dealing with a restrictive plenum and TB........if you want 540's find a couple gen 6 502's ( same block ) and build away, good rotating assembly, heads, machining and assembly could be around 20K ++ for the pair, then you need all the other stuff.

Whats the budget

Promaxx 320 flow numbers

Thanks for the link. I believe these are the old Patriot Performance heads as a guy named Marty ran that biz in Alabama. If I recall they are China castings , cheap priced and one got what they paid for. Average at best at that timeframe. PP / Marty went out of biz around 2012 / 2013 timeframe.

I have no idea if the heads have changed or are the exact castings from China currently.

Also for past 4 or 5 years there is a Marine aftermarket company that sells heads from ProMaxx that puts their name on them. Not many know they are ProMaxx.