Ok lets say im building a 509 and keeping the MPI with good heads like afr 305's, stainless marine exhaust and a mild custom cam that should make peak power around 5400 rpms and horsepower between 550 and 575. Ive done a lot of searching and realize my stock black 502 intake is very restrictive. Most say its only good to 575-600hp without any port work done. Does it make sense to change it to a 500efi intake or have a bunch or porting work done or will I not see any advantages as long as im under 5400rpms and 575hp? Not sure if it will effect me or not where the rpm and hp range is??? Thanks for the help.

Rob, When I was building the 415/502 everyone I talked to said no matter what you do to the intake & plenum it will do little or nothing. That's why I bought the 500 EFI setup.
Talk to Jason or Bob Madara @ Marine Kinetics 585-654-8583. Both will give you all the information you'll need.
Good Luck
Jake

BTW, I thought you were going to stay "STOCK"..

Yeah, when I thought about making my 502s into 540s, everyone said to find the HP 500 manifolds because the black manifold is so restrictive. I think smitty did some huge mods to one and got some good power from it, but that was hugely labor intensive and it would be easier to buy the good manifolds.

put a single plane manifold w/ 2000cfm throttle body and be done with it

I switched my 502 MPI to the 500efi intake. I also made it a 540 with AFR heads and Bob Maddera cam. M.E.R performance in Little River SC. and Bob Maderra have a package they are puting together. My motor made 693HP on the dyno with this package. Jeff Wurl

Could not agree more. That is what I do to the majority of them. Even the 500 efi intake has it's limits at a little over 600 hp, without mods and a larger throttle body. Eventually, you will end up at the limits of the intake. Spend a little more up front and get an intake that really doesn't have limits. You will then be set for any future mods and not have to spend the money twice on intakes. Here are a few pics of ones I have done in the past. These were all 502 mags at one point.
Eddie

I think the valve covers will still be "stock"........although I will probably paint them.

thanks for ther info guys, I do understand the intake is very restrictive but do you think it will hurt me at the HP and rpms im running? Just wondering if it flows enough for what im doing or not. Not looking at making over 575hp max and I dont want to spin anything over 5400 anyway.

It was too restrictive for Merc to use on a 500EFI. Even the 500EFI intake is restrictive and can't support much over about 600hp.

I used the stock intake and inj. reflashed ECM . 515 CI stock heads ported with bigger valves,mild cam,stainless marine ex. 525 on the dyno at 5200.