502 mag mpi
 

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"..:lolhit:

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.

good point.....

If you want to make some serious power, ditch the stock intake and go with the large single plane and 2000 cfm throttle body. I know I wish I would have. I have had some serious work done to that intake and it is still holding me back. So, I get to do some more work on it this season and port the throttle body.

I think for what im looking for the 500efi intake will work great.....so......the big question is anyone out there have one for sale??? Please send me a PM if you do or know someone who does.

Which manifold?
 

I concur with Eddie Young and others here. I have done a lot of testing on 540 inchers and even some bigger cammed 502's with reworked heads and the like and even the stock EFI manifolds by Merc will top out just over 600HP with the best airflow you can squeeze from them with porting and the single mono blade throttle body.
Raylar has developed a whole new top plenum setup for the EFI manifold that we are using in our 675HP -525EFI upgrade engine exchange program and we get to 675 -700Hp depending on the cam we use.
For a simple MPI upgrade, buy the single 4 barrel throttle body EFI setup like Eddie has in his pictures and run that it will make all the power you will need with the minimum of investment and hassle. And no you don't need a 2000 cfm throttle body, a 1200 cfm will do just fine!
Ditch the MPI intakes, they won't get you there even close!

Best Regards,
Ray @ Raylar