I'm having my engine rebuilt complete with a new cam, lifters etc. At what point are manifolds no good? I'm looking to avoid any reversion problems. I haven't selected a cam, however if I use one similar to an HP 500, do I need headers? Is it based on the lift of the cam?? Thanks for your help!!!

Many things can cause reversion. Based on the limited info in your post I would say you don't need headers, but I'm no expert.
Dave

Buy a set of gen 111 stainless marine from SPEED AND CUSTOM MARINE....Talk to scott he is about the cheapest and a great guy that wont bend ya over......The single most important upgrade you can make is good exhaust....I would not think of running reg merc manifolds on a 500 hoarse motor you are chocking it off from all its potential......IMHO.........If you are putting these on a single engine mag pm me i can help ya a lot with the install and might be able to hook ya up with a set of tail pipes cheap.....

hi robert call crane cam talk . to frank he can tell you what cam to put in your motor i built a 480 hp 454 ran stock manifolds for a year ran ok then i got ss headers motor ran better and cooler pick up 300rpms if you got the money get the header

What cam and what cubic inch engine???

Robert, 500hp cam will need headers.A lot of overlap in the cam is what draws the water back. The 454/365 magnum way back when had reversion problems. Merc added pieces the the elbow to mix the water further down stream as a band aid. Like others said money on headers at is well spent. Even more if you have motor done accordingly.

Thanks everyone! The engine (block) is a 1979 427 tall deck, stroked out to a 496. The crank is a welded steel keikhiefer (sp) with I beam rods. There was a little pitting in one cylinder due to reversion. I'm planning on having the block bored, decked and alined. I'm planning on a new crank, rods, pistons and bearings. On the top end, I'm planning on hyd. roller rockers and a new cam. I haven't decided which cam, any suggestions? The engine will be going back into my 24' Sunsation raceboat, so I'm looking for top end performance. Down the road, I'd like to upgrade to rectangular port heads.
Jim, I don't know if you remember me, I was with Mark H. when we met you after looking at the Sunsation raceboat-several years ago.
Again, thanks for your information and opinions!!!
Bob G. "Lock'd Up" Racing 606

If you're not exactly sure about what to do for a cam, then another option would be to call "RMBuilder"/Bob Madara of Marine Kinetics in N.Y. for your cam. He has helped a lot of guys on here with hi-perf marine offshore cam applications. Bob is an expert at taking all the necessary component info that you're using in/on the rest of your engine(s) and will come up with a cam profile specifically suited for your needs and engine application. Have fun.

Bob's number.....(585) 654-8583