I have a 540 with 630 lift cam 236 344 dur and AFR 315 cnc's on it I have Gill manifolds on it right now and i am considering a set of lightning headers. Can i expect any improvement with the lightning's or shold i just save my money and get a set of sport tubes? I have a slight crest to get over depending on the amount of weight in the boat and water conditions. With two people i can get really good slip numbers and 90 plus but when i get to the 5 plus people i seem to be stuck around 80 moh 5500 rpm and i cannot get past it.

Hpy,I'm running afr 315's on my 540 w/slightly less cam and my lightning headers reverted water BAD. I had to go to stainless hi tq 3's with the water injected right at the exhaust tip. I would look at a different brand as lightning will even tell you that their headers can revert worse than stock exhaust. The Afr's seem to compound the problem,Smitty

thanx Smitty. Do you think there would be much of a HP gain in these? What about CMI Sport tubes? In other words i am thinking about spending some cash. Dose NE1 have any 1.8 roller rocker arms laying around? how about a better intake say a Brodix or even a team G rectangular port. Something any thing is better than a Holley Strip Dominiator intake.

Most cyl heads on bbc's have 60-65% I/E ratio,your afr cnc 315's have a more ideal i/e of around 75%. Its important that you have exhaust that flows enough to let the heads work. I don't ,however,know what the best exhaust is. I do know that I had std lightnings on my merlin headed 540 with a procharger,it picked NOTHING up on the top end over the stock merc cast iron manifolds,far from the 600 rpm's I thought I'd see. I did gain midrange tq that you could feel though. I replaced my heads w/afr cnc 315's while upgrading motor last year,motor reverted water so bad at idle testing in the driveway that it would literaly cough and stall with water laying in exhaust ports. I replaced lightnings with stainless marine hi-tq 3's w/5 inch tails. They fit terrible and look like crap,if I was doing it over again I would have bought the best cmi's that I could get. The boat is also so loud with the big tails that I absolutely had to buy mufflers,thats my limited experience with marine exhaust,Smitty

Big tube true tubular headers

CMIs or Stellings.


Dont feel bad I need to get two sets of 2 3/8 id headers.

Maybe they will be under the christmas tree.

I had a similar situation.. I built a new 540 last winter. Simliar to yours, AFR 315 CNC heads, .578 .608 lift, 236 * 248* @ .050 , 114 * lobe seperation. I had Gil WetOffshore manifolds and pipes. They reverted water real bad. I went to CMI headers and wet tails, they reverted a little. Then I went to CMI full dry tails. Problem solved, but got real loud. I ended up with GGB Extreme mufflers as well. They bottom line, I saw no power loss or gain at all with any of these changes..

That was my next question. I have Gills now and everyone i talk to said i should be reverting like mad but no sign of it. So i guess i am just going to stay with what i have. Maybe an intake and different rockers to increase the cam lift a little. If the budget allows i will be giving fred a call and getting a set of sport tubes...... I really need hyd steering anyway.

Hey smitty do you have a pic of your headers?

This is what the lightnings looked like,motor looked good enough to be in a magazine. I'll look to see if I can find a pic of the stainless marine hi tq 3's,they are ugly and look cobbled with hoses and 90's running in every direction. They are so big I had to cut snout off supercharger and put offsets on valve cover breathers plus hack up the overhang on the transom. Alot of cussing and pain was involved in installing them,Smitty