:D No problem I am still new to the high performance end of all this.I got Dennis Moore's book on the stuff and found it to be a real eye opener.In the book it talked about LSA and it stated that if the LSA is kept to within 109-112 an acceptable idle but one with a slight lope will be maintained and only a slight if any amount of water will be sucked back into the combustion chamber at idle.Mercruiser has suggested on there high per. engines that after extended periods of idleing the engine should be revved up a few times before it is shut off to clear any water.It did not say what exhaust was being used,I went with the stainless marine exhaust even before I had gotten the book and made my cam choise and with it dumping so far down the line I feel I should not have any problems .I do rev it up on long idles and before shut down.

FloridaSon, I think these guys are calculating based on 0.050", so if your numbers are also 0.050", you should be at 9* of overlap.

FYI, the cam recommended by Comp for my 350 with stock exhaust was an XE-256-12. This has 212/218 at 112, which gives no overlap at 0.050" (-9*). Out of morbid curosity, I looked at Comps Extreme Marine Rollers: XM264HR=-9*; XM270HR=-3*; and XM276HR=3*. The XM270HR is the largest recommended for an I/O.

Interesting thread.

220BR Thanks:cool:

I purchased Dennis Moore's book prior to rebuild,I figured 108 would work? I'll have to check and see if duration is rated at .004, .006. or .050 Iknow comp cams rates at .006 , I'm using melling.

Floridianson, are you using stock manifolds? Cpperformance makes an 's' pipe, which dumps further downstream, I wonder if it will bolt up to stck manifold?

Useing the Stainless Marine:cool:

220BR or anyone help me here I wish to learn.I called Crane and he said to look at the cam card.Now in my case I did not get a cam card.I went with the GM cam12366543 the ZZ502 from the local dealer and was real disappointed that it had no card and no numbers on it that could be traced back to a dam thing.(like a box of cracker jacks you never know what you will get)I do have an old cam card from my old motor so INT.opens at 34BTCD closes at 66ABDC and EXT.opens 78BBDC closes 30ATDC so what do we add or subtract to find the over lap.Also I had Crane look at the MER.500hp cam with 222-230 LSA110 and he said it only had 6* of over lap.Thanks :cool:

There's at least two ways to calculate overlap, but both require the LSA. I looked up the GMPP cam on the web and found that its duration is 224/234 at 0.050" but the LSA was not listed.

Using durations, just add the two together (224+234=458), then divide by 2 (=229). Dividing by two gives you half the duration on either side of the centerline. Now, double the LSA (because its in cam degrees not crank degrees) and subtract. So, for LSA of 108, overlap =13*; LSA=110, overlap=9*; LSA=112, overlap=5*

Good Luck

220BR, I checked with corsa, cpperformance, and melling. All of them were concerned with duration only, they have two trains of thought, of course there are no definite numbers! They say anything over 230 degrees dur., or an engine that will not idle, is cause for concern!

There are guys on this forum with a lot more experience and knowledge than me on this, but if your spin a conventional outdrive (Alpha, Bravo, etc...) a lumpy idle makes docking manuevers a pain. That seems like a very aggressive cam for a 355 I/O.

IMHO, for a boat, your better off making power thru displacement than an agressive cam. Why not turn that 355 into a 383?

Good luck