Vette,
I did pull the plugs and look at them, however the engine was cold.
There was an indication of water droplets on a few of the plugs. I also cranked the engine with the plugs out and about a 1/4 teaspoon of water came from a port side plug hole. It shot all over the side of the engine compartment.

When I pulled the starboard side manifold, the back two exhaust ports were wet inside. Port side manifold was dry. Also my engine guy had relayed to me that the intake valves and seats were horribly pitted and need replacement.


Paul

I have run cams as large as 228/235 @ .050" on 112 LSA and have had no problems with stock manifolds. Where is your idle set? If it is just barely running the possiblity of reversion is even greater. Even on a 110 LSA 215 duration is really short and shouldn't be pulling back very hard on the exhaust. It is amazing how much condensation is produced when a motor is first fired. You should double check the plugs once the motor is up to temp and run for a while.

Sutphen30,
Heads are already off being magnafluxed and pressure tested.

Paul

Not wanting to beat a dead horse, but overlap is the time in crankshaft degrees that both the intake and exhaust valves are open. It is not an absolute number, but is measured at a specific amount of lift. For example, overlap at 0.050" lift, .006" lift, .004" lift. Its very hard to measure overlap at 0" lift because there is no overlapat 0", but a fraction off of 0" is your largest overlap. See Bajalion's example.

I have no hard evidence for this, but I have heard that marine engines should have less than 7* of overlap at 0.050" (assuming riser to waterline height is correct). If you look at the .050" overlap of stock Merc cams, you'll find that they don't overlap at 0.050". I'm shooting for 1* at .050 for my 383 thru prop: 218/224@110

Cam Profile
 

FYI attached is the sheet PB requested.

I have always run a 224 , 232 at 114 cam, #1 intake at 106 which is about +4 timing, with no reversion on stock Gil magnum choice risers BBC which are as close as a stock Merc. As was already stated, if you are close, you can increase your idle speed. Dont go too high if you have a Bravo, it wont like it.

Two cams using the same LSA can have very different overlap numbers because overlap is a function of the duration of the intake and exhaust lobes. Here is an article that may help clarify the subject.
http://www.chevyhiperformance.com/te...98/index1.html
Hope this helps,
Bob

Thanks, cool site!!!

As you increase intake/exhaust duration and/or decrease LSA you increase the number of crankshaft degrees that both the intake and exhaust valve are both open. Reversion occurs when both valves are open and the pressure area (pulse)downstream of the exhaust valve is greater than upstream (combustion chamber, intake port, manifold) The longer a period this condition occurs (increased duration/overlap) the greater the opportunity for water in the exhaust passage (mostly from manifold cooling water exiting into the exhaust stream) to be drawn into the combustion chamber. This is an extreme simplification but hopefully it will help explain that reversion occurs due to a "spring effect" beginning at ambient above the carburetor and ending at ambient at the exhaust exit.
Hope this helps,
Bob

LOL!!! Dont ask me how this cam works,,, but it is wonderful thing...It was made by a very well known cam mfg for his family boat,,,said he had to have a cam that sounded "good" and just happen to make two of em, Just running stock exhaust...I can tell you that the exhaust closes 7° before TDC and intake opens 8° after TDC ,,,,, intake closes 38° BDC and exhaust opens 48° after BDC.