When I was removing the manifold bolts some weren't tight. I never heard any leak noises though. Why would a leaky gasket cause this?

My thought would be if you have less exhaust pressure due to a leak water has a better chance to revert, just a thought, definitely not an expert on this.

Looking at these photos I would think if it was reversion the rust would be a lot worse than the pictures show. The rust would be more concentrated .I would thinks its condensation on cool down or running it on a garden hose. Last November 2014 It was cool outside 50's and I ran it on a hose to fog it. After fogging the engines I put the boat away for the winter inside my garage. The engines were close to operating temps of 150-160. Cold water in the manifolds and risers and heat from the cylinders during cool down has to condensate IMO. I'm not going to worry about it..Back together it goes today... Its been this way for years and runs great

Thanks for everyone's input

Have you looked at your bores with a borescope. If not try an borrow one or purchase or pull a head on the worst side. Something just seems strange. I just can't imagine your cams causing any issues but then again....

Now that your aware of it you'll more than likely isolate the problem.

Or you'll put it back together and try and forget you ever pulled exhaust,

Or put dry pipes and and once again solve one problem and create another.

Good luck and keep us posted on any new findings. Call emi or Hardin marine tomorrow and see what they say.

Could very well be reversion issue but my gosh I would have to go back and look however if I recall they looked similar to 454/420 hp cams.

Condensation.

Next time you winterize or run on the hose maybe cut off water supply just for a second or two and crack the throttles before storage.

I plan on calling Eddie Marine tomorrow and forward some pictures to them. If you look back at the begining of these posts there are 2 photos that someone posted of reversion. The rust in those pics are concentrated in one area of the port. Mine are a bit spread out like it was a mist of water not water itself.

This is the first time I ever heard of silent choice setup ever causing a reversion problem. ;)

Its not the silent choice, its the cam i;m using with the silent choice

Are you sure those are the correct cam specs???? Don't know of a Crane with those specs. Flat tappet or roller????



Bumping up the idle about 100 rpms will help some.

Thanks I'll try that. Here are my cam specs.a few numbers off from my original post



Crane Cams 134241 - Crane Cams Hydraulic Flat Tappet Camshafts Details

Big Block Chevy 396-454ci 1967-95

Notes:
1980 and later engines should use 271-96801 springs and 271-99957 retainers at an assembly height of 1.800".
Good mid range torque & HP, fair idle, moderate performance usage, mild bracket racing, auto trans w/2500+ converter, good w/plate or manifold nitrous system, marine applications; primarily used in 350+ HP mildly modified engines with free- flowing above water exhaust systems for performance applications, responds well to improved cylinder heads. 3200-3600 cruise RPM, 9.5 to 11.5 compression ratio advised. Good w/centrifugal or Roots supercharger, 10 lbs. max. boost w/8.5 max. compression ratio advised.

Grind Number H-286-2 (Replaces CCH-286-2)
Operating Range 2400-6200 RPM
Duration Advertised .286°/.296°
Duration @ .050" Lift 226° Intake/236° Exhaust
Valve Lift with 1.7 Rockers .534" Intake/.553" Exhaust
Lobe Separation Angle 112°
Max Lift Angle Intake: 107° ATDC
Exhaust: 117° BTDC
Open/Close @ .050" Cam Lift Intake: 6° BTDC (opens)
40° ABDC (closes)
Exhaust: 55° BBDC (opens)
1° ATDC (closes)