Okay, was wondering what ,aufacturer and #, 'steel shim' still doesn;t tell me much. Some are steel with no sealing layer, some have a rubber outer layer to seal,and etc.

Anyway, so, steel with no sealing layer you always want to spray copper coat or etc for sealing.

What caused the MLS gaskets to go ?

Looked back, I used Felpro steel #1094. They are .015 compressed., they're plain, no layers or coating. Perhaps the poor install on the first HG's caused the marks on the heads. Cuz you don't hear about MLS gaskets failing.
And I put the cam at zero from the crank. So if it's like yours it 110 degrees or if it's as designed it's 109 degrees.

Yup, plain steel always needs a coating of something. Way back, it was aluminum paint, until they came out with the copper spray, hi tack, and Holomer (sp?)

Some of the steel shim gaskets need a finer RA deck like MLS believe it or not.

Sure it's not cooling or high compression/detonation issues failing these ?

Could be cooling and/or detonation but there's little proof.

When I first ran the engine I ran it kind of easy with a lot of rpm change, trying to seat the rings properly. I don't think it passed 3300.

The first time I really let it rev I was coming north between Long Island and Moultonboro Neck, my absolutely home territory, toward the Long Island Bridge you mentioned..
So I cracked the throttle to 90% for a couple of seconds. Speed built immediately, I was stoked, wind, awesome sound. Check gauges, and its 210. Pulled back and shut down, I had blown a hose off the feed line. And there was 8" of water in the bilge.
It hadn't got to the starter or any electrics, I pumped it out, reconnected the hose and went along cautiously. But in hindsight, that, along with dry stainless head gaskets and single torque, could have all been involved.
Also, remember the original Thunderbolt V has knock sensing to control and manage timing advance. The TB V came with a cast piston 350 and I was running it in my stroked, forged piston 383. So there's the possibility the knock sensor would not identify knock in my 383. So if that was involved it could have been detonating, Who can hear detonation in an open pipe boat? Not me.

I have addressed those things with a plain ol' all- in-at-3000-rpm ignition, heads were skimmed, gaskets were copper coated, heads retorqued after first heat cycle.
Fingers are crossed now,. As I said, after setting the cam from minus 4 to straight up, it ran on the stand with no measurable water in the exhaust manifolds.

Revisiting this thread to let folks know that the engine has run right this season.
It has always had 93 octane fuel. Now it has the plain HEI ignition from Davis Unified (DUI) at 30 degrees all in. I may go to 32 degrees, but meh?
I ran it to 4500 yesterday on the way down the lake and it was happily accelerating til I backed off the stick.
And I have to say I really enjoyed how the boat acts at upper speeds. It feels solid and controlled even when it gets a little lift off some of the lumps in the water. It wasn't enough to break prop grip, more like unweighting feels when you are in the middle of a turn or a bump snow skiing.
Then it idled down the canal into the marina for 10 minutes without issue, where the last 2 years it has fouled plugs through there.
So I feel a little better.
I don't have a weekday off for about ten days, weekends middays have too much chop for me to run max speed.
I will probably will do the full pull when there's a weekday off, or if I am on the water early on another day.

did that fix the reversion ? I am battling something similar. I sold my 383 to a buddy I swapped out cam to basic stock size cam out of his 300hp vortec marine motor. I used cloyes timing set and it has crossed my mind that might be my issue but then I get guys telling me the extra stroke will cause reversion. I'm in the middle of making dry to tip tails for his stock manifolds .just wondering if I need to pull motor and check gear. Thanks

Oops long time between answers. Yes no more water in chambers. Buuut, remember I also took off that Thunderbolt V ignition. And I also needed my heads resurfaced. It was a very small cut according to my machinist. And I have sent him heads from the shop where I am assistant mgr for years.

thanks . I ended up useing a cam comp said "should" work but still was getting reversion . ended up making dry to almost tip tails.are you still running stock manifolds?

STart new thread and tell us everything and anything.

"I get guys telling me the extra stroke will cause reversion." I wonder if Mercruiser knows this? They have built the 377-383 for years with no reversion problems.:lolhit: