496/8.1 is closed cooled. After running in salt for several years, my exhaust manifolds (not part of close cooled) were almost perfect. After breaking, building and wrenching on my 496's the only things that made me nervous IF THEY ARENT BEAT ON is the valve springs, they are painfully small. With the heads off on the floor, I could stand on the valves and open them... Their seat pressures have to be insanely low. BUP can you comment - at 1000 hours is a valve job or new springs in the manual as maintenance?

My buddy has 2000 hours on his 454Crusader motors in his 86 Silverton . Run like new. No oil burn no smoke, no noise.

And they are just 350 horse pushing 22000 pounds at 20 knots.

My brother has over that on his 454s in his 1985 39 Searay . They smoke a bit and burn some oil.

Most likely just need new valve seals being they are 30 years old.

If you don't overheat them or run them out of oil , you can't kill em.

I always find it funny how people think all I/O's are not reliable. Low HP ones can run a ton of hours. Like I said we used to run 351W motors in our ski boats for thousands of hours with just water pump rebuilds and oil changes.

And those were run hard, WOT at take off and when in a salom course jacking the throttle harder then a off shore boat.

Stock 496 taken care of shouldn't be a issue.

I believe it Monza, I got 3000 hours out of a new small block Mercruiser motor and sold it and it ran another 10yrs after. Fresh water tho.

I had a 496HO in my 2004 Superboat Y2K. Ran it 1 ur stock. Put a Whipple charger on it. Ran for 5 yrs. Sold to a friend who ran it 2 yr s. Sold it to a guy back in LI.who is still running it. No problem s.

It sure seems stock maintained low horsepower marine engines can live a long time. I have 1997 twin 502 MPI Magnums in my 38’ Powerquest with a tad over 1000 hours that run perfect. Nothing has been done to them other than run in fresh water only and normal maintenance. I have noticed no deterioration in performance or any more oil consumption since I bought the boat 11 years ago with 230 hours.

I prefer the 502 to the 496 , however , stock vs stock , i would say your 500% less likely to experience the head gasket -valvetrain failures that usually take down the 502s. It appears they solved the oil ring issues on the 496s also. Plus being a oem suburban -1 ton pickup long block , the potential to replace a engine that did grenade and had no core value, can be done on the cheap (compared to the 502) it is more expensive to upgrade though.
If the engines sound good on the cold start (24hrs ) hatch open no misfire rod knock lifter tap , they are likely healthy and will live long glorious happy lives

That was true of hte 496 but its getting harder to find the block now. Unless of course you buy one from DART with a 4.5 inch bore. :)

Sorry I missed this my bad. what is explained in the manuals for the 496 and I am going off the top of my head here is Yes they want you to check Valve Spring tension.

They do not give any intervals but will add they give a special note. They wanted you check spring tension ---- the springs should be replace if NOT within 10 lbft of the spec. It was according to their procedure and valve spring testing tool and torque wrench. Also installed height of the valve springs 1.828 thru 1.869 inch to be checked. I remember that

Open spring tension was an average of 200 lbft / 880 n but would have to look this up to be exact of the ratings because it was a range like 185 to 210 but do not quote me exact here as I would have to relook that up to be 100 % the average was close to 200 lbft. This is per Merc, per their service procedures, per their OEM service manuals for totally STOCK apps

I briefly ran not owned one commercial parasail boat with a 496.

Thing was way overpowered for the hull design [. 28 wide body Premium ]. Would have been great with a different gear ratio in the drive, early model .

So why did GM go to this new block and what as the advantage over the old gen blocks?

I know the Mercuiser packages are freshwater cooled all the way to the the exhaust manifolds so other than that what are the advantages of them over the old style 454 -502 blocks for marine use?

I've heard the disadvantages that they are not rebuild able.

What's the consensus from the guys that have done mods like Raylor and others? Did it dramatically affect engine life ?

The Mods have only been out a few years so any longevity info would be great.

I was not impressed with the one I was running as it experienced multiple sensor failures over and over.

To me the old 330 horse 454s were like a Model T.

The mechanical fuel pump would usually give you a few weak moments to give you a warning before it totally died.

The ignition systems were pretty low maintenance for being out in saltwater . Loved the fact that when the wiring or the keyed ignition acted up , which is 98% of your electrical problems on a Saltwater boat ,you could run a positive to the coil and roll on.

The Rochester carbs were bullet proof.

The old style raw water pumps were good when they were brass, the plastic crap not soo much.