I have a 454 think its a gen 5,one piece rear main,hyd lifters-non roller,came out of 95 maxun duo prop,top of piston says 040 believe its cast,believe crank is cast also.
heres the questions,how far can this block be bored, I want to build a good little motor out of it that will run all day long,just want to go boating and not get a loan on the house,boat is fast enough and a little heavy,23' cuddy,motor run fine just tired,thought about putting in thru hull ex,will that help performance any not going to buy 3grand woth of ex,no blower no silly stuff the go fast boys can keep it,just want to ride and look at beautifull bikinis and the stuff in them,you dont have to go fast to do that,sooner or later they have to stop,just wondering,bigdaddy

If it's a 1 piece rear main seal then it would be a Mark lV block. Most people only like to go .060" over. However you can have the cylinders sonic tested for their thickness and possibly go farther if needed. Some of the mark lV's had more meat on the cylinders. I've been running mine .100" over for 8 years now with no problems and I know you can get pistons up to .125" over. Obviously you probably wouldn't want to go any farther then needed to save it for future rebuilds. As far as thru hull exhaust you probably won't notice any difference especially with stock manifolds and not changing anything else.

If it's a one peice rear main seal, it makes it a Gen5/Gen6. If it's a '95 model, It should be a Gen 5. Gen 5's have a 10 bolt steel timing cover, Gen 6's have a 6 bolt aluminum timing cover, but 1995 should be a Gen 5. As far as the bore size, 4.320/ .070 over , should be safe. The best upgrade would be to put a 4.250 crankshaft in it, 4.310 bore, and that would make it a 496. Or go 4.320 and make it a 499. This can get pretty in depth! You can give us a call for more questions !

You are exactly correct Sporl Performance about the rear seal. Sorry I had a brain fart there.

Thanks for clearing the air ..

Just went out to the shed and it has the tin cover not the aluminum one,my son say I have small rod bolts and a cast crank,cranks beautiful,not a scratch any where.
Heres another thing I dont understand,the block has a merc tage on it, the heads I am told are gm peanut small oval heads and this has a rectangle port intake thats not even close to matching anything,it has brass inserts in the water jacket and is made from aluminum,carb is webber,son wants to throw the intake in the bushes and get one that matches the heads, just want to ride around with grandma.
thanks

What this sounds like to me, is that the original motor was probably a 454 Mag , and someone replaced the long block with a stock 454.

I got some bushes in front of my house you can throw that intake in. I even got an old flat cast iron intake for those peanut port heads I'll leave out there for ya.

What's the mercruiser tag serial number?

[QUOTE=big97daddy;3278827]Heres another thing I dont understand,the block has a merc tage on it,

Since your not looking for any big power increases you may want to just want to just bore +.060, upgrade your cam & intake, maybe throw some 496 manifolds on & call it a day. I wouldn’t mess with the through hull exhaust unless you want the sound.

Check out the “330 on roids” build, I somewhat copied that on my gen 5 & picked up about 8 mph.