Really.....how might I tell if mine is a candidate? Its an 01' HO.
I assume the pistons are still cast?

The 496 doesnt appear as an option for GM trucks at this point. A 6.0 is the biggest gasser. I think the issue is that more people are going to oil burners for pulling applications b/c gas cost. The 502 wasnt an option in older chevy trucks, only the 454. Yet gm continues to pump out crate 502, 350's etc....even the 572. I dont think the BBC is going away.

Just because the 496 isn't a light-duty truck option doesn't mean it will die altogether. There's also a big market in industrial use...John Deere makes something that uses the 496/8.1L
For the future of road-going vehicles...face it, diesel/electric just might be getting to the point of being the overall best option and we'll see big gas motors in trucks go away. That doesn't mean someone can't come along and keep building blocks...they'll just cost more.

Here's some GM Powertrain Marketing for your review.

http://www.whygasengines.com/

Its true that the 496 -8.1L engine is used in more (other) applications such as Marine, medium duty truck and motorhome, industrial and such than were ever used in GM pickups and suburbans that were so equipped.
The current plan with Mercury, Volvo, etc., for a new 2008-2009 marine high performance marine motor is for an GM LS 6.0 motor iron block (heavy) with a supercharger to get 425 to 450 hp. These motors will be equipped with new emissions systems as well in the form of catalytic converter, closed loop efi fuel systems.
Hold on to you wallets, they are going to be expensive! and they will have to use boost to get the bigger torque numbers needed. These new motors are going to be a challange, even for the likes of Mercury Marine to make them work and stay together for the warranty periods.
Don't let anyone bull**** you , boost under load in a motor reduces ring pack and engine life!!
Remember these smaller cubic inch supercharged motors (364 cubic inch) will have to be in almost full time boost to make the 400-500 foot pound torque numbers needed for high performance and larger recreational boats.
Being supercharged under boost these engines are going to use more fuel in marine applications.
Why are Mercruiser and Volvo and others going to them, they may be the only GM Powertrain engines available for them to marinize! Remember, only Mercury Racing -Fondulac builds special engines for Mercury, not Mercruiser in Stillwater, Oklahoma.
This almost constant boost scenario is going to have a serious engine life issues and it will take a few years before the report card will be in.

Hoverver in the mean time, we dummies at Raylar have been engineering what we feel is a more reliable replacement. If you go to our website www.raylarengine.com you will see a tab for the LSM550 engine. What is it ? Its a 450 cubic inch all aluminum small block GM-LS derivitive engine we have developed. How does it work? Pretty neat! produces 550HP and 510 ft/lbs of torque from a 7.35 liter closed cooling- ALL ALUMINUM engine that weighs about 450 pound less than a 496HO or HP525 big block or other standard big block marine motors. This motor is naturally aspirated (no blower or supercharger), runs on 89 pump gas and is a completely "blueprinted" with all the best forged internals engine and is equipped with variable cam timing, big oil coolers, our own special stainless 4 tube headers and lots of other goodies! This new engine size-packages for a boat, narrower, shorter and lower in height than current big blocks .

GEEZ! Imagine taking 1000 lbs out of the back of your twin engine hull and still having 2 x 550 hp to play with.

We wil start shipping the new LSM550, as soon as we complete our durability testing (Secret). How much will they cost , in quantity to boat builders about $22-25K fully equipped less drives Considering the cost of Mercury Racing's HP525's and Ilmor 525-625's that are likewise equipped and produced, we feel they will be a real breath of fresh air for the marine high performance boater.(no supercharger pun intended!)

The other nice thing about our LSM550 motor & testing has shown that standard Bravo 1 and Bravo 1X drives are just the ticket for a reliable drive package, no need for big expensive aftermarket drives or Bravo XR drives!!
For those boaters with older twin engine iron small block equipped boats this new engine makes a wonderful retro-fit motor and the horsepower increases and weight reductions are still there!
We will have this new engine on display in Miami this year as we couln't get it there in time last year while it was being premiered at the LA Show. Funny though, very few people even realizred what it was!
Pretty Cool HUH! We think so, but Hell were slightly biased!

Best Regards,
Ray @ Raylar "Where innovation fuels applications"

www.raylarengine.com/lsm550

Thanks for the viewpoints. I'm not looking to do anything crazy - if I were I'd build something from scratch. So neither the 502 or the 496 have any forged rolling components? I just saw a 2001 boat advertised with 502 mpi HO motors - from the photos it looks like the air cleaners are different. My 2001 Merc brochure has no listing for this - did such a thing exist or is this a "home made HO"?

How much would it cost to take a standard 496HO to the 525HP range?

The 496 is cast the 502 is forged.

I've heard glowing rewiews on the 496's engineering improvements to ease maintenance, but don't understand why Merc brought this motor in. The 502 was around long before the 496 and I'm pretty sure the HP 500/525 is still based on this foundation. Now there's talk of the 496 going away. Was the 496 introduced into the lineup just to satisfy economics / profit margin, like they were getting a deal on them from GM?

Mild Thunder:

Our 103 kits for the stock 496HO take the motor to a real 525HP with stock exhaust and stock ECM. Add a good header system and you are at 565HP. The kit sells for $6360 and with most installs being about $1600 to $1800 range per motor. (Pulling the motor and re-installing)
We can reprogram the rev-limiters in the stock ECM and give you a 5500rpm rev-limit instead of 5150rpm.

As for 502 Mercruiser engines , I believe some like the later model 502EFI- 415 HP versions had forged pistons and rods, and forged crankshaft (5150 alloy not 4340) crankshafts. The rest of the 502's and 454's MPI's and EFI's from Mercruiser had cast pistons, forged rods and cast crankshafts.

The 496 engines from GM all manufacturers have GM cast hyereutectic pistons, forged rods that are smaller and weaker than the old 7/16" GM forged rod. They have a cast pressure rolled fillet - fully counterweighted cast crankshafts that are very much stronger than the older GM cast crankshafts. These are probably equal in strength to the older GM 502 (5150 alloy forged crankshafts.)
Some of the early 496 HO engines -2001 had a forged crankshaft with the same GM forged rods and cast pistons.
Raylar has forged crankshafts for the 496 and these are the ones we use in our HO525 and HO600 short blocks and long motor combinations along with our forged Raylar/Mahle pistons and special H-beam billet rods.

Hope this info clears some questions with some answers.

Regards,
Ray @ Raylar