Ran-Dom32,

Depending on how far you want to go will obvisously depend on how much money you want to spend. Sounds like you're looking for a 5mph increase and that you want to work with most of what major parts you have there now.

With your 330's you probably have the stock "peanut port" GM oval port heads with the stock 2.06" intake valves and 1.72" exhaust valves in them. You can take those heads and have the larger 2.19" stainless intake valves and larger 1.84" stainless exhaust valves installed in them. This will be good for about 15hp. Or you can keep the stock size valves, but replace them with stainless steel valves. WHATEVER size valve you decide to go with, make sure you have the heads "pocket/bowl" ported. Install bronze wall valve guide liners---these will usually don't wear as fast and are more forgiving than the stock steel valve guides. The guide heigth may have to be machined to clearance the lift of the new cams otherwise the retainers may hit them during engine operation. Have a 3-angle valve job done. Replace the heavy, stock cast iron piece of junk intake manifold with an aluminum dual plane intake manifold (Edlebrock or Wieand). Install a new hydraulic cam/lifters with something like a 222* intake duration and a 230* exhaust duration on a 112* lobe seperation angle. For the new cams you'll need new valve springs to match. I would add a some moly 10* retainers and machine hardend locks. Do the engine a big favor and replace the stock stamped steel piece of junk rocker arms with a set of aluminum roller rocker arms. The stock GM stamped steel rocker arms won't allow for the bigger lift and duration anyway. "Scorpian" brand makes a decent rocker arm (blue colored) for what you're doing that are reasonably priced. Add new true double roller timing chains sets. Replace the stock pistons with new forged or hyperutectic pistons. The stock cast cranks will be fine as well as the stock 3/8" connecting rods. Just have the stock rod bolts replaced with an ARP "wave lock" 180-190psi bolts. If the block needs boring have the shop use a torque plate when they finish hone the cylinders. Make sure they check/measure the main saddles and have them align honed if needed.

Just make sure you have EVERYTHING checked and MEASURED with a MIC by a reputable, competent performance machine shop that knows how important the difference of .0001" of an inch can make. Have the entire rotating assembly balanced.

As far as aftermarket aluminum exhaust maniflolds go, it is probably the most important thing you can do to help the performance of an engine---they help the engine breath better and are usually cast aluminum which makes them MUCH lighter. The stock Merc cast iron exhaust manifolds are very CRUDE breathing and are extremely HEAVY! Stainless marine or even Gil marine makes a decent manifold. Stay away from aftermarket manifolds that have only a 2.5" collector and/or have a riser that has 90* bends and a poor primary design within the manifold. Buy a manifold that has at least a 3.5" collector and elbow shaped risers/tailpipes. Adding the cams, intakes and head mods will help your engine(s) and you still might even be disappointed, therefore until you add performance exhaust manifolds to those mods I have given, you're probably not going to see the KICK IN THE PANTS performance that I think you're really looking for. My .02 of course. I hope it goes well for you.

Ran Dom- Is your boat all yellow???

the 330 on steroids route is a good combo... go with what Crazyhorse listed and keep the at 5500 or under for RPm's and use a good machine shop!!!!

Crazyhorse, Dyno and I are all on the same team actually----Team Chaos that is. We've all put our heads together for these souped up Merc 330 combinations that work.

Thanks for all the suggestion's guys - roughly how much $$$ are we talking? Correct me if i'm wrong but would'nt it be cheaper to buy a used pair of 502/415's such as the ones in OSO classified's for $15,000/for the pair. I'm not sure I have the mechanical ability to do a rebuild. If I have to pay someone to perform the surgery on my 330's - I may be better off pulling out what I have?
I have to way to cost. My main concern is reliability - are these 330's going to hold together @ 450 - 500hp 5500 RPM or are they wicked? I'm located on Lake St. Calir bordering MI -how reasonable is Tyler Crocket??

I had about 6K in mine 2 years ago....I had one set of Merlin heads, but I bought EMI exhaust also.....thats for two motors !most engine guys around here get 800-1000 to assemble them.
I had one MSD ignition and bought one more....You can pick up some parts off the board or if you get lucky some one might sell a set of 502's but they arent cheap....

OH and one more thing we are getting about 250-300 hrs before rebuildimg them......very few problems....

I got 10MPH with twins......

I too have taken a 330HP 454 and done significant upgrades. The best advice, is good quality machine work and attention at assembly. I had my block align bored, new ARP rod bolts, .030 over with hypernuetechtic pistons, new 3/8 push rods, cam, lifters, and roller rockers. I have tried two different cams and two different sets of heads and two different intake manifolds, and I'm still not happy. The dyno figures look pretty good, but the actual performance in the boat has been disappointing.
Before you do this, I would suggest that you figure out how fast you want to go, then figure out the power you are going to need to get there. Then, see if it is feasible to do all this work on the 330's or get a couple crate motors. I'll be happy to share any info with you.
Good Luck

Hey Whiteknuckle what are you running for exhaust? you should be around 500 hp depending on your heads and exhaust.....3--5 mph I jumped up 150 hp in a single engine application and gained about 5