KAAMA

iTrader: (1)

A good place to start is with a better breathing exhaust system first!

Knot 4 Me

I wouldn't touch them other than any needed maintenance. Save your money for bigger mills if you want more speed. The bottom end of those motors are not conducive to high HP/RPM's.

offthefront

iTrader: (1)

I would agree ..... run the crap out of that motor and upgrade to new power when you can ....believe it or not it prob would be cheaper .....only thing you need to watch is the stock exhaust can leak back to the motor ...not good ... ...m

Pat McPherson

I agree!
A good set of free flowing aluminum manifolds helps any big block breath; I like Stainless Marine...
And yes a K&N filter charger will also help.

To gain much more than 20-30HP will require a cam change, head work, and new pistons for higher compression.

The stock cast crank and 3/8" bolt rods are good for about 450HP and 5000rpm so there are many things you can do with your base engines...

cuda

I agree also. I bought the new exhaust for the 454/330 in the Donzi, because I have an HP 500 I planned on putting in it later anyway. Also took 90 pounds off the engine with the exhaust alone.

Big Block Billy

Slightly overheat it (or detonate it from bad fuel), and its done. Leave margin for error. If Mercruiser could have got more power from the package and had it stay together for a long time and withstand abuse they would have done it.
We must remember this is a boat motor not a car motor and works harder and must be better.
Look for 2 Mag motors or use your blocks only, with a forged rotating assy. you can use the 3/8 rods resized with arp bolts. Look for a set of 049 or 781 heads and go with the 2.19, 1.88 valves and a better cam. Everything must be balanced. If you really want to be satisfied leave the 330's stock and get everything to do two bigger motors(or find them) and use the boat until ready for the swap. This is the best advice that I can give you.

Big Block Billy

Just because someone gets away with something for awhile , it's not really worth it when it blows up.

waterboy222

Im thinking the way i might go is using the boat in stock form with just maintenance and repairs until I pay her off in the next two seasons. Then I'll refinance the boat and use that money to buy a set of larger motors. I just dont want to price myself out of the market . I'd hate to have a $40k boat with $100k worth of motors with a blue book value of $40k.. ya know?

What swap would you reccomend for this? I was thinking a set of 500 or 525's. Id like to be able to run 90 (ish) or 75 with a full boat. Am I over shooting what this hull is capable of or worthwhile doing?

KAAMA

iTrader: (1)

Yeah, lots of good ideas with aftermarket exhausts. I will admit the Merc 330 engine is not the best engine with its cast crank, pistons and rods to do an up-grade on, and even though adding a good aftermarket exhaust still may not give much help to a Merc 330 in stock form alone, it will still be the first thing you will need whether you buy a pair of slicked up 502's OR if you upgrade the 330's. Still it can get pricey when doing mods to a 330 to see a reliable increase in HP and that is why it may be better to sell the 330's in stock form and buy some engines with better internals and HP potential. However, you can always buy a better exhaust system no matter what engine you have.

I'm no engine expert, but we did a lot of experimentaion with the Merc 330 since the early 1980's or so. You can still do a decent warm-up on a Mec 330 to about 425-450hp or so @5200rpm. You just have to make sure everything is well machined and blueprinted properly. You can retain the cast crank and 3/8" rods, but I would replace the cast pistons with forged ones. Have the rods shot peened/stress relieved reconditioned and install new ARP rod bolts, and check the main saddles of the block and align hone if necessary---it's very important how that crank spins in the block! We did this with a 2-bolt main block (studs), cast cranks, upgraded 3/8" rods, forged pistons, GM oval port "049" bowl/pocket ported heads with larger valves installed and a hi-perf cam and saw a great perfomormance increase in the boat and it lasted for several years. Have fun.

Big Block Billy

Have had a 330 recently that had a broken piston skirt.
It is a problem in bigger heavy boats that sumetimes lug while planing off. Otherwise was fine and didnt have any cyl. wall damage.
Is it any wonder why most of the newer enginines have Hyperutectic pistons from the factory. No more steel inserts in the skirts. Never stop learning, it's endless and we all need to learn more. Even the arrogant ones...(not me ) BBB