cdscarab

It really depends on how much money you can spend. For a couple grand, aftermarket exhaust (used Gills, Stainless Mar., Powerflows,etc.), remove heads, unshroud valves, clean up pockets and ports, triple angle valve job, FRESH valve springs. If the rings and cam are still good, hp should increase to near 400 and your usable rpm should stay where the pistons can live. Bigger valves would make it easier to make more power, but will shift the torque curve higher. Also, it was my experience with my 330, that it was very sensitive to final tuning, ie. how much advance, type of spark plugs, flame arrester type, even the weight and type oil used. Played with mine for many years, and saw a 10mph increase (gps) in a 90 21' Scarab. The power is there, it just takes a little extra work to get it all.

TylerCrockett

We have done several updates on the 330 HP engine. We change the intake manifold,use a modified 750 carb, change the camshaft and valve springs because the stock springs will not take much more lift. We also change the ex and add roller rocker arms and the engine makes 415-420HP with the stock heads.

Biggus

If you do all of the above and add the rectangular port Magnum heads what would be the end result?

blue thunder

It would significantly change the camshaft selection and possibly carb selection. The result at wot would be much better. The low rpm throttle response less.

BT

TylerCrockett

You would be able to use more camshaft but you can still only turn about 5000 RPM's with the cast pistons and stay reliable. If you change pistons and turn 5300 you may see 475HP.

KAAMA

blue thunder, adding the headers are really going to wake those engines up---especially in the midrange. Also, 8.4 comp ratio isn't all bad ----it just gives you a little more cushion for error.

Ragtop409, How many hours are on the engines? Do the short-blocks need rebuilding?

You're getting some good ideas here from some of these guys. Here's a rea$$$onable way of doing this, but it will depend on what the engines will need or if they require a complete rebuild. For now we will assume the short-blocks are NOT in need of being taken apart. From there, there are probably a couple of options/ways you can do this.

A good aftermarket exhaust system like Stainless Marine or GIL would be a much improved system over the stock Merc system---plus replacing the stock Merc exhaust with an aftermarket system such as I have just mentioned above will be much lighter in weight, and will really dress up the engines much nicer and they will sound much better---especially if you install a DRY system. These will allow the engines to breath easier---and the more mods you do to the engines the more the aftermarket exhaust will work for you. Keeping the oval port heads that came with the engines, have them bowl/pocket ported and have the short side radius worked on those heads, comp valve job, new valve springs. You can still retain the same valves, cams/lifters. I would remove the stock Merc "pancake" cast iron, HEAVY intake manifolds and replace them with Edlebrock dual-plane aluminum intake manifolds, and 750cfm Holley carbs as Crockett suggested. I would say you'd probably be looking at close to a 70-80hp increase with these mods. Of course you can add a lot more to these engines with larger valves, forged pistons, ARP rod bolts, larger hydraulic roller camshafts.

Let us know about the short-decks if you can, cuz if they need to be freshened up there is more helpful advice to be had here.

Have fun!

cooltoys61

Assuming you don't get into detonation or lean conditions why would a cast piston not live at 5300? Heat ? My machine shop(granted not a boat place but very experienced race motor builders) says cast pistons today are as good as forged from yrs ago and most are hyperete...whatever. I have used Hyperetectic(SP?) in other boats to around 5300 and didn't have problems. Maybe I was just lucky or didn't hold it there long enough.

Whiteknuckle

Cooltoys61
No you were not lucky. Todays modern cast parts are better than most people think. They are better than the forged parts of yesterday. People refuse to accept that.

sparky1957

I did a hop-up on a pair of 330's , they were 1989 engines. Used the original Q-jet carb, a port matched Performer intake, 224/232 degree cam,Merlin oval port heads, made 440 on the dyno. Put on a pair of Imco Powerflow exhaust and the dyno said 460 hp at 5100 rpm.Tried a Nickerson modified Holley 750 and a Dart single plane intake for a 5 hp increase to a total of 465.At this point I felt the low compression flat top pistons were limiting any more power.I never did any thing to the short block except a high volume/high pressure oil pump.Ran strong for 250 hours until one motor dropped a valve.Then i put together a pair of properly built 540's which made these engines feel weak.Moral of story:leave the 330's stock and save your money for a more serious motor, in the long run it will be cheaper and you will be happier.

Whiteknuckle

Sparky1957

There is a lot of truth in what you are saying. To soup up a 330 does take work and maybe dollar per dollar after everything is complete, one would be better off with a crate engine or a complete properly built 540 like you did. But, sometimes people can only afford a little at a time, some people just like the challenge and the final investement is not the real issue or goal.

I have been fooling around with a stock 330 now about 6 years. We are now working on Version IV. Yes, it has not been the most cost effective project, infact throwing this kind of money in a 24 ft boat is kinda nuts. I'll never get my money out of it entirely. However, I don't look at it this way. I'm having fun, its a hobbie and I do it with my sons instead of hitting a white ball around on the golf coarse.

I'll get off the soap box, that just my two cents coming from an old guy. So whatever you decide, have fun with it.