Cam help please

[68r/t]

I am about to start building a 505 stroker motor for a 16 ft ski boat that had a 383 in it  and I,m stuck with the cam selection,
Here's some specs of what I have got already.
440 source stroker kit, 10.6-1 comp
440 source heads
rpm manifold
Holley 850 dp
the limiting things are it needs to be hydraulic and I'm using the standard style  rockers,
Its also got the watercooled manifolds, what were looking for is a torque monster that will have a max rpm of about 5500 rpm.

I've gone through the proven combo section and got a few ideas but can anyone recommend a cam for this combo?

[BSB67]

Inboard or sterndrive?

Submerged exhaust?

What is the planned use?

I assume it is fresh water use.

[68r/t]

It is an inboard with submerged exhaust and will no be using a water to water heat exchanger as its all saltwater where I am,
It will be used to pull a couple of skiers and tubes etc, with a the occasional high speed blast   most of the ski boats around here are gm powered so we wanted something different.
I think the biggest limitations are the stock rockers and the exhaust.

[BSB67]

Okay.

I would shoot for a 5000 rpm max.  Peak power 4600 to 4800 tops.  Use a 750 cfm carb.  An 850 is too big for the marine use you are intending and will hurt the bottom end power which is usually more important for any water sports.  Possibly consider a smaller intake if you are wanting to wake board, wake skate, wake surf or other big wake, slow speed operation.Cam with too much duration will push the power band too high, and will suck water into the motor coming off plane at an idle. 

I would not use fast rate cams, use something more moderate.  I would stick with something no bigger than 270 advertised duration with a 112 LSA.  You need to prop-up to take advantage of the power for top end speed.

The few older inboard ski boats that I have been in don't really do high speed very well.  They tend to porpoise and seem to have too little lift/too much hull in the water. FWIW.

[Challenger340]

16 Foot
Low Lift....but very long seat to seat duration, 112/114 Lsa. mushy old style stick if they are still made.
The stock rockers may not like the 130# seat and 290# over the nose @ .500" lift on the Stealth springs, nor the stock pushrods, but without a little head clearancing the 3/8's pushrods don't clear either, so you may be stuck ? or order better pushrods...then better Rockers....

[XH29N0G]

May I ask how fast your boat will ultimately be?  

I have an old (1979) 19 foot tunnel with a 200 hp outboard, but it is really too heavy to really get up and go the way it should.  I hope to try an 3 liter on it to see if it works better.  My dad has a modified V (also 1980's/70's design) but it is about 800 lbs w/out motor and can get enough air to lift it high enough to let it run well (90's) with 250 ish HP.  The next project is a late 50's DU with a 25H (my dad has a 55H he wants on it) - we are learning about magnetos right now.  

Sorry I don't know about what cam would be best.  Double sorry for the partial hijack.  Good luck with your project.

[68r/t]

Thanks for the replies, yes the boat is small at 16 ft and  at around 800 lbs with out motor, I don't know what speed it should do as the 383 was worn out when we got it so we haven't driven it yet.
The boat would be around 30 years old and was originally used for an offshore race we had here in Western Australia called the Fremantle to rottnest race which is approximately 13 miles long.
The 383 hit water when we went  to bore it as the saltwater had been eating away at the iron over the years  and the 505 hasn't cost a great deal more than doing a 440 which is why we have done it as we only had a bare 440 block and the extra torque should be great.
The 383 had a comp cams 280H which is a single pattern cam with 230@.050 and 480 lift.
I was thinking of a comp cams xe 274 which is 230 and 236@.050 with 488 and 491 lift but is on 110 lsa
I was originally thinking of the lunati voodoo type of cams with around 230-240 duration and 530ish lift as I thought 500 inches would absorb that up easily but now  I,m not sure  since you guys are saying low lift lazy style cams.
So what do guys think of the XE 274?

[XH29N0G]

Didn't realize you were in WA.  I am almost on the other side of the world, but had a chance to visit your area for a few months in 2012.  Travelled all that way to use scientific instrumentation at UWA.   Hope to return in the not too distant future.

Freemantle to Rottnest in a 16 foot boat seems nuts to me, but I also thought that about a lot of things I saw.  Not in a bad way - In a good way.  It is a nice part of the world. 

Must be a pretty sturdy and speedy boat and should be a lot of fun.  I assume you ski in the Swan river.

[BSB67]

I have to admit, What I in vision as a "ski" boat is about as opposite as you can get from a offshore boat in my mind.  I believe that you used both those terms to describe the boat.

Anyways, I made some use/performance assumptions when you called it a ski boat.  I'm thinking emphasis on reliability, low maintenance and good performance in both acceleration, low end power and decent top end.  Sounds like I was mistaken.

All that aside, you can certainly use fast rate cams, and should use one if max power is what you are looking for.  You can use high lift as well.  These are harder on the valve train but will make more power.

In my opinion, the XE274 on a 114° is about the most you should go unless you want to get into the weeds on the latest on what is working in reversion prevention and how that applies to what you are doing and what you have.  Exhaust design is key as well and I doubt that your manifolds have the latest in reversion prevention.  Guys are running 280° ish cam (220° to 230° @ 0.050") on 450 to 500 cu in engines but are also using the latest header designs.  Some use 60° overlap as a rule on late model stuff.  Bleed down lifters like Rhodes or Crane Hi-intensity are commonly used as well to reduce the idle overlap.

Don't make the mistake that what works in a car works in a marine engine.  These are endurance engines and the build considerations are different.

[68r/t]

Yes, i must admit I wouldn't like to take it offshore unless it was a glassy day on the water which is rare over here,
It will be used as a recreational ski boat on the swan  river mostly, the exhaust is old tech and in the future will be updated to a much better system, I think I will go for the 274 ground on 114 lea which comp cams said they will do.

xh, glad you enjoyed this part of the country as most visitors do the east coast as everything's a lot closer together but there's lots to see over this side if the distance dosent bother you.