Where Did I Go Wrong, Cam? Intake? Carb?
 

Scratching my …. Trying to find out what component is not playing well with others. :(
It just runs out of power at 5,000 RPMs.
Boat is a 90 22’ Pachanga (light boat) started with the 330HP turned 4,500RPMS stock
Rebuilt the 330HP with new cam, 781heads, bumped compression to 9:1 gained 200 RPM

Last spring I stroked the engine from 454 to 496 using same components and gained 100- 200 RPM.

I thought last fall heads where not flowing enough and smaller valves. So over the winter I replaced the 781 large ovals heads with the Edelbrock’s(larger valves and intake runners)and in doing so bumped compression from 9:1 to 9:5. Result 100 RPM gain. I would think I could get that with the weight savings!
Jetted carb up 2 sizes on both primary and secondaries(its not running lean)

Last night I switched from a 24 to 27 pitch prop to see if I had plenty of power to push it to 5,000. Only turned 4,500RPMS and same speed GPS. It had no problem getting the boat on plane, plenty of low end torque.

Current engine
496 – 454 stroked to 496
9.5 compression ratio
Edelbrock 110 CC large Ovals 2.25 &1.88 valves
Intake – Edelbrock Performer Large Oval
Carb – Bary Grant Sea Demon 750 D.P. 80 primary 88 Secondary
Cam – Comp Cams Xtreme Marine XM270h
226 236 @ .050 .544 .547 on a 112LSA
Holley fuel pump 7psi -8 lines. Its not running out of fuel.
K&N 5x10 filter its not running short of air.

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

wheres your timing set at?

looks like a good build overall. The heads are the only thing I would question.

Have you tried a smaller prop to see if it will twist it higher? I think your just running out of power not cam/heads etc.

Lab the 27 and spin it to 5k.

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

What exhaust are you running?

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

As far as parts selection, I'd get rid of the Performer intake. It's choking you. I'd at a Min get the Air Gap RPM, and with your components and boat size I'd strongly recommend the Dart Oval Single Plane.

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You have not answered about exhaust. At this level you should have good manifolds like Stainless III's or headers like Lightning or CMI. Those boats came with those water lift mufflers right ? I'd get rid of those and go straight out.

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Then , if you do both above, later (if your rotating assembly is strong enough) I'd put more cam in it and let the boat fly.

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

I agree with SB's first statement. Your getting into the larger displacement and now you need runner volume.

2nd I would put 1.8's on the intake valves and get that thing some lift. Duration is the ability to sustain an rpm. . .lift is the ability to get there.

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

Timing is at 34. Trying to avoid a meltdown. Plugs look fine.
I running 91 octane so I did not want to press my luck with the 9.5 ratio.

Exhaust is IMCO POWER FLOW

Chris, I know there has to be better cams but changing the rockers to 1.8 would show and increase?
Larger runner volume are you talking intake? The heads are 290 now.

I was spinning the same 24 prop with the 330 at 4,500. There has to be a min of 100 HP after these changes.
Still looking for valued opions.

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

It would get the valve off the seat quicker and start the cylinder fill. All of my marine cams for the CID you have are all in the low .600 lift range. Yes I think it would make a difference.

The intake itself you need more runner volume. The Air Gap I feel is the best all around intake and would make an excellent choice. An unported Dart/Victor I think would also be a good canidate for the combo especially since you have a light boat. I have a used Dart Oval single plane.

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

definetely go with the performer rpm or air gap- don't go single plane or you will kill all of your torque, i am getting ready to do the same change on my pachanga, it runs out of steam at 5000 and i have the same intakes, also i am running 34 degrees total timing

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

This is simply not true. A big cid motor needs airflow. Most single plane intakes will not kill torque on a 496cid+ engine. In fact, most build ups will make more where you want it.

The Dart Oval Single (+rect for that matter) are near perfect for Marine BBC's. Plenum volume's are quite small, runners are quite long, runner CSA's are not too big, fuel distribution is quite good, etc,etc,etc.

Yes, this is based off of many dyno tests and many on water experiences. Most marine performance engine builders will agree. The shear amount of 496-540 marine engines that have been built and tested in this country alone is staggerringly high.

Re: Where Did I Go Wrong, Cam? Intake? Carb?
 

BigJim,
The IMCO's are much better than stock, but with the improvments you have made throughout your engine they are really not doing you any favors at this point. I've have kinda been through what you are doing, and at this point you would see a vast improvement with a set of true headers.