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Old 10-20-2009, 07:35 PM
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Originally Posted by TRBenj
Another boat guy, cool!

Either increase the revs or increase the cubes, right? I would think that either would help take better advantage of the 990's. I dont want to prop down, but Id be OK turning in the 5500-5800 range- but Id need the hp to get me there (probably 50-80hp since Im turning about 5200 now and it takes 10-15hp to pick up 100 rpm).

Stock compression ratio on the marine 330hp 454 would have been about 8.12:1. The HO version (390/425hp) would have been around 8.6:1. Again, I dont know what Ive got now as who knows what it was rebuilt with. I guess we'll have to pull the heads to find out, right?

Assuming Ive got a pretty tame cam in it now, would I stand to make any gains with a piston (to bump CR to ~9), cam, intake manifold and exhaust change? Again, I dont want to do anything that will hurt holeshot.

Ill look into the Kodiaks, as well as other (used) header options. Ill go with 4" if at all possible... though I REALLY like the look of the logs. Ive seen minimal gains with high $$$ headers on a BBC (330hp, otherwise minimal mods) and a flow test which proved that some ported aluminum logs can outflow ported cast iron center riser manifolds on a Ford, so I had hopes I could make a little bit more power with them (and save some weight at the same time), while adding a cool look for not a lot of money.

Heres a shot of the boat in action, just for fun.

Hey TRB, I think you're a pretty sharp dude but, maybe you need to do the math on prop changes. Okay, first I agree there is no substitute for cubic inches, the bigger the better. I also agree that more CI will help your rect. port heads act smaller in respect to boosting torque. You need to think in terms of torque in respect to boat engines rather than HP. A boat does not overcome it's mass like something rolling on wheels. Once you get a car moving it takes less torque to keep it moving faster and faster till you run out of gear ratio or HP. A boat on the other hand really never overcomes its mass.
Getting up on plane is just the action of rolling over the barrel of water that forms under the boat when you're trying to get it moving. Once you get the boat on top of the water, the drag is more constant. If you trim up, you get less boat it the water and less drag. Do you have the full size trim plate on the transom, is it fixed, adjustable or what?
As far as more RPM are concerned, it does not do you any good to prop for more RPM if you're decreasing pitch to get there. You did say a smaller prop,
which leads to the math on prop changes. You said you had a 13x14 and a 12.5x15, these are super pulling props w/1:1 drive but if you want more speed you gotta go up in pitch as in 16",17",18" to gain speed. Every inch you go up in pitch is gonna bring the revs down but what you're hunting for is the sweet spot in the torque that can still turn the prop at a speed desired. In your case, you can probably still go up in prop pitch, gain some speed and not give up too much low end pulling grunt.
If you still want to give up some cash and build a stroker motor, cool. But you can likely gain a little speed with a prop change, still pull skiers and only be out of the cost of a new prop.
Examples; 14" @ 5000 w/20% slip=53mph
15" @ same=56.8
16 @ same=60.6
19 @ same=72.0mph
You gotta see what it will spin up to with different props.
example; 19"@4600 w/20% slip=66.2
Food for thought, speaking of that, its supper time, later.olnolan
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