buck35

Fresh gas and fuel filters? How long since it was run before you bought it?

88corsair

It was ran a week before I bought it. Fresh fuel. All new filters in June have the receipts for it all. Fresh oil change too.

airjunky

iTrader: (2)

Make sure its still hitting on all.8 and the firing order is correct . Not a whole lot of simple mods for the ole truck motor with a non emissions cam. Besides aftermarket heads-intake swap.

skillets

You are down a lot of rpms. This would be the first thing I looked into. With another 800 rpms I would think 50 plus mph would be no problem. Try another prop

SB

iTrader: (1)

For a baseline, what are these boats supposed to run with that motor ? And what prop as delivered from manufacturer ?

88corsair

The boat is suppose too run around 50 55 and from what I can tell a 21 pitch prop. It now has a 23 pitch prop on there and should of picked up a little but since day one never went over 40 with either. I really think I have a hurt motor. There is no hour meter and I have no idea the last time she was taken out and rebuilt. I picked the boat and my myco trailer up for 4K with paperwork so at that price I thought it was too cheap but I used it about 20 times but my season is over for boating here.

Ghost24

When you say she is dry, how are you assessing this? With a moisture meter? Weighed trailer with and without boat on truck scale? How do we know the boat isn't overweight? When I suggest the coring might be soaked, you wouldn't have any way to know this short of moisture meter testing, invasive testing, or weighing the boat.

Respectfully, while I agree the motor is way on RPM, It's only a bit down. Max recommended RPM range for that motor is 4200-4600. At 4k, you're only a bit down.

I'd bet big against the prop being the main issue. If you're supposed to be getting 50-55 and you're getting 40, you're either heavy or you're down on power, or you have some drag source. If it's all lack of power, you're looking at a 100-160HP deficit to lose that much speed. It's likely not the prop, especially down at at 21 or 23 pitch where you are. That's near the bottom of the typical prop pitch range. Something would have to be WAY out of whack in your gearing setup to make a 21/23 so much too tall. If you had a 32 pitch on it, I'd listen to that.

Figure 12-17HP per MPH. The 10-15 mph you are down means maybe 100-160 HP off of your stock 310/330. The max HP RPM range for that motor is 4200-4600. You're not far off it at 4000. At 4000 with a healthy motor, I'm estimating you're probably down 20 or 30 HP from peak HP at 4200-4600. If you're only down 30 HP, it won't cost you 10-15 mph, it'd cost you 2-3 mph. If you're 10-15 mph down from where you should be, I don't think it's a sick motor UNLESS you should be swinging a MUCH bigger wheel with a healthy 330 horses. If it's a sick motor, you'll need a bunch more pitch once it is healthy again.

Gotta believe you're down on power or the boat is heavy, or both. But given your RPM are only a ways down from the peak HP RPM range, I'm thinking it's at least partly weight/drag unless you're actually UNDERPROPPED.

phragle

iTrader: (3)

a 23 on that big of a boat with a 330 is too much prop.

Speedracer29

Agreed. I had a 230SX Stingray, shallower deadrise, 45 more hp, 3-400lbs lighter, and swinging a box stock 23 Mirage Plus barely put it into the warning buzzer.

Ghost24

Respectfully, unless I missed it, we don't know the gear ratio of the drive here yet, so we don't necessarily know what is too much wheel.

4200 is the bottom of the NORMAL WOT operating range for the 330HP 454. (4200-4600)

Doing 4200 with the 21 suggests that prop has the motor within the normal setup range IF the engine is healthy. Perhaps you'd want to go down as low as 19 to bump up to 4600 RPM when wide open, but that won't jump the speed up from 40 all the way to 50 or 55. Not even close. You might get 2-3 mph out of it if you're lucky. The horsepower at 4200 should be pretty close to the horsepower at 4600. A bit lower, maybe, but very close.

HP is what pushes a boat to a certain speed. (People get very confused about torque, but HP is king. Gearing is how you make use of the horsepower. Gearing takes an available horsepower budget and sets it up for a certain application. If you want to buy a Coke from a vending machine, you need the $2. The $2 are the horsepower. Gearing changes it's application to the task, like having 2 1$ bills versus 8 quarters versus 200 pennies. There are gearing setups that make it impossible. Like 200 pennies. That won't make your $2 work to get the coke. Nor will a $100 bill, even though you have plenty of money. But the 8 quarters, or 2 singles or lots of other things, will. HP = speed. Gearing fits that available HP budget to the task, by getting the torque and RPM where you need them.)

Something is wrong with this boat. The original hull, if intact and not waterlogged with hundreds of pounds of soaked coring, should do more than 40 with a properly set up 330 HP 454. The power must be lower, or load must be higher, or both.

If the measures here are accurate, I'll bet the boat never did 55 with either of those props. Perhaps it did 50. I suspect the motor is sick and perhaps the boat is a good bit heavier than it was when built.

Do you know your drive gear ratio? What type of drive is it?