Tunnel boat help

[homeboy6658703]

I have questions and hope someone here can help! I have a STV with 2.5 Merc (was 280 hp) built by JSRE ( should be 330-350hp), 28 pitch prop (taching at 7200). Should I be getting over 100 mph? GPS is only showing 85. I think I am doing something wrong as far as driving. Can anyone help me?

[albypine]

I have questions and hope someone here can help! I have a STV with 2.5 Merc (was 280 hp) built by JSRE ( should be 330-350hp), 28 pitch prop (taching at 7200). Should I be getting over 100 mph? GPS is only showing 85. I think I am doing something wrong as far as driving. Can anyone help me?
How can you make horse power assumptions when motor was never dynoed :D .... Not to stir the pot to bad but you may have a sick motor .. My diamond 280 out the box pushed my heavy turd over 100. If it was on a Stv I would be hands down 125+ and that motor only makes 315 on the dyno .

[homeboy6658703]

Thanks for your input. Motor is fresh, and even with stock 280 hp, shouldn't I still break 100 mph?

[motorheadbishop]

Are you on the limiter???

If so go to a big prop or get rid of the limiter...

*A stock 200 on carbs on a reg. lay up STV will spin a 28 7200 all day long, thats only like high 80's maybe low 90's.... Juss sayin

[Mr. Demeanor]

Prop type condition, engine height, gear ratio, etc etc?
My boat ran 63mph when I bought it and 85mph a few weeks ago. No change in HP, all setup.

[homeboy6658703]

Prop type condition, engine height, gear ratio, etc etc?
My boat ran 63mph when I bought it and 85mph a few weeks ago. No change in HP, all setup.
I've heard a lot of claims of well over 100 with boats like this, starting to wonder if it bs or by water speedo instead of GPS

[homeboy6658703]

I've heard a lot of claims of well over 100 with boats like this, starting to wonder if it bs or by water speedo instead of GPS
Prop has less than two hours on it, motor only has about 15 hours(freshly broke in)

[albypine]

Thanks for your input. Motor is fresh, and even with stock 280 hp, shouldn't I still break 100 mph?
My friend has a Stv with stock 280 and it runs 12? All day every day with 32 clever . He has r.o.s box that will turn 8700 .. With a 28 Et he can still run 110 . That's GPS speed FYI

[rgsauger]

My boat ran 63mph when I bought it and 85mph a few weeks ago. No change in HP, all setup.

Mr D, that's awesome! Gives me hope for my rig!

[David]

16.7% slip. There is more in set up. http://www.rbbi.com/folders/prop/propcalc.htm

What do well set up STV's run, sub 10% slip?

Post your engine height (prop centerline to bottom of pad), set back, type of prop, and someone should be able to help

[Mr. Demeanor]

Prop has less than two hours on it, motor only has about 15 hours(freshly broke in)

What type of prop? What is your propshaft height in relation to the the bottom of the center pod? There are enough of these boats around that someone should be able tell you exactly what prop at what height you should be running.

[albypine]

Compression check and pull reed cages to make sure crank is not smacking them ..... To be honest would not be first time I seen that on one of them motors

[Jay Smith]

And whats the altitudes up there in North Dakota where this is being tested?

Altitude make ALL the difference in the world 1. How ANY internal combustion engine runs and 2. How a hull lifts in thin air.. I've seen this hundreds of times..Anytime you get above 2500-3000 feet things start having running and lifting issues..This may not be an issue but I though North Dakota was a bit high in altitude...

Jay

[ModVPinND]

I don't know where he's at in North Dakota, elevation around here in Bismarck around 1650-1700 ....... he's welcome to stop by and we'll get that set-up, couple S&F er's always on the water.