5.7 260hp 14.25x21 WOT 5200+ whats wrong

[red85k100rs]

I have a 1981 Sea Ray SRV225
Motor: 5.7 260hp
Drive is an alpha one 1.50
At 4700 rpm speed on gps is 40 mph
I have currently have a 14 ? X 21 aluminum prop (new)
The boat weighs 3800 pounds dry and no gear. Add 70 gal gas, oil, tools, anchor, lines, life jackets cooler with ice and beer, and all the other stuff I carry on board I would guess 4500+ pounds.
When I got the boat it not been run in 2 years, but the little bit of fuel had stable added. It had a 14x17 stainless prop and it had a hard time getting 4000 rpm at WOT. I changed the fuel filter, cleaned the spark arrester (it was completely clogged with what looked like lint), new plugs, wires, added 3 bottles sea foam to the fuel (about 50 gal of fresh fuel).
After running most of the fuel out, the boat would climb very quickly to 5400 rpm (would have kept climbing but I throttle down. So I figured I needed a bigger prop. I got a 14.25 X 21 prop thinking that should bring the rpm?s down. Well it didn?t, maybe a little. It still will climb to 5200 quickly, and would go higher. The boat jumps out of the water! It?s up on plane in about 75 feet with 4 people on board.
Should I try a 15x21 or 14x23 or?

Thanks in advance for any advice.

 

[Bamaman1]

Re: 5.7 260hp 14.25x21 WOT 5200+ whats wrong

Your motor should be running between 4400 and 4800 rpm's. It sounds as if you need a 23 pitch prop to get the rpm's down.

If you look online, there are some websites that can guide you on the proper pitch. You would need to find an accurate boat weight, which should also be available online.

I have a local prop shop that gives good free advice if you're buying props from them. They'll also let you take 3 props to the lake to test before you buy. A large online prop shop in Florida also allows swapping props after taking the boat to the lake.

If your boat is in very good condition, it warrants investing in a stainless steel prop.

 

[Silly Seville]

Re: 5.7 260hp 14.25x21 WOT 5200+ whats wrong

There is something very wrong here. I know exactly what kind of boat you have, and the numbers you are giving are near next to impossible. Either your tachometer is giving inaccurate readings, or your props are misidentified or your outdrive gearing is not 1.5:1

Or you have a very built engine that is turning greater numbers than factory. Something to consider. BTW, that boat weighs @ 4500lbs. dry!

 

[red85k100rs]

Re: 5.7 260hp 14.25x21 WOT 5200+ whats wrong

The prop is brand new, I took it out of the box, I also checked the numbers on the prop before I put it on, and I know it is 14.25x21. My srv 225 doesn't have the raised cabin, or port windows. I have searched and searched and found 3800 dry weight. But I just looked all I could find was at the NADA site it list it as 3440lbs dry. The only work done to the motor that I know of was to get rid of the points. It does have a 4barrel carb, but I am guessing that was original to the boat but I don't know for sure. Also, it came with a pre-alpha but I broke that. I replaced it with an Alpha One gen 1 outdrive came off a V8 and is stamped 1.50. Also has 898 stickers. I don't know allot of history on the motor. The guy I got it from didn't use it much and did nothing to the motor. He has a wellcraft with twin 350's that he always used.

@ 4700rpm what should my speed be?

Where I boat I am on a river that the channel is not as deep as it should be, it usually is 6-8 feet deep. But with the lack snow over the winter and lack of rain this year, it's only 4-5 feet and there are places that are less and I have hit bottom in the middle of the channel. So I don't want a SS this year. (The Fox River in NW suburbs of Chicago). So a prop shop wont let you test/damage props on the river.

 

[Maclin]

Re: 5.7 260hp 14.25x21 WOT 5200+ whats wrong

I would verify the drive ratio. The numbers you give calculate to a 2.0 ratio assuming 15% slip on the prop.

 

[aerobat]

Re: 5.7 260hp 14.25x21 WOT 5200+ whats wrong

i agree with the posters . no way 260 horses will spin a 21pitch with a 1.5 drive to 5200rpm. if you would you should go ballistic- 60mph or better.

so eiter you have another drive ratio or your tach is wrong.

cheers

 

[red85k100rs]

Re: 5.7 260hp 14.25x21 WOT 5200+ whats wrong

I will check it tach, the boat is in the water still so I won't be able to check the drive untill the end of the month when I pull it out of the water. thanks for all the info and advice. I will let you know what I find.

 

[Silly Seville]

Re: 5.7 260hp 14.25x21 WOT 5200+ whats wrong

Your outdrive upper gear casing is stamped 1.5, but in reality the ratio may be different because anyone could have changed the gearset in that housing. When the boat is on the hard, it's real easy to check your ratio.

Also, the easiest way to check your tach, is to go buy a quality automotive tachometer like you see the gearheads using on the dash of their hotrods. Simple to hook up to your coil and battery. Run engine and compare the dash gauge readings with the new tach. You'll have your answer. DON'T forget, all modern tach's have a dip switch for 4-6-8 cylinders. Check it!

http://www.sunpro.com/product_detail.php?pid=16325