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Skir68
07-19-2011, 02:57 PM
Anyone know what max rpm's on this motor is?
I'm running a14x18 prop with a Powerslot transmission.
I was told I should be doing 41mph. The rpm's are 5000 at wot!
Seems way to fast to me but motor is silky smooth!

east tx skier
07-19-2011, 03:39 PM
The 88 Pro Star Manual lists Max RPM at WOT at 4,600 for the 351W.

Skir68
07-19-2011, 03:55 PM
Thanks ETS! Is that the 1:1 or 1:1.5?? Is there a diff?

east tx skier
07-19-2011, 05:39 PM
Thanks ETS! Is that the 1:1 or 1:1.5?? Is there a diff?

Max engine rpm is not transmission dependent.

1redTA
07-19-2011, 08:28 PM
I have an 81, 240 hp 351W slot and a 14x18 and mine will turn 4300-4500 max. borrow a gps and see what the speed is at max rpm

j.mccreight@hotmail.com
07-19-2011, 08:30 PM
yep my 89 is 4600 at 45mph

MasterKraftS&S
07-19-2011, 08:57 PM
1984 S&S, 351, Original(or damn near) 3 blade 14:18, 4600-4800 WOT - 40MPH GPS Confirmed. Not satisfied, planning new carb in the Fall. Whats the next BEST thing to boost power/Speed. Getting older and heavier(me not the MC)

need more speed to make up for my poor barefoot form.

Jim@BAWS
07-19-2011, 09:00 PM
1984 S&S, 351, Original(or damn near) 3 blade 14:18, 4600-4800 WOT - 40MPH GPS Confirmed. Not satisfied, planning new carb in the Fall. Whats the next BEST thing to boost power/Speed. Getting older and heavier(me not the MC)

need more speed to make up for my poor barefoot form.

REPROP

Intake manifold

thatsmrmastercraft
07-19-2011, 10:17 PM
REPROP

Intake manifold

Then GT-40P heads

east tx skier
07-19-2011, 10:43 PM
What the last two said ... in that order.

MasterKraftS&S
07-19-2011, 10:48 PM
Ok, Prop, Manifold, Heads, AND we'll proly add NEW Decals from BAWS this Fall - That's bound to help SOME!! :steering:

Skir68
07-20-2011, 08:44 AM
I'm trying to keep our MC reliable as well! I have 4 kids who need that thing so we can ski every day! They would be let down if we couldn't ski cuz the motor needed to be rebuilt!

Wouter
07-20-2011, 08:50 AM
1990 351w GT40P Acme 13: 4800 RPM - 46 Mph (after discovering my secondaries weren't opening)

thatsmrmastercraft
07-20-2011, 08:54 AM
1990 351w GT40P Acme 13: 4800 RPM - 46 Mph (after discovering my secondaries weren't opening)

Failed diaphragm?

Skir68
07-20-2011, 09:01 AM
So is running at 5000 rpm's bad for my Motor?

Wouter
07-20-2011, 09:08 AM
Nope: Did a carb rebuild a long time ago and forgott the little cork o-ring between diaphragm housing and carb... Never realized (I'm ashamed to say) the secondaries weren't opening untill recently browsing through some posts and realizing my RPM at wot were really low. Not that I go to wot much on the track. Made me have a good laugh at myself though...

Wouter
07-20-2011, 09:11 AM
Skir68: I don't think you would reach 5000 RPM very often if you're using the boat to ski or wake or tow anything else (except barefoot perhaps)... Skiboats aren't made to operate at wot for long periods of time

thatsmrmastercraft
07-20-2011, 09:11 AM
So is running at 5000 rpm's bad for my Motor?

It's about 9% over red-line. It wasn't designed to turn quite that fast. There is certainly a fudge factor built in to the suggested max rpm. It won't make your engine last any longer. How much it will shorten the life is a tough to say.

Wouter
07-20-2011, 09:14 AM
+ where do you read this 5000 RPM? tachs aren't always very reliable...

Dino Don
07-20-2011, 09:31 AM
Then GT-40P heads

Agree heads for sure but the cam on the 285 hp has more lift and duration--which you need for better breathing and performance.??????????????

thatsmrmastercraft
07-20-2011, 09:42 AM
1984 S&S, 351, Original(or damn near) 3 blade 14:18, 4600-4800 WOT - 40MPH GPS Confirmed. Not satisfied, planning new carb in the Fall. Whats the next BEST thing to boost power/Speed. Getting older and heavier(me not the MC)

need more speed to make up for my poor barefoot form.

Agree heads for sure but the cam on the 285 hp has more lift and duration--which you need for better breathing and performance.??????????????

For what he is looking for, a prop, intake and heads would be more than enough.

Skir68
07-20-2011, 09:58 AM
That's where the 5000rpms is coming from, my tach!
How else could I read it?

Wouter
07-20-2011, 10:02 AM
For what he is looking for, a prop, intake and heads would be more than enough.

Second that + it's already a few 100$ upgrade and less difficult than finding a matching cam and switching it...

Wouter
07-20-2011, 10:03 AM
That's where the 5000rpms is coming from, my tach!
How else could I read it?

From an automotive multimeter or perfectpass if you have it.

thatsmrmastercraft
07-20-2011, 12:02 PM
+ where do you read this 5000 RPM? tachs aren't always very reliable...

That's where the 5000rpms is coming from, my tach!
How else could I read it?

That sounded funny but was a fair question. If the tach in your boat is off by 400 rpm @ 4600 rpm, this whole discussion wouldn't have happened. Might be worth checking your tach against another.

Skir68
07-20-2011, 12:09 PM
What snot trying a 4blade prop vs a 3blade? That make a difference?

east tx skier
07-20-2011, 12:16 PM
To get the best prop for your application, you will need to know what your engine rpm is at WOT. So double checking that number is the first step.

Skir68
07-20-2011, 12:27 PM
I'll stop by Napa to see if I can rent a multi meter from them.
That's a good place to start, your right, I need to know how accurate
My tach is before I wind up blowing my motor up!

Wouter
07-22-2011, 05:35 AM
I'll stop by Napa to see if I can rent a multi meter from them.
That's a good place to start, your right, I need to know how accurate
My tach is before I wind up blowing my motor up!

Might be worth buying. Trust me, you will use it again :D