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View Full Version : Help with a new Prop. Engine is over reving


ciccarel
06-25-2007, 08:10 AM
I am not new to boating, but I am new to inboard Ski Boats. I recently purchased a 1987 Pro Star 190 and love the way that it handles compared to other boats that I have owned. My problem is that It is easy to over rev the motor. If I'm not careful the engine can easily reach 5000 RPM. I understand that the max should be 4600 RPM. From my experience, this is caused by a prop with too low of a pitch. I'm not sure what prop is on the boat. Is there a way to find out what prop I have without removing it from the boat? Does anyone have a recommendation for a prop that will be used for all around use. The manual states that the standard prop is 13" x 13" cupped. Any advice would be appreciated.

cm02WS6
06-25-2007, 08:42 AM
You can find the size stamped on the end of the hub, near the nut. Hopefully it will be outside of the nut so you don't have to remove the nut to read it, but that's where they're stamped. It will be difficult to recommend a size until you can confirm what its currently got, and its also helpful to know the engine and transmission. If its an older (nonCNC) prop, you can step up to a newer CNC-machined prop and pick up performance across the board.

trickskier
06-25-2007, 09:05 AM
What is your speed at 5000 RPM??? My engine turns 5300 at WOT running 46 MPH..................My 98 ProStar turned about the same............

ciccarel
06-25-2007, 09:12 AM
I was able to read the markings on the prop. It is a federal supercup 14LH18. I assume that it means 14" x 18" Left Hand. Now I'm really confused. If the standard prop is 13" x 13" why would a 14" x 18" cause the boat to over rev? Maybe the manual that I have is not correct for my 1987. The manual says it covers 1987 - 1990.

The motor is a 351 Ford. and according to the manual the transmission is 1:1 ratio. The top speed currently is 42 MPH at 4600 RPM.

I may also consider a 4 blade if that is a good option. Where do I start?

ciccarel
06-25-2007, 09:17 AM
I do not know about top speed at 5000 RPM is. I think that it is about 45 if memory serves me. I am afraid to go over 4600. Am I being over cautious? Could the tach be wrong?

trickskier
06-25-2007, 09:27 AM
I do not know about top speed at 5000 RPM is. I think that it is about 45 if memory serves me. I am afraid to go over 4600. Am I being over cautious? Could the tach be wrong?
I would have to check my manual.........But I believe the engines are rated to turn 5500 RPM's

TMCNo1
06-25-2007, 09:29 AM
I was able to read the markings on the prop. It is a federal supercup 14LH18. I assume that it means 14" x 18" Left Hand. Now I'm really confused. If the standard prop is 13" x 13" why would a 14" x 18" cause the boat to over rev? Maybe the manual that I have is not correct for my 1987. The manual says it covers 1987 - 1990.

The motor is a 351 Ford. and according to the manual the transmission is 1:1 ratio. The top speed currently is 42 MPH at 4600 RPM.

I may also consider a 4 blade if that is a good option. Where do I start?


Call Eric @ OJ Props, 1-800-359-9730 and talk with him, he will be glad to assist you getting the proper prop.

TMCNo1
06-25-2007, 09:37 AM
I am not new to boating, but I am new to inboard Ski Boats. I recently purchased a 1987 Pro Star 190 and love the way that it handles compared to other boats that I have owned. My problem is that It is easy to over rev the motor. If I'm not careful the engine can easily reach 5000 RPM. I understand that the max should be 4600 RPM. From my experience, this is caused by a prop with too low of a pitch. I'm not sure what prop is on the boat. Is there a way to find out what prop I have without removing it from the boat? Does anyone have a recommendation for a prop that will be used for all around use. The manual states that the standard prop is 13" x 13" cupped. Any advice would be appreciated.
Normal WOT for a 1987 351W with a 1:1 transmission and a 13 X13 LH cupped prop on a 1" shaft would be 4400 to 4600 rpm @44 to 45 MPH under ideal conditions. If you have a 13 X 18 prop, it should be on a 1 1/8" shaft used with a PowerSlot transmission @ 1:1.5 transmission and is the wrong prop. Just talk to Eric.

ciccarel
06-25-2007, 11:19 AM
I was wrong about the Transmission. It is actually a Borg Warner Velvet Drive 1.52:1 Ratio. Is the 14 x 18 the correct pitch? Is it also possible that the tach is wrong and it is not being over reved. When the tach reads 4600 the boat is going 42 MPH. At WOT the boat speed is about 45. This is what the manual states as the estimated top speed.

TMCNo1
06-25-2007, 11:30 AM
I was wrong about the Transmission. It is actually a Borg Warner Velvet Drive 1.52:1 Ratio. Is the 14 x 18 the correct pitch? Is it also possible that the tach is wrong and it is not being over reved. When the tach reads 4600 the boat is going 42 MPH. At WOT the boat speed is about 45. This is what the manual states as the estimated top speed.


:confused:
OK, the proper OEM prop for a '87 351W 240 HP is a 14 X18 cupped on a 1 1/8" shaft for a 1:1.52 PowerSlot Borg Warner transmission with a Top Speed of approximately 45 mph, at approximately 4600 rpm.
Now tell us what the problem is.

ciccarel
06-25-2007, 12:09 PM
I spoke to Eric at OJ props and he also indicated that the 14X18 is the correct prop. His recommendation is the 4 blade 13.7x17.5. Any opinions on 3 vs 4 blade

It is sounding more like my tach is not reading correctly. If I can verify this, is there a way to calibrate it.

trunderw
06-25-2007, 12:45 PM
I have this same boat, the 87 w/ powerslot and my top tach is about 4400--pegged, that's all she has :) I don't know how fast that is b/c I haven't calibrated the speedos, but I ski around 3100 rpms and it feels like that's under 33 mph

Would putting a 4blade on there give us any benefit?