Prop issue??

[Bigdave196]

I have a 22' Blue Water Ski boat, open bow with an Alpha 1 GenII outdrive powered by a mercrusier 5.7L 300 HP motor. Motor reciently rebuilt.

I have been running a 19P Quicksilver SS Prop and after my motor rebuild I cant get the motor to spin past 4000 RPM. Carb has been rebuilt, Motor is timed, and I am looking for the answers.

The local prop shop told me to change it out to see if there was prop "hub" slipping. So I went to my backup prop which was the original prop a 17P aluminum prop. I gained 300 or so RPM's and about 5 mph.

With the 19P Steel Prop I am turnng around the 4000 RPM mark @35MPH, and with the smaller 17P Im around 4250-4300RPM's @ 42MPH depending on trim and water conditions. All speeds are at WOT.

The Boat was well in the 50-55MPH and 5000 rpm at WOT.

 

[QC]

Re: Prop issue??

I have a 22' Blue Water Ski boat, open bow with an Alpha 1 GenII outdrive powered by a mercrusier 5.7L 300 HP motor. Motor reciently rebuilt.

Carbed? Who told you 300 bhp?

The local prop shop told me to change it out to see if there was prop "hub" slipping

You need a new prop shop. Spun hubs make RPM go up . . . Waaaaaaay up

The Boat was well in the 50-55MPH and 5000 rpm at WOT.

This was prior to the rebuild? With the same 19P prop? If so, this is not a prop problem; most likely you have engine issues. This assumes that all of the data you have supplied is accurate.

 

[solar7647]

Re: Prop issue??

It sounds like a motor issue not a prop. Is the motor idleing at the proper RPM. It could be as simple as a carb adjustment. If the carb is fine double check the timing one tooth can make a big diferance. Good Luck, you may want to move to the engine forums.

 

[Randybeall]

Re: Prop issue??

Ok, you have a problem, we need some more information to give you correct answers. What was the boat/engine performance before the 'rebuild'. What prop, what rpm, what speed, and is the speed with GPS or speedometer.
I would suspect that you got a rebuild with less performance than orignal. Perhaps not the same cam grind, pistons with lower compression, if the heads were replaced perhaps they were not as orignal. Quality of valve job alone can hurt performance above 4000 by an unbelieveable margin. Anyhow, give us the before and after numbers and you will get a straight answer.

 

[Bigdave196]

Re: Prop issue??

Randybeall, here are the answers to your questions in order.
1. Boat performance was easily 55mph, by spedo, which was only 2-3 mph off by GPS.
2. Prop is a SS Stiletto 3 blade 19 pitch. Been on the boat for 10 years now. Engine speed was 5200-5500rpm at WOT.
3. Engine was supposed to be a 300HP rebuild. the origional factory motor had 220HP and we would see results as posted above. Now we cant get the RPM's over 4200 and GPS speed above 45 MPH.

 

[QC]

Re: Prop issue??

Engine problem!

 

[Bigdave196]

Re: Prop issue??

QC,
engine purrs like a kitten and roars like a lion. Just only to the tune of 4200rpms. I talked to the engine builder and he says that he has never heard of a marine engine running over 4500 rpms. He also explicidly states that my engine has been built to 300 horsepower. I asked him what he thought about me having to drop prop size and pitch to get my rpm's up and he saud that its not uncommon to do so at my altitude. (5500' above sea level) yet when i had the boat at 2500-3000' above sea level where i based my comparison from he said that I should get my 200-300 rpms back according to what he feels is the rebuilds potential. My engine was turning 5000 rpms easily and the boat moved with a purpose. My friends in their 26'-28' cuddy and aft-cabs are faster than I am with a SBC and a bravo outdrive. Im a 22' skiboat with an alpha outdrive and less than 1/2 the weight and displacement.......
ARRRGGGG!!!!

 

[hwsiii]

Re: Prop issue??

It could be many things, but check the butterfly in the carb first and be sure it is completely vertical when it is wide open, that is a very simple test and the cable may need adjustment.


H

 

[QC]

Re: Prop issue??

The reason I am so emphatic is that you already have all of the info to make an assessment . . . .

Same prop, now boat goes slower and less RPM. The only answer is that there is less power going in. I am a little confused about the altitude, but IF the performance numbers degrade at the same altitude with the same prop, then power is lower . . .

You need to repost this in the I/O section and follow everything there for low WOT RPM. Either the engine you had before made more power, this one makes less, or the tach and speedo are wrong. I see no other variables.

 

[Bondo]

Re: Prop issue??

Ayuh,... Basically,... A prop is a Dynomometer,....
It measures your Horsepower by the rpms at WOT...
While the Altitude is No doubt a Factor,...
At this point you have Less Horsepower than you had before the rebuild...

 

[Bigdave196]

Re: Prop issue??

Thank you all... Several of you have helped me with this issue since the rebuild went into the hull. After looking at every possible issue then I can only conclude that either the engine kit was mis-labled or I was taken for a ride by the reputable engine/machine shop who rebuilt the motor.

I am going to go to a 15* prop here and see if I can squeze those last few hundred rpms out of the motor and see if any increases in performance happen.

This Site ROCKS, and the responces I have recieved have been responces that real people helping people stay in a passion of thier lives.

Thanks guys.

 

[QC]

Re: Prop issue??

After looking at every possible issue then I can only conclude that either the engine kit was mis-labled or I was taken for a ride by the reputable engine/machine shop who rebuilt the motor.

Mislabeled? What part of it? Cam? Maybe . . . Taken for a ride? How? Improper assembly?

I don't get this . . . EVERYONE tells you that you have power issues , you conclude something is wrong ^^^^ and you go to a 15" prop? Dave, Dave, DAVE!!! STOP!!!

I just read through all of your original thread. Several people have mentioned possible cam or valve train issues without one reply to any of that. You need to start over!!! I have not seen one post where you have actually followed any kind of proper troubleshooting procedure. I am not usually this blunt, but you're blowing it man. Throwing Carbs and ground wires and propellers at a problem that has NEVER been diagnosed.

 

[hwsiii]

Re: Prop issue??

Dave, I just now saw that you are running the engine at 5,000' elevation. Did you have the carbs rejetted for that altitude, that could definitely be a problem.


H

 

[QC]

Re: Prop issue??

Yeah, but I think he is saying that the comparison data from the previous engine to this one was all at 2500 ft. or so . . . I am still a little confused by that.

 

[hwsiii]

Re: Prop issue??

QC, I have seen definite weird results from moving from one elevation to another. I do most all of my propping by mathematical calculations, and I even take into account elevation, when I know there is elevation involved. In my new query for information from new people I even ask if they are at an elevation.
But I have seen some definite prop problems arise that I could not account for mathematically, so I try to be real careful when I deal with those cases.
But there is an easy way for Dave to check the motor and see how it compares to the old one, and that is to bring it down to the same elevation he ran the old motor at and see whatever differences there are now.
Mercruiser offers what they call something like a high elevation kit, and all it does is change the lower unit to a higher gear ratio to create more torque to help the engine.
But I do agree with you QC it appears that nothing has been done to find the problem and correct it, and it could be a simple fix. If it was me I would be bringing it back to the shop and have them Dyno the 300 HP for me and prove it. But even with that it could have the wrong cam durations etc.


H

 

[QC]

Re: Prop issue??

But I still think he is telling us the results that he is comparing were at the same elevation, not the 5500 that is being considered? That's why I am now confused . . .

 

[pinecrestwoods]

Re: Prop issue??

If it was me I would be bringing it back to the shop and have them Dyno the 300 HP for me and prove it. But even with that it could have the wrong cam durations etc. H

If they'd do that, great. Maybe they could give you a "tuning session," if they do that sort of thing. If nothing else, pay for a tuning session (I'm assuming that's available for marine engines, but I don't know). A session would be cheaper than new props.

Yes.... tach could be off.... but I would think that you can feel 1k rpm and 10 or so mph (I can). This was supposed to be quite an INCREASE in power. Dave, you didn't have a 600lb. passenger or two, or three, did you? Otherwise, your rebuild should be able to turn that stinkin' prop (19p) even easier than your old..... rpms should go up, and you could technically go up a prop or two?

Hopefully, the engine builder is familiar with marine applications and will understand the significance of WOT and rpm. Ask him more questions, don't accuse anything, instead, get him on board and use him as a tool to diagnose your issue. Were it me and my repuation on the line, this would get under my skin, and I'd try to help find where the ponies went. It does sound like he's trying to poo-poo this off. Does he REALLY think that 80hp are hiding in that 200-300 rpm range? Maybe.... but then your power curve/band is WAYYY off. Bottom line.... that ain't gonna happen. It isn't going to "wake up" at 4201rpm and be done at 4501. (I say "4201" because you've been to 4200, and it hasn't stood the bow up yet).

I'm going in circles... & starting to get angry for you. As prev. stated, do some of the diagnostics mentioned & arm yourself with more info to discuss w/ builder.

Do you have a spec sheet of the parts installed you could post? (it would be mostly greek to me, but someone might be able to tell you something).

Good luck!
Jeff

 

[pinecrestwoods]

Re: Prop issue??

Bump.

Bigdave- any updates on your issue?

 

[Bigdave196]

Re: Prop issue??

Jeff, Thank you for the bump and here are the answers so far....

No 600 pound passengers, and the TACH is almost dead on accurate. We used a digital timing light, to verify the tach.

I did talk, kinda poked and prodded a few questions, to the engine builder. I feel wrong to accuse him of any inproper actions. He still claims that the motor was built to a 300HP rating, and I can't argue with him. He has built several engines for me in both gas and diesel and they have performed as expected if not exceeded expectations. He is also a long time accuaintence of the family who has kept his company busy by word of mouth referrals alone. I do not have a spec sheet not do I know which engine kit he installed. I did hear the rumor that a CRANE cam for a 300 HP marine application is worthless, but I have no idea if that was the brand of cam installed. I am starting to think that it might be time to look into a different cam. I just wish I had the time and $$$ to drag the boat 300 miles south to take it to the lake where we have run it for the last 14 years where the base line was produced from years of use.



QC,

I did stop. I feel like I have been chasing a ghost with this. Sand Hollow Lake's (in Utah) elevation is almost 3000' above sea level, and Utah Lake's is 4551' above sea level. The carb has not been re-jetted. We rebuilt the carb when we were chasing this ghost problem and noticed that the motor was running extremely rich, and the fuel puddling up in places that fuel was not supposed to be was a dead give away too.


We have looked into valve adjustment and reverified that they are in perfect adjustment. Im sorry I didn't post that a few posts ago. We first set them with the motor at TDC and then spun it around once to adjust the remainder valves. Then it was reverified with the motor running just to make sure everything was properly adjusted. Valves are not the issue. We are thinking that the cam may be the overall culpret, I just dont wan't to face that reality of having to pull the motor back out and tear it down to replace the cam.

If the rebuild kit was mislabled, I have no idea if the whole kit was or if it was just a single part of the kit. There are way too many varibles that could easily drop HP in a motor kit.
I did not drop down to a 15* prop either. Thought about it, and ruled it out once I sat down and thought about it.

Sorry everyone that I have been offline for the last week, I am Active Duty Army and they keep me rather busy.


HWSIII,

My outdrive is a Merc Alpha1 GEN II is geared to 1.50 to 1. Would a elevation of about 1500' ( from 3000' to 4550') make this kind of performance change? Could elevation really be the whole culpret?

Like I posted in a post earlier, most of my friends are in 26' to 28' Cuddy/Aft Cabs turning 5.7L to Bravo/Volvo outdrives and they are turning closer to 4900+ rpms at WOT. Its sad when your friends mini yachts can blow past you doing 45-50mph when they have 260HP engines.

Thank you for all the help so far. I am still stumped.....

 

[hwsiii]

Re: Prop issue??

Dave, I do not believe that a 1,500 elevation change made that much difference in how the boat runs. But one of the things I did notice is that with only about a 300 RPM difference the aluminum prop changed your prop slip from 27% with the SS to 9% with the aluminum prop, and a 7 MPH speed increase. And those numbers should actually be reversed from that in most cases beacuse of the differences in blade geometry.
My thoughts at this time are that you are possibly not getting enough RPM to get into the new horsepower because of the cam that was installed in the new build.
What I would like you to do is take both props out to the lake and run them from 2,500 RPM to WOT and give me the RPM and speed numbers in 250 RPM increments. I believe there is a good chance that you need to change the drive unit gears to a higher gear ration in order to use your new horsepower.


H