WOT rpm lower vs engine damage?

Creekwood said:
Sounds like you are on track. The only other thought is to make sure that you consider what happens when you fully load the boat. If you are testing with a lighter than normal load (less than the normal number of people for example) then you probably want to get to the top end of your WOT range so when you load it up it comes down in the range and not below.
Click to expand...
I have thought of that. I usually don't overload her.
Pretty much how I tested is how I use it.
Good point. Thank you
 
gtfireftr said:
I will try to explain it better........
I initially started with a 19p 3 blade vengeance prop....the performance was lackluster at best....
Purchased a 4 blade 18p, which by all accounts overloads the engines..... hole shot was much better, cruise faster at a lower rpm... but could only get 4100 WOT.
I was sent a 16p, 4 blade.... this allowed me to reach 4700-4800 WOT, but cruise at a higher rpm.....
This is why I said I thought the 17p is in the middle and perhaps what I need.....
The reason I went down in rpm, AND had a better holeshot was I had a tremendous amount of prop slip with the original 3 blade props...
Sorry for the confusion.... Thanks for the info
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OK, that's making more sense. You said "prop slip"... were those "hubbed" props? That would ABSOLUTELY account for the performance issues. Just putting a good set of 19" (or possibly the original 21", depending on your average boat load) might be a good idea, too. To compare performance to defective props isn't a good comparison. Also, you should definitely be using your tabs - they are a great tool to help with many things, not just hole shot. And, what kind of MAX speeds are you seeing (ideally from GPS)? I don't have a book in front of me, but I would estimate that you would see somewhere around 40MPH the way Sea Ray originally spec'd the boat.
 
Lazy....
The 3 blaades I took off have hubs.
I am not sure if my top speed at WOT. I am going to test it today with the 16p.
I am almost sure that it's not near 40 though. I will let you know later this afternoon.
Thanks for the info
 
Sorry, I wanted to add something else but had to go take care of a new puppy "issue"...

While I understand what you meant by the various props you're playing with, there's still something that's amiss. The stock props (21") would have gotten the RPM's into the proper max rpm range. Since you have gone DOWN in pitch, your RPM should have gone up - not compared to the 3-blades you had on there since they may have been bad, but compared to GOOD 21" props. If the engines are healthy, drivetrain is good, running a normal load in the boat and the bottom is clean, your max RPM should WAY above the 4600/4800 mark, not below, with the 18" or 16" 4-blades.
 
I really don't know to be truthful.
I never had 21p on her. These number are real. Gps speed etc.
i can tell you that prop slip was a real issue. According to Mercure Prop slip calculator i had about 30%. This translates into a "slipping clutch, or transmission"
 
I have re-powered my Sea Ray Sundancer 260 from a 7.4 to the new 6.2. I went from 24 pitch prop to a 22 pitch one but I am still only getting 4200 at WOT. Merc says I need to get into the 4,800 to 5,200 range. I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

I believe the gearing on the Bravo III is 1:2.0. My mechanic says I can try a 18 pitch prop (Hill Marine offers one) but if that doesn't do it I will have to re-gear.

I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

Any advice?
 
jgyatesjr said:
I have re-powered my Sea Ray Sundancer 260 from a 7.4 to the new 6.2. I went from 24 pitch prop to a 22 pitch one but I am still only getting 4200 at WOT. Merc says I need to get into the 4,800 to 5,200 range. I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

I believe the gearing on the Bravo III is 1:2.0. My mechanic says I can try a 18 pitch prop (Hill Marine offers one) but if that doesn't do it I will have to re-gear.

I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

Any advice?
Click to expand...

you should eliminate all the things that can cause the engine rpm's to be lower than expected before spending money on a new prop and/or new gears...I hit 5,000 rpm's with both of my 6.2's this past WE on a quick WOT test run....they are sweet running engines....I then cruised on plane at 4,000 rpm's at 25 mph for about another 30 mins. and the engines were not straining at all.....

things to check include:

1. is the engine performing as expected?.....don't assume so just because it is new...
2. is the gas fresh
3. is the gas ethanol free?
4. is the hull bottom clean?
5. are the trim tabs fully retracted?
6. is all canvas either removed from the boat or in the 'down' position?
7. is the fresh water tank empty?
8. is there a minimal amount of fuel in the tank?
9. are there any others on board with you?
10. is there a lot of weight from 'stuff' on board?
11. was the outdrive properly trimmed for optimal performance?

good luck...

cliff
 
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jgyatesjr said:
I have re-powered my Sea Ray Sundancer 260 from a 7.4 to the new 6.2. I went from 24 pitch prop to a 22 pitch one but I am still only getting 4200 at WOT. Merc says I need to get into the 4,800 to 5,200 range. I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

I believe the gearing on the Bravo III is 1:2.0. My mechanic says I can try a 18 pitch prop (Hill Marine offers one) but if that doesn't do it I will have to re-gear.

I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

You say "still only getting 4200 at WOT"
Was the 7.4 the same?
You can try other pitch props as well as the 18p....... I went through 4 sets in order to get what I wanted....
pm me and I will put you in touch with the prop guy I used....
Click to expand...
 
FireFighter - did you ever get your issue resolved?
 
Lazy Daze said:
FireFighter - did you ever get your issue resolved?
Click to expand...
I did I believe.
After much trial and error I ended up with a set of props that put me in the Sea Ray specs for WOT, and allowed me a decent cruising speed.

Thanks for all the advice.
 
OK, good to hear. Keep in mind that if they're much less than the originally spec'd props that there's still likely something else going on - possibly the engines are low on power, for example. So, keep an eye on things as "band aids" don't usually work in the long term - they only cover up a problem until it gets worse. Often times, it then ends up being worse than it would have been by fixing the problem to begin with.
 
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Lazy Daze said:
OK, good to hear. Keep in mind that if they're much less than the originally spec'd props that there's still likely something else going on - possibly the engines are low on power, for example. So, keep an eye on things as "band aids" don't usually work in the long term - they only cover up a problem until it gets worse. Often times, it then ends up being worse than it would have been by fixing the problem to begin with.
Click to expand...
Thanks for the input.....I think that the props were an issue right from Searay..... I can reach WOT on both engines, and she seems to be very happy cruising at 3400-3700 rpm....... Hopefully there are no underlying issues......
 
gtfireftr said:
jgyatesjr said:
I have re-powered my Sea Ray Sundancer 260 from a 7.4 to the new 6.2. I went from 24 pitch prop to a 22 pitch one but I am still only getting 4200 at WOT. Merc says I need to get into the 4,800 to 5,200 range. I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

I believe the gearing on the Bravo III is 1:2.0. My mechanic says I can try a 18 pitch prop (Hill Marine offers one) but if that doesn't do it I will have to re-gear.

I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

You say "still only getting 4200 at WOT"
Was the 7.4 the same?
You can try other pitch props as well as the 18p....... I went through 4 sets in order to get what I wanted....
pm me and I will put you in touch with the prop guy I used....
Click to expand...

Honestly, I never took the 7.4 to WOT. I bought it used and it was "stock" and I assumed all was good.
Click to expand...
 
CliffA said:
you should eliminate all the things that can cause the engine rpm's to be lower than expected before spending money on a new prop and/or new gears...I hit 5,000 rpm's with both of my 6.2's this past WE on a quick WOT test run....they are sweet running engines....I then cruised on plane at 4,000 rpm's at 25 mph for about another 30 mins. and the engines were not straining at all.....

things to check include:

1. is the engine performing as expected?.....don't assume so just because it is new...
2. is the gas fresh
3. is the gas ethanol free?
4. is the hull bottom clean?
5. are the trim tabs fully retracted?
6. is all canvas either removed from the boat or in the 'down' position?
7. is the fresh water tank empty?
8. is there a minimal amount of fuel in the tank?
9. are there any others on board with you?
10. is there a lot of weight from 'stuff' on board?
11. was the outdrive properly trimmed for optimal performance?

good luck...

cliff
Click to expand...

Love the check list! Yes engine seems fine, have half tank of new fuel with ethanol, been in water 4 months so not too clean, I will ck trim tabs, canvas was up, lots of stuff, no others but me. Despite all these less than ideal conditions, I don't think they would result in a 1,000 rpm below the top of 4,800 to 5,200 WOT range for this engine. I got good price on Hill props with rebate of my 24's. Worth a try! I will do as you suggest after prop change! Hopefully I will be at 4,800 which should be ok with all my "poor" testing condition.
 
jgyatesjr said:
been in water 4 months so not too clean......Despite all these less than ideal conditions, I don't think they would result in a 1,000 rpm below the top of 4,800 to 5,200 WOT range for this engine....
Click to expand...

you may be surprised how much a dirty hull can affect the performance....

cliff
 
jgyatesjr said:
I have re-powered my Sea Ray Sundancer 260 from a 7.4 to the new 6.2. I went from 24 pitch prop to a 22 pitch one but I am still only getting 4200 at WOT. Merc says I need to get into the 4,800 to 5,200 range. I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

I believe the gearing on the Bravo III is 1:2.0. My mechanic says I can try a 18 pitch prop (Hill Marine offers one) but if that doesn't do it I will have to re-gear.

I only have 20 hours or so on new engine and all low use - no extended runs over 20 mins.

Any advice?
Click to expand...



The 6.2s need to run on Gas without (the 10%) Alcohol in it and 91 Octane or Better
10% Alcohol runs hotter and diminishes performance up to and over 10%
AND With Alcohol it IS possible to melt pistons
454s don't care much what ya run in em:huh:
 
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I have a new 6.2 in a 1999 Sea Ray 260 Sundancer and the engine has failed. It has only 36 hours on it and I have babied it since it was installed last September 2014 only going over 4,000 after 20 hours I was running 22 pitch props but only did 4200 RPM at WOT so switched to 18 pitch Hill 4 blade Signature props. On the first test run, I got it got to 4,800 but then engine lost power. There were no alarms. When I put in neutral it died. When I got it restarted, it was missing terribly so cut it off and got tow to slip. I called Mercruiser and they said have local Mecruiser dealer ck it out. He quickly determined that there was no compression in two cylinders and low is the next one, all on the right side. The plug electrodes were gone in the cylinder with no compression. This seems un-real to me. Engine goes bad in first 36 hours! Anyone have similar issue with 6.2?
 
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