2008 240da 350/300 BIII WOT?

[sam240]

Hello All,

I have a 2008 240da 350/300 BIII with botom paint. My props were stollen early this summer before my first trip to Lake Mead so I had my local Sea Ray dealer order me replacements (asked for identical replacements). Wow, the cost of props these days:smt089. Here is the question, with my old props I remember WOT at about 5200RPM (could be wrong), but with the new props, I am pushing 5400rpm , what should WOT be? I called Merc and they stated WOT should be between 4600-5000 (this seems low). Everything was fine until this last weekend, my smart craft started throwing errors of "excess engine power" at WOT. I then got the same error at 3000rpm. Any help would be appreciated.

Sam

 

[sam240]

In addition, what should top speed be? I can get up to 42mph when trimmed out.

 

[magster65]

I had a 240 5.7 B3 (2.2-1)... and bottom paint. When I bought it it had 20" pitch props. The performance was very similar to what you describe... annoying really. I tried 22's and it was better but the 24's were best. WOT was 46 mph @ 5000 rpm. More importantly it cruised at 30 mph @ 3400. The 20" pitch props only cruised at 25 mph at that rpm...
Go get yourself some 24's too and keep your 20's for when you have 10 people on board and you're towing 4 skiers.
I found lightly used 24" props for $200 online.

 

[Lazy Daze]

5200rpms is your official rating. I wouldn't be surprised that you can get a bit over that. However, why you couldn't do that before, I don't know. Could other things have changed? Bottom condition, maybe a lighter load in the boat, maybe the older props were slightly damaged?

Check on the side of your flame arrestor cover. It has your engine's specs. I have a couple of dealer Merc books that say 5200. Plus, I've got a new 250DA sitting about 30' from me right now that has the 350MAG - says 5200 on the cover.

Sea Ray says that speed should be between 40 and 44 for your set-up, so I would say that everything seems right.

 

[magster65]

Sorry but imho... at near 5400 or so you're over-revving. Your error messages are probably because you're hitting the rev limiter. You need props with more pitch.
The spec says 4800-5200 (it did on my '06), not just "5200". 4800 rpm at wot is not lugging the engine. Prop it to 4800... it will still get on the step quickly and you'll see better speed right across the board by 4-5 mph. You'll also see better fuel economy and a nicer cruise at whatever rpm you like to cruise at... and the messages will stop.
Seriously... I did a bunch of testing with this.
I guess I'm lucky... this is my hobby / sport of almost 30 years now and my best bud's a Merc tech. I have some experience to draw on.
Cheers :smt001

 

[Lazy Daze]

More info needs to be given before we start recommending changing things from what the Merc and Sea Ray engineers have spent years developing and refining.

5200 is his MAX. Yes, 5400 is too much... but how did he get that number? Over trim? Extremely light load? More info, you know?

I guess we disagree on this, but IMO it's best to try and get your engine propped so you have the ability to reach the upper limit of your MAX RPM (with your regular, normal load - the way you'd use your boat most of the time). This gives you the widest RPM range possible to allow for a wider range of conditions and weight in the boat. For those few times that you have a light load, you can control your RPM's with your trim and throttle.

ON EDIT: I forgot to add... I'm surprised the rev limiter wasn't kicking in at 5400. I *think* it's usually set at 100rpms over MAX?

 

[sam240]

Wow, thanks for all the responses, that is a lot of good insight. I took my boat back to the dealership and they are sending my props out to get tuned ( I will pretend like I know what that means). They said it will bring my RPM's down and give me the same or more top speed. I will try to take the boat out this weekend and see how everything works out. I will post as soon as I get a chance.

 

[Lazy Daze]

Wow, thanks for all the responses, that is a lot of good insight. I took my boat back to the dealership and they are sending my props out to get tuned ( I will pretend like I know what that means). They said it will bring my RPM's down and give me the same or more top speed. I will try to take the boat out this weekend and see how everything works out. I will post as soon as I get a chance.

While tuning involves a lot of math and special equipment, it's basically just "reshaping" the metal blades to make them more accurate. Sometimes adding or subtracting pitch. Pitch is, in theory, how far a prop will push a boat for every one revolution. 22" of pitch means 22" of forward movement. It doesn't work out to be exactly 22" of forward movement, though as the prop will "slip" through the water. Note that some slip is actually a good thing.

So, lets say your old props and new props are both labeled 22" (for example). It's possible that these new ones may be "out of tune" and are actually 20" or 21".

 

[magster65]

More info needs to be given before we start recommending changing things from what the Merc and Sea Ray engineers have spent years developing and refining.

Yes but we're just changing props here... not camshafts.

5200 is his MAX. Yes, 5400 is too much... but how did he get that number? Over trim? Extremely light load? More info, you know?

To keep this is perspective, my '06 would lose 100... maybe 150 rpm at the most with a full load compared to a normal load. MPI's respond very well to added 'load'.

I guess we disagree on this, but IMO it's best to try and get your engine propped so you have the ability to reach the upper limit of your MAX RPM (with your regular, normal load - the way you'd use your boat most of the time). This gives you the widest RPM range possible to allow for a wider range of conditions and weight in the boat. For those few times that you have a light load, you can control your RPM's with your trim and throttle.

:thumbsup: Minor disagreement and either set-up will not cause the engine to expire early or explode.

ON EDIT: I forgot to add... I'm surprised the rev limiter wasn't kicking in at 5400. I *think* it's usually set at 100rpms over MAX?

I think 5400 is where the rev limiter is programmed.

 

[magster65]

If I were you, I'd want new props, not "tuned" ones.
That's what you paid for.
"Tuned" as in they were the wrong ones so the bent some more pitch into the blades.
Not to discredit the art of prop repair but props that are changed are the same as "repaired" to me.
It's not a big issue at these speeds but still...