260da 6.2l river run

[magster65]

My 240 had 20" props on it when I got it; 23-25 (+/-) mph cruise and 39-40 (+/-) wot @ 5300... it was awful and I was completely unimpressed. The 240 and 260's are happiest at 30 mph and up. Anything below... say 25 mph and they want to lean and drag the stern... you'll spend all your leisure time playing with your trim tabs. I tried 22" props and it was better so went to a set of 24". 4" more pitch and I can still achieve 5000 rpm. Now my cruise is 32-33 mph @3600 and tops out at 45-46 mph @ 5000 depending on the load of course. This combination is still on plane fairly quickly so I'd try a set of 26" if I came across them but the 24's are probably best all around.
I had another 240 with the 5.0 (like islandhopper's). That boat had 22" props and it cruised at 30 mph @ about 3800 (or close to it) and would see about 40 mph @ 4500 wot.
Beyond the prop issue there's the rpm debate; I participate in the poker runs every year. Speed is the name of the game so I run between 4000 and 4500 rpm all day. There's other people running at 5000 +... all day. I've seen all kinds of engine failures over the years but never a merc mag mpi even though they outnumber all the others. Keep the fluids fresh and look at the guages more often if you're pushing it and you'll probably never have a failure.

 

[tymar99]

deleted by tymar99

 

[tymar99]

Greetings all. Have been monitoring this thread for a bit, and am puzzled by the high RPM conversation. We run a 1999 260DA, 7.4L MPI, B-III with 24" wheels. As Todd/Nehalennia knows, we do a lot of long range cruising into Canada, and usually fully loaded. At 3,000 I am at 23-26 MPH, depending upon sea state, and skimming along on top, burning 11-12 GPH. 4,000 finds us right at 40 MPH (I don't like the burn rate there).

Given the posted comments, it appears that the big block does not have to work as hard to maintain speed and plane.

I commented to the techs at Lake Union Sea Ray one day that I did not put ours up to 4,000 very often as I did not want to break something. The chief mechanic told me that it is good for the engine to run that fast for half an hour or so "occasionally". But I agree with Todd, I think running for hours at a time at 4,000+ would be hard on the system.

However, I just do not understand "plowing" at 3,000. Trimming the outdrive, as well as the tabs, makes a huge difference in planing efficiency. Sucking the outdrive all the way in (down) can create a heck of a bow wake and slow you down.

 

[keets]

I run with my trim tabs up, only drop one a lil to balance boat if needed. I also trim up the outdrive. I guess every boat runs diff. I tested my fuel burn and 3,800 to 4,000 is where I get the best. Alot of diff opinions on this topic so far. But I must say all the advice from people who have a 2005 260da or newer seem to be pretty consistent.

 

[Nehalennia]

Hey Ty,
Glad you made it here finally.
Put your boats information in your signature and others will know what you have.

Hopefully see you again on the water soon, but in the meantime here online.

 

[BobHenry]

Your boat should run on a plane a lot lower than 3500rpm. My wife and I have a 270
sundancer and we are up around 2800 and
cruising. Check your bottom for fouling. Do
you have tabs...make sure they work...and
before every tripchange the oil every four days like someone suggested. That might be a little overboard.
I would check it before a trip, but change it every few weeks, if used everyday...and their
are probably other members who have great suggestions. Listen to them all. Usually you'll find a pretty good consensus.

 

[keets]

Yea, I know to take in all the info. Alot of good info on this site. I will go over all the post on this subject so I can decide how to run the trip. I like all the diff view points. I have read alot of post on how quirky the 2005 or newer 260da is, however I love how it runs. Anyways, I am kinda new to boating so what the heck do I know????? Thats why I ask.

 

[lorenbennett]

my boat wants to fall off plane around 3,500.
I'm very surprised at that number. Is it propped correctly?

however running at 3500 rpms would take me longer to get to my destination so that would increase the overall rpms also.
The RPM's will stay the same, the amount of revolutions will increase but at a much less stressful level

I have the same problem with my 03 260 with 6.2l, it wanting to fall off plane around 3500 also, but I can keep it below 4000. I don't know about yours , but my WOT is 4900-5000. :thumbsup:

 

[tmhudson2]

Don't want hijack the thread but what is the difference between the 6.2MPI and 350MAG???

In terms of engine displacement, the 6.2 is 6.2 liters or 377 cubic inches; the 350 Mag is 5.7 liters or 350 cubic inches. The 6.2 has replaced the 7.4 liter 'big block' in Mercruiser's engine lineup; according to Mercruiser it gives more power for lighter weight. The 7.4 will have more torque, and should swing a larger prop at lower RPMs.

From Mercruiser:

350 MAG MPI Specifications
Propshaft Horsepower: 300 (224 kW)
Displacement (Liter/CID): 5.7L/350
Cylinders: V-8
Bore & Stroke (in/mm): 4.00 x 3.48/101 x 88
Compression Ratio: 9.4:1
Fuel System: MPI
Full Throttle RPM Range: 4600-5000
Ignition Type: Digital
Alternator (amps/watts): 65/917
Length (in/cm): 37/94
Width (in/cm): 29/74
Height (in/cm): 22/56
Weight (lbs/kg) - Alpha: 952/432
Weight (lbs/kg) - Bravo One: 1025/465
Weight (lbs/kg) - Bravo Two: 1037/471
Weight (lbs/kg) - Bravo Three: 1046/475

MX 6.2 MPI Specifications
Propshaft Horsepower: 320 (239 kW)
Displacement (Liter/CID): 6.2L/377
Cylinders: V-8
Bore & Stroke (in/mm): 4.00 x 3.75/101 x 95
Compression Ratio: 9.0:1
Fuel System: MPI
Full Throttle RPM Range: 4800-5200
Ignition Type: Digital
Alternator: 70
Length (in/cm): 37/94
Width (in/cm): 29/74
Height (in/cm): 22/56
Weight (lbs/kg) - Alpha: N/A
Weight (lbs/kg) - Bravo One: 1025/465
Mercathode (Alpha/Bravo): Kit/Standard
Weight (lbs/kg) - Bravo Two: 1037/471
Weight (lbs/kg) - Bravo Three: 1046/475

 

[berth control]

Couple things -

first - it is interesting that the 6.2 has the same bore as the 5.7, longer stroke, and LESS compression ratio? seems like an odd combo. It seems even more odd that the 6.2 with a longer stroke has a higher rpm range, both these kind of fly in the face of what i thought about engine specs. oh well, I'm sure the guys at mercruiser know what they are doing. I remember a couple friends from high school wanted more hp out of their chevy 350s so they used the cylenders rods and crank from a 400 small block in the 350 and you end up with a 383 "stroker" motor. sounds kind of like what mercruiser did here. maybe.

second - it seems like the rpms are too high. with that size boat the motor will have to work to move it, but I still think they are too high, maybe a steeper prop like others suggested. do you have duo props on a bravo? if a single prop maybe the dia. is too small and not grabbin enough water. i would guess just not steep enough though.

 

[dpmulvey]

The engine is propped correctly. The 6.2 is built to run all day between 3900 and 4200 RPM's. It is new school of thought that a lot of folks have a tough time wrapping their arms around. I have new 6.2's in Saint Max and I too start to fall off plane at 3500 RPM's. However, at 3900 to 4000 RPM's she is sweet. You may want to consider stripping the boat out completely and see how she runs. Then look for any water in the hull. I had a 2465 Regal and she cruised nicely with a 5.0 L at 3750 RPM's (5100 WOT) so you should not have any problem with the 6.2.

I am sure there is more in the bilge besides an engine. Do not be afraid to use tabs to get the nose over and keep her there. You may need more tab size. If so, the fix is less than $100.

HTH

 

[84 SR268]

i believe your WOT should be 4400,,,5.7 or 7.4 ??i have the 84 dancer 5.7 alpha,, great ride , but very sluggish with the 5.7 alpha 15X17 prop is common,i use it ,let the bow come up some trim up the drive , but i think that 5200 rpm is way to high,,