Best RPM for 2004 340 DA with 8.1s

[jmunro123]

I am getting ready to take a long trip in our 340 with 8.1s, I was just wondering if anyone has figured out the best RPM for fuel economy? It seems to run well at 3500 RPM but I was wondering what others thoughts are on this? I think the best fuel economy is about 3300 RPM, what are others finding?

 

[Novation]

I've found that range (3300 - 3500 rpm) to be optimal for our usage. I usually cruise at 3400 rpm and burn just under 30 gph.

 

[jimdavi]

do you have V drives?

 

[Hampton]

I've found that range (3300 - 3500 rpm) to be optimal for our usage. I usually cruise at 3400 rpm and burn just under 30 gph.

I agree. I have found that once you're under 1/2 fuel, this thing likes to cruise at a pretty decent clip. We have gotten better economy at 29 mph than back at 25 mph once we're light. That RPM was around 3250 to 3350, if I remember correctly. When heavy, the RPM is a little higher and the speed is around 25 - 26 mph, depending on wind and current.

With lots of canvas up (complete front glass), slow down in a headwind to get better economy, and consider speeding up with a significant tail wind. In a head current, speed up to upper end of your normal cruising range. With a trailing current, slow down to the bottom end of your cruising range. With a good trailing current, shut down and watch the economy go to infinity (literally).

 

[BON DIA]

Reading the question literally...I'd say the best economy with 8.1s would be ~ 1500 rpm. We burn 5 gph (smartcraft) at 1600 & 8 mph on gps for 1.6 mpg. Any speed faster than 10 mph all the way to WOT is less than 1 mpg.

 

[Hampton]

True that, but take it one step further and shut one down and do some math - it gets better!
P.S. Nice boat!

 

[Dirtguy]

Do yourselves a great favor and install a fuel monitor system. It will tell you many things you knew or didn't know about your boat. Don't guess or go by "old wives tales."
Look at real data.

There are alot of options but the Navman seems to be a good choice, cost vs. performance.

Boaters world.com has the best deals.

I have a BBC single w/TRS and installed the F210 in about 1 hour.

DG

 

[Bodkin Creek George]

3300-3400 0n our 340 DA v-Drive 8.1

 

[jmunro123]

I did some testing with our boat a few weeks ago. Based on half full of fuel it seemed that the best range was between 3500 and 3600. I used the GPS and the Smartcraft fuel monitor. I am not really sure how accurate the Smartcraft fuel monitor is however.

 

[Newbie]

I did some testing with our boat a few weeks ago. Based on half full of fuel it seemed that the best range was between 3500 and 3600. I used the GPS and the Smartcraft fuel monitor. I am not really sure how accurate the Smartcraft fuel monitor is however.

It seems to be fairly accurate when the settings are changed to read your speeds by GPS instead of by paddle wheel. You can adjust the settings in the smartcraft to change over at 5mph.
I cant add anything else to the 3300-3500 rpm speed as that seems to be about where its best economy wise. I can say that a fast cruise around 3800 sure does feel good though. A couple weeks ago we were trying to outrun a pretty bad storm and ran inbetween 3700-4100 rpm's for about 15-20 minutes. The 340 starts feeling very light on its hull at those speeds. SB

 

[rmilian340]

I run mine at 3300 rpm most of the time. Seems to be the best fuel economy.

 

[Alex D]

My favorite rpm is 3400 to 3600 running 26 to 30 mph ... actually 3600 is a real smooooooth sweet spot for the 8.1s

 

[Good 2 Go]

I have found 3400 to 3550 to be the best economy, .92 or .95 mpg if I remeber correctly, actually no difference between that range in MPG, 27 to 30 MPH. I used the SmartCraft fuel burn and my daughter doing the math on her cell phone using the GPS speed with ebb tide so zero current.
On another note, I cannot believe that Merc did not program MPG into the SmartCraft system, am I missing something? I have looked everywhere and cannot find MPG on the SmartCraft except for the average for a trip. So much for being smart, pretty lame.
I was wondering if I could hook a FuelScan monitor to the SmartCraft electronic output, anyone tried that?

 

[Chris R]

I agree. I have found that once you're under 1/2 fuel, this thing likes to cruise at a pretty decent clip. We have gotten better economy at 29 mph than back at 25 mph once we're light. That RPM was around 3250 to 3350, if I remember correctly. When heavy, the RPM is a little higher and the speed is around 25 - 26 mph, depending on wind and current.

With lots of canvas up (complete front glass), slow down in a headwind to get better economy, and consider speeding up with a significant tail wind. In a head current, speed up to upper end of your normal cruising range. With a trailing current, slow down to the bottom end of your cruising range. With a good trailing current, shut down and watch the economy go to infinity (literally).

I'm right there with John, 3300-3500. We get some fairly strong currents in Puget Sound; thus, if we are going with the current, we back it down closer to 3200- 3300 and save even more gas. Calm water at slack tide, the boat likes 3450 - 3500. The boat rides in a more bow down postion at this RPM.