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-   -   Difference in fuel usage 350CI -vs- 454CI, worth changing? (http://www.thehulltruth.com/boating-forum/551542-difference-fuel-usage-350ci-vs-454ci-worth-changing.html)

RussH 11-23-2013 02:41 PM

Difference in fuel usage 350CI -vs- 454CI, worth changing?
 
Trying to get an idea of fuel usage between a 260HP 350CI engine compared to a 340HP 454CI engine. Would the larger engine use 20% more fuel, 30%, other?

I am thinking about buying a 27' Sportcraft w/ inboard. It has the larger 454CI engine in it but I can buy a smaller 350CI engine for $1,800 that has recently been rebuilt. The larger engine is going to use more fuel than the smaller engine but would it be worth swapping them out? There is nothing wrong with the 454CI engine, it has about 700 hours on it and has never been rebuilt.

Russ

saltwaters 11-23-2013 07:29 PM

Quote:

Originally Posted by RussH (Post 6191634)
Trying to get an idea of fuel usage between a 260HP 350CI engine compared to a 340HP 454CI engine. Would the larger engine use 20% more fuel, 30%, other?

I am thinking about buying a 27' Sportcraft w/ inboard. It has the larger 454CI engine in it but I can buy a smaller 350CI engine for $1,800 that has recently been rebuilt. The larger engine is going to use more fuel than the smaller engine but would it be worth swapping them out? There is nothing wrong with the 454CI engine, it has about 700 hours on it and has never been rebuilt.

Russ

It all depends on whether the 260 hp engine has enough power to get the boat on plane and run it without the secondaries opening up. The general rule of thumb is a larger engine running at lower rpm will use less fuel than a lower hp engine running at higher rpm.

As Tony at Seaboard says props move boats, engines only turn them. The larger engine will be able to turn a larger prop which should give the same speed at a lower rpm than the smaller engine.

This boat will require the same hp from each engine to move it at a given speed. Since it is a single inboard prop slip is always something to be concerned with. The boat with the smaller prop will slip more and be less efficient.

It looks like I'm steering you to the boat with the larger engine doesn't it?

Take both boats for a seatrial and run them at say 20 kts. Take a look at the rpms. You should hear the secondaries open up on these engines. If they are open at cruise speed, it will use more fuel than if they only run on the primaries. I'd want to cruise at 3000 or less.

Try to determine what the gear ratio and prop that is installed on both boats.

sbsurfer 11-23-2013 08:07 PM

Quote:

Originally Posted by RussH (Post 6191634)
Trying to get an idea of fuel usage between a 260HP 350CI engine compared to a 340HP 454CI engine. Would the larger engine use 20% more fuel, 30%, other?

I am thinking about buying a 27' Sportcraft w/ inboard. It has the larger 454CI engine in it but I can buy a smaller 350CI engine for $1,800 that has recently been rebuilt. The larger engine is going to use more fuel than the smaller engine but would it be worth swapping them out? There is nothing wrong with the 454CI engine, it has about 700 hours on it and has never been rebuilt.

Russ

I think what you'll find is that the smaller 350 will have to spin a much higher rpm to create the same torque the 454 will create at a lower rpm. It's not as much about HP as it is about torque. You might even find you'd be burning more fuel with the smallblock to maintain the same speed as the big block.

firstin 11-23-2013 08:10 PM

i think if you went with the 454 you would wonder why you ever questioned it

RussH 11-23-2013 08:42 PM

Thanks guys, I was leaning towards the 454. The 350 will get the boat up on plane but the 454 will do it much quicker with less power.

billinstuart 11-24-2013 06:10 AM

If it's gotta carb you can optimize your fuel economy with simple tweaking. I increased fuel mileage on my 24' blackfin from 1 to 1-1/2 mpg by simple carb optimizing, efficient flame arrestor, and ignition timing. First and foremost is keeping the secondaries on the carb closed at cruise. Very simple adjustment. Next is optimizing total timing. Forget initial timing settings..make sure you're getting maximum total advance as recommended for your particular engine.

muskamoot 11-24-2013 08:05 AM

Quote:

Originally Posted by RussH (Post 6191634)
Trying to get an idea of fuel usage between a 260HP 350CI engine compared to a 340HP 454CI engine. Would the larger engine use 20% more fuel, 30%, other?

I am thinking about buying a 27' Sportcraft w/ inboard. It has the larger 454CI engine in it but I can buy a smaller 350CI engine for $1,800 that has recently been rebuilt. The larger engine is going to use more fuel than the smaller engine but would it be worth swapping them out? There is nothing wrong with the 454CI engine, it has about 700 hours on it and has never been rebuilt.

Russ

You are thinking too much.Run the boat as is with the 454.It's in there for a reason.Swapping to a smaller engine is ridiculous as well as expensive,not everything will swap over.That Sportcraft is a fat pig that needs a big motor.

Shift Work 11-24-2013 08:05 AM

You said there is nothing wrong with the 454 that's in it? Why would you even think about replacing it? Run it till it dies and than replace it with a modern small block with fuel injection that will run circles around the 454 in HP, Tourque and fuel efficiency.


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