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Fuel efficiency - Yamaha SWS II vs OX66 vs HPDI vs 4 stroke

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Fuel efficiency - Yamaha SWS II vs OX66 vs HPDI vs 4 stroke

Old 05-28-2019, 06:47 AM
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Default Fuel efficiency - Yamaha SWS II vs OX66 vs HPDI vs 4 stroke

I am currently running twin 1996 Yamaha 225 Yamaha Saltwater Series II on a 26' boat. It's relatively efficient. 1.5 - 1.8 mpg depending on load @ mid 30 mph, low to mid 60's WOT. That being said I'm still getting sticker shock after these longer runs here in the gulf. I'm used to the east coast where your in 80 ft of water in 25 seconds.

After burning another 60 gallons in a day last week I started an excel sheet to see when the breakeven point on a repower would be. The only thing I need help on is the relative efficiencies between motors.Using my carbed SWS II 225 as a baseline, how much more efficient would the 225 OX66, 200 HPDI and a 200 4 stroke?

Based on some googling it looks like it would be something like 10%, 30% and 50% (all compared to SWS II). Does that seem about right? I don't think I'm going to drop the cash on 4 strokes but if I can find a cheap pair of HPDIs that may be worth looking into.
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Old 05-28-2019, 07:01 AM
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Too many variables to give you straight numbers:

Total weight
Drive gear ratio
Props
Cruise RPMs

The Yami 200s are inline 4 cyliders and will have to work pretty hard to keep your cruise speed that fast.
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Old 05-28-2019, 01:18 PM
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Hpdi and first gen 4 strokes around 25% better at cruise. If you troll, the 4 strokes are better than the hpdi. Later gen 4 strokes better again but not sure you will see 50%
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Old 05-29-2019, 05:28 AM
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Originally Posted by UncleLuke View Post
Too many variables to give you straight numbers:

Total weight
Drive gear ratio
Props
Cruise RPMs

The Yami 200s are inline 4 cyliders and will have to work pretty hard to keep your cruise speed that fast.

I believe I'm around 6200 #s with 25p Quicksilver Mirage props. Google suggests 1.81 final drive ratio but im not sure. I'm not sure what RPM I cruise at but will take a look next time. I'm not a speed demon (hence why I could care less if my WOT speed drops from 63mph) but would like to cruise anywhere in 30-40.
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Old 05-29-2019, 06:24 AM
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Those carbureted two strokes are not very efficient. I had a 1996 SWS-II 250 on my 23' Grady when I bought it and used it for two seasons. I re-powered with a modern direct-injected engine (let's not turn this into a brand war) and my fuel consumption dropped considerably. I didn't have good baseline numbers without a flow rate gauge but I estimated less than 1 mpg. The no-wake zone and idle would also suck down the fuel.

The new engine gets 2.7 mpg at cruise and 8-10 mpg in the no-wake zone. I don't use my boat enough to justify the cost of the re-power with fuel savings but I simply have no regrets.
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Old 05-29-2019, 06:27 AM
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You will not see any significant difference in the carb'd SWS 225's and OX66's. I have run both of these engines in a twin set-up on my 25' Whaler. At low RMP, the OX's shut sown 2 cylinders for a very slight increase in fuel consumption. At cruise, assuming carb's are tuned, again, you may see a very slight increase with the OX's. The OX's seem to tolerate ethanol better than the carb'd SWS though. If you are burning most of your extra fuel at cruise, both the HPDI and 4-stroke will be 25% +/- better.
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Old 05-29-2019, 09:38 AM
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As others have said, need more details to make an informed decision.

My 225 OX66 burns 29 GPH at WOT. At 32 mph - a comfortable cruising speed, I get 2.6 MPG (I have a Lowrance EP-60 connected via N2K to my GPS). Grady's specs show 3.2 mpg for the same boat with an F225. I'd have to burn a lot of fuel to recover the investment based on .6 mpg improvement.
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Old 05-29-2019, 09:49 AM
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Good to hear the HPDI offer a significant jump. I think I will start searching for a good set to upgrade to. How many hours are too many hours?
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