Prop change to improve fuel useage?
If a person isn't concered with top speed or holeshots and would rather have improved MPG, what kind of prop would a person look at changing to?
My intial guess would be change the ratio in the outdrive and match it to a prop. I am sure that would loose top end speed but might allow the engine to turn less rpms with more load. Letting the engine torque work instead of RPMs. But if a person just stayed with stock gearing what should a person look for with prop selection? |
Re: Prop change to improve fuel useage?
Hi ryker137, if your looking for just MPG, I recommend sticking with the stock prop. I find that in most circumstances, the factory prop gives a good balance between takeoff, top end and overall cruising. You want a prop that allows the motor to achieve the listed max RPM at WOT.
I suggest you try waxing the hull (less friction) and keeping the boat weight down and trimmed properly if you're looking for a few more MPG, these three things go a long way to helping get every last mile out of a gallon of gas. I suggest you contact Mercruiser to find out at what RPM your motor makes the best mileage, and then you can determine whether you need to spend any money to squeeze out a few more MPG. Since boats typically rely on engine RPM alone to determine speed (no multi-gear transmission), the question is: At the best MPG, how fast do you want to go? This may determine what you will need or can do to achieve that speed. Good luck, WetWilly |
Re: Prop change to improve fuel useage?
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If changing the gear out isn't that costly or labor intense - dropping down to the 1.47 ratio like the v8's have would be nice for top end and perhaps MPG or GPH. The 4.3l v6 is the same engine thats sold in S-10 trucks. So there are high performance intakes, camshafts, and carbs that would allow the 4.3l to make almost as much torque in the upper RPMs as the weaker tuned 5.0l v8. I've seen 4.3l trucks with 220hp - 240hp. My overall speed would be average slighly over plane out - since that nets the best MPG in most cases. But it would be nice to outrun the rain o make a beeline to the restroom (for the wife). |
Re: Prop change to improve fuel useage?
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Years and years ago I owned a little Yamaha Twin One Hundred motorcycle. It was under-torqued, IMO. So I dropped the gearing a bit. Not much. Just a few teeth. Not only did my low-end torque improve, my top end improved even more! Quote:
Jim |
Re: Prop change to improve fuel useage?
ICE operates at its most efficiency when under larger loads. Keeping that throttle body open and decreasing pumping losses while turning as few RPMS as possible. Which is why the 6.0l Corvette gets better MPG than a 2.0l Honda S2000.
correct? The torque curve for the 4.3l is terrible for anything past 3500rpms. A better camshaft profile and intake design will offer a more flat torque band up to redline. With camshaft and intake there can be a 20+ft/lb gain over the stock profile at 3500+ rpms. I think the stock Mercruiser uses a single plane intake, so going to a double plane intake design is a huge improvement in top end torque. |
Re: Prop change to improve fuel useage?
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Nonetheless, it looks like you've researched it more thoroughly than I. Jim |
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