340 (496) 8.1 RPM range with props?

So as some of you know I'm always looking for more speed. A few years ago I had my props re-pitched because I was above my WOT range of 4200-4600. I was at 4730 so I ended up going from a 18x21 with a .075 cup to a 18x22 with a .075 cup. After that I was at 4620 for some reason and gained like 3mph. So last year I had them go over the props again and add a .125 cup. My speed right now is 28 to 28.5 mph at 3450rpm and a WOT of 38.5 at 4560rpm. I called ACME props and talked to him for a while. He suggested there 18x23 with a .043 cup. He told me it would gain around 1 mph on the top end at 4450rpm and .75 at cruise. Well if you do the math, there is no way i'm spending $3500 for that. So I'm thinking...safe RPM range is 4200-4600. What's stopping me to add another 3/4 or so pitch in my prop. I would drop like 150 rpm bringing me to around 4400 rpm. I should gain better mph at cruise. I know optimal rpm is 4600, but if the range is 4200 to 4600 I should be good, right?

1/4 fuel with no water or waste and 2 people would be what you want at 4600 imo. Adding to much pitch may cause you to lug the engines under certain conditions. I would not prop to max out in the lower end of the range. Are your plugs and wires fresh? I get 50-100 rpm everytime I change. A lot depends on how clean the bottom is. I always do a speed run out of the gate in the spring for a baseline. Current, weather and waves play a big part too. The numbers you show look pretty respectable to me. I've see folks hit 40 with 18x23 .5 pitch. So I think the Acme guy is accurate. I think your set up is better suited for cruise than speed. I always work under the premise that less pitch = more speed less cruise.

Different hull with my boat (beamier/heavier), but same engines. Swinging the OEM Hytorque's 18x21 (can't recall the cup) and WOT 38.5MPH @ 4500RPM is the best I've ever gotten with a clean bottom and the wind at my back! Had them done at Wolverine Propeller 10yrs ago...

Like you, I think there should be more speed but I'm not sure the cost of new props would have a decent break even point.

Jimmy Buoy said:

Different hull with my boat (beamier/heavier), but same engines. Swinging the OEM Hytorque's 18x21 (can't recall the cup) and WOT 38.5MPH @ 4500RPM is the best I've ever gotten with a clean bottom and the wind at my back! Had them done at Wolverine Propeller 10yrs ago...

Like you, I think there should be more speed but I'm not sure the cost of new props would have a decent break even point.

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I could get a added pitch size for like $500. New props are out of the picture. My RPM will be at around 4400 after. I'm not sure how my MPG would work out either.

Craig said:

1/4 fuel with no water or waste and 2 people would be what you want at 4600 imo. Adding to much pitch may cause you to lug the engines under certain conditions. I would not prop to max out in the lower end of the range. Are your plugs and wires fresh? I get 50-100 rpm everytime I change. A lot depends on how clean the bottom is. I always do a speed run out of the gate in the spring for a baseline. Current, weather and waves play a big part too. The numbers you show look pretty respectable to me. I've see folks hit 40 with 18x23 .5 pitch. So I think the Acme guy is accurate. I think your set up is better suited for cruise than speed. I always work under the premise that less pitch = more speed less cruise.

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Thanks. Here's my thing... Plugs are changed every other year, wires are new, Bottom is always smooth and clean, fuel filters changed every year and use Stabil and startron at every fill up. At the end of this season I was able to hit 4580 rpm at 38.5 mph with 8 people and 3/4 of gas. Cruise at 28 at 3450rpm. I don't always do WOT, so i really don't know what 2 people and 1/4 tank would do. I would assume over 4600.