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waterthunder gear box ratio ?


Well-known member
with your famous slogan being use it as a torque multiplier not an rpm enabler id like to get your opinion on a ratio setup i designed my sbc 350 to be a dd engine but if i re degree my cam for a higher rpm application {go some what negative instead of positive } i can get more upper rpms out of it my engine combo can safely turn 6500 rpm but that's going to be pushing the reliable factor and i feel safe with saying it can turn my sbc 4500 rpm constant as in cruising across the lake and still have a reliable boat id like to know what prop and box would work best i have 11.5 laser hull setup and i got it as light as possible boat runs great but i know there is alot more power / push to get from my engine it makes really good power as im running my neighbors old 0520 wood prop 78/32 wide blade and can sling it into my msd 3100 rpm rev limiter also i hear alot about p/s props but i have really had a good relationship with the boys at sensinich they have really done a bunch for us boys in the kissimmee area thanks
If you have to turn your motor 4500 just cruising then you don't have enough prop.

What Thunder is saying in his sig is that your gear box lets you do more work by turning a much bigger prop at lower RPM. The result is a lot of push and snap without much sound and that is a great thing for us airboaters.

Think of it like putting 5.13 gears in your mud truck. You don't do that so you can spin your motor 7500 RPM with the stock 31" tires on it, you do it so it can turn 42"s. 8)
i want to cut down on sound and run dry gound real good i dont want to be beating on it just to cross a pasture plus my torque curve is at its greatest point at 4500 and it really falls off after 5800 so i want alot of prop at low rpms but i dont want to be killing the pedal just wanted some input on high ratio 2.68 and 2.37 boxes on sbc and the props that people are running and an idea of there cruise rpm and what it takes to run the hill i would like to run a super wide 2 blade or wone of those cypress series prop and try to really add alot of pitch to get push and how much more efficant it will be when i add more redution over 2.1 more torque = more pitch but will the prop be eficant if it turn slower then 2100 and i add pitch to keep rpm down and im rambling on and on but theres not alot of boys in town running big ratios boxes
Spooled up; I and thunder will disagree on some things ... lets say ... the details . But we agree on using a box to get the torque multiplied.

I never turn my engine beyond 4900 rpms I swing a 84" sensenitch super wide 3 blade and I am past the third mark. I wanted an acceptable amount of push and a very low sound signature. I use a 3.12 box from stinger. my boat is a 15 x8 alumitech with a double wide front deck a full grass rake 12" walkboards. My boat is heavy. I have torque roll yepper I do. I am on plane in about 50' and I feel I can run dry with most folks easily enough. I am not the baddest ground runner but I get by just fine for the first mile or two.

My engine was designed to get all its stuff in a row at or below 5000 rpms.

Hope this helps, I don't know what you did to your motor or where its power curve is but thats my story about mine.
I can attest, CNTRY's boat will run the hill. We ran it on hard ground for what I would say was more than a mile or two. The dew was on the ground, so that helped, but we were haulin' butt! With 3 people on board too. He was feathering the throttle most of the way.

All the sound that comes from the boat is a pronounced "Whooshhh" and the normal whine from the gearbox. I would say the box is probably louder than the prop is and it's not that loud.

Gear reduction WORKS.