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Honda powered airboat

Guys I’m new to airboats and have lots of questions concerning my build and hope you can help as they arise.
A little about my build- the haul is a 12’ sled not sure who it’s built by as it’s a homemade title. Engine is a Honda k24 built turbo engine it dyno at 1003hp 889tq at 8800rpm On E85. I’m running an adapter plate for LS trans as the reduction boxes available for the engine are only good for 250hp. So my question is what gearboxes do you guys recommend what reduction and prop combination should I go with? I will post pictures of the build in the next few days, thanks in advance.
Very interesting. What power is it making at 5500 and 6800 rpm? I believe ox-box makes a 2.88 ratio. Each manufacture offers a similar but different lineup of gear options. I didn't realize anyone was making a 3.26 ratio. I would check them all out and see what's currently available.


I encourage you to start a build thread, I would love to follow along. The Honda K motors have always impressed me. Post the dyno curve. That will give guys a better idea of what rpm range you may want to target. Also need to see what is the max diameter prop you can swing on your hull/cage. You will likely select the highest ratio gear offered by the box manufacture you choose but maybe not.

And OX-BOX are great people to deal with. I bought two last year for projects.

Also what are your goals for the boat?

Good luck!
I still can’t believe your going to do that to a K motor. By far the best motor Honda has put out and clearly you know the motor by your HP your already making with it. I’m sure you e figured out you can make that power a lot cheaper with many different motors but you will absolutely have a one of a kind … interested to see this build
Something to keep an eye on with low displacement high rpm engines is the required power curve of your propeller of choice vs the power curve of your engine.

Most engine combinations have sufficient power at low to mid rpm to power a prop through that region.

However, if your power curve is such that it remains very low until an elevated RPM and then spikes up quickly at the last 2000 rpm, you may find that even though you make enough power on a dyno to swing a certain propeller that in practice on an actual boat that your engine lacks enough mid range power and it will effectively stall at whatever point in the rpm curve that the power the prop needs to increase in rpm is equal to the engines max power at that lower rpm.

This is very easy to see if you plot the propeller required power curve vs rpm and compare it to the engines power curve vs rpm. If the prop exceeds the engines curve at any point below max power, the prop will stall the engine at that lower power level.

So, something to keep in mind. I would be cautious about running wide props on that type of engine. May be doable, just going to depend on your actual engine power curve.
Why not stick a aircraft engine on that and learn how much fun you can have. Putting a motor like you have on that is like learning how to drive your first time in a drag racing car. I will say I know nothing about that motor but the HP and torque numbers are over the top. OneBFC probably has some valid points. Props are limited on RPM’s so the gear box and prop would be massive for a boat that size.
Sabers are rated up to 1000hp & 3000rpm max, so 10 or 12 blades may hold it at wot. I agree with blackcoffee's comments!
Thanks for the advice guys, what I may do is step down in turbo size to bring in boost sooner. It’s has a gt4202 on it now i will call precision turbo see what they recommend for up to the 6800 rpm range. The goal is to stick with the k-series Honda engine and figure it out. Engines are a dime a dozen, parts are all over the place, they are light 254lbs without turbo on my scale and cheap to make good power.
I just saw someone else on another platform start building one with a K series and I don’t think these 2 guys are the same but I could be wrong. The one I know of on another platform will absolutely make it work at all cost. Maybe I can get him to add a build thread over here
I seen I believe boosted boys are building a k24 and they are using a gearbox ordered from overseas and are running a rotax hub they are gonna have issues with the hull design but here is a link to their last post about

K24 airboat
Yes sir that was the one I was referring to. It may not be what we all think of parts wise or how some would set it up but they have the backing to make what they said they would and they have. Would be interesting if you could get the combo right and I would almost go as far as saying fairly inexpensive.