Engine power band

[S-3 Ranch]

Well guys I am ignorant about some mechanical thing like torque importance
What is more important on airboat RPM or low end torque
My build will have a 1:9 to 1 reducer gear and a 30 HP EFI engine , carbon fiber three blade
My old boat had a 300+ HP and was carbureted
Can these new engines be improved with electronic tuning or is that just not important and RPM is the important part
Thanks I hope I made sense

[RifleBowPistol]

Not really sure. What engine are you using now? 30 hp. is not much, sounds like a little two cylinder. EFI probably won't help your hp, but intake design can help power or widen power band and EFI allows for different intake designs, which some can help low end power or widen power bands.

[muzzlebrake]

Tuned exhaust system can help torque immensely
A properly tuned exhaust can help boost or flatten the torque curve prior to 5252 rpm where torque and Hp are the same. After 5252 rpm the torque falls off and HP keeps climbing with rpm increase and the tuned exhaust then helps HP gain by evacuating more exhaust gases helping to pull in more fuel charge. Doesn't matter if its carbed or injected.

[bboswell]

With a 1.9 reduction ratio I doubt you will be able to use all of the engines RPM capability since the prop is likely limited to 2500 RPM.

[S-3 Ranch]

With a 1.9 reduction ratio I doubt you will be able to use all of the engines RPM capability since the prop is likely limited to 2500 RPM.

Yes I was brushing up on my propeller design and the manufacture states that
The propeller was designed for max of 2900 rpm
So the propeller 2900 X 1.9= 5320 rpm on the engine
That seems like max rpm for a engine but have no idea ? the propeller is pitch adjustable

“” Adjust the blade pitch angle to fully load your engine at full throttle up to the engine redline rpm, or 50 to 100 rpm below the engine rpm redline. The propeller becomes, or replaces, the engine's rpm "governor". If for an aircraft, set the maximum full throttle rpm for flying straight and level at your typical cruising altitude upto the engine redline. If for a boat, set prop pitch to limit engine rpm to or just under engine redline rpm when on plane (or as fast as the boat can go) in smooth, calm waters .

Obviously you will need a tachometer connected to your engine. This procedure applies to ALL engines at or just under engine redline rpm turning a propeller to produce maximum possible THRUST per HP””


Updated research data
“”The Kawasaki FD620D engine is capable of producing a maximum 20 horsepower at 3,600 rpm. It can also generate a maximum 32.9 ft.-lb. of torque at 2,200 rpm.””


“”

[S-3 Ranch]

I am amazed the thing I learn about when trying to research about weight/ size to torque thrust ratio

[Kbar]

In my best redneck way of explaining it:
Torque is putting energy to work.
Horsepower is keeping energy working.

There are alot of tradeoff's when building something like this. Chines and splash rails. Weight. 2 blade vs 3 vs 5 blade props. wood vs carbon fiber props. Pitch angle for low speed vs high speed.

I did a bunch of reading when the other post started about DIY boats on here. I have a 48x14 Ouchita thats been sitting and really considered either doing an air boat or a sumped jet drive. I just got too many irons in the fire for projects right now.