4 cyl. Outrigger Hydro


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I will throw one out there for ya.........

Was tossing around a HP rotary valve 4 stroke .21 or the .25 with a RB Innovations supercharger on it. should be good to 15000RPM.

Thy also have a .49 size eng.

I have not seen the inside of one .But I bet with a little grinding on the rotary valve you can change the valve timing pretty easy.

If you are going to go out side the box. Why not go all the way.

Bet that would be one sweet sounding eng with the supercharger spooled up.

Don't know if the eng will handle it but only one way to find out.
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I'd be shocked if the RB innovations supercharger would make a difference. In the small sizes we are talking about, centrifugal blowers are very inefficient. The smallest turbocharger I know the specs on is the Garret GT0632TZ. The INI RHB31 may be a little smaller. The smallest two stroke it is suitable for is around 60 cc. A four stroke would need around double that. Positive displacement blowers work better in small sizes. They also can run at the engines rpm. That means piston, vane, or screw compressors. OS ran a positive displacement blower on an engine years ago, but the YS piston supercharger was better.

Lohring Miller
Don't know how much thy put out. But thy are sized for a .34 2 stroke eng. A 4 stroke only intakes every other revolution. So the sizing would add up twice as fast. Don't think you would want to much boost on this eng to start with. Would be cool to give it a try.

With the rotary vale the timing changes would be a snap to do. Not so much on a OHV eng.

Heck the HP .21 is only $199 and the RB charger is about $150. Not to much investment to give it a try.

Just a little cobbling and you would have a 1 of a kind set up.

The COOL FACTOR would be over the top.

That is the whole point of it is it not?
Yes on a 2 stroke it is. But on a 4 stroke????????

Has any one ever seen one in person and spinned one up with a Dremel tool?????
Because if you hook it on a Dremel you can spin it up to speed and hook a hose to the out put side.

Then hook the hose to a pressure gauge and see what it can produce in PSI.

I spent many days as a kid taking radios apart..................LOL

The BOX is very small I see........................
Here are some pics of the finished rigger and a vid attempt at the local club.


Published on Jun 10, 2017
First launch with the Saito .30
Octura 1637 prop.
Unloading after the launch up to 15,665 rpm prop was too small, not enough thrust.
Left out and got up to 31 mph then fades off and completely bogs down after the turn.

I want to run pure three point with no additional prop support advantages.

Need perhaps 40mm to 45mm dia. range to keep the thrust up. It is odd you have to retrain the ears

to low rpm and focus on the engine's torque for the right prop. Will take some time to find what works

best I have 6 different sizes that may be within suitable range ready for testing next time out. The engine

has a no load rpm a bit rich at 16,795 given the engine ran up to 15,665 on the water I was clearly under propped.

Jim from another site used a 45mm prop on the .30 size Surpass with his mono providing good sport

running results going from idle to full throttle with no prop cavitation. So the quest continues will post

another vid soon as possible doing some laps next time



Total weight less fuel 2.136 Lbs.
Total length of the wood hull is 33.5" and 36.5" to the prop nut.

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Update on the saga of ye ole 4 stroke efforts.

Swapped the Saito .30 out never got to test with the right prop needed at least 3in total pitch

to take advantage of the torque. Installed a fresh out of the box O.S. FSa .56 Alpha this new

version has no crank case breather nipple for excess oil, rather runs it up through the cam, up

the rod tubes into the rocker arm box and weeps out a small port to mix with the exhaust valve / chamber.

The transfer of the oil under pressure seems to be helping with the cooling. I did a brief break in

on the bench then ran a rich run at the local club just in the nick of time as a storm was approaching

lightening within 3 had me cautious but anxious to get this cursory run over.

I put a Prather 220 on which was the only real choice I had unfortunately it is too small to make

any speed with a mere 2.6" of total pitch ok for .25 size engines. Good enough for a break in run all be it a bit

pathetic. Top speed was a scant 32 mph best pass as the engine cooled the speed dropped. A storm was coming

in the air went from 95F down to 76F from the time I had set the NV on site to actually running it. The engine

as you can imagine went very rich as it cooled down further during the run.

I have 3 props in the mail from what I learned the rpm did not change from bench to loaded state on the water.

The meager prop load did not phase the engine rpm. Started at 15.4k by the time I ran out of fuel it was down 800rpm

due to cooler air from the front and just moving along rather than static on the when the NV was set on the table.

4 strokes need to be set a bit lean on the bench to compensate for cooling once on the water. All the same this

was a break in run so no harm no foul I was 5 clicks rich on the bench for the break in run. It is all I can show till

the new props come in. I must say the Alpha series with a low end NV ticks over nice with a OS .45 size flywheel.

I will try 3.75" / 4.14" and 4.334" total pitch props. I figure the torque of the Alpha .56 4 stroke is around a .65 - .70 2 stroke.

Of course this is all new ground and gut feeling less science. Potential unknown est. around 50 - 60 mph is possible

with the right prop. Would be nice if ABC props would load their distributors up with some stock

For now in the mail:

- ABC S-20 55mm

- ABC 2318

- Octura 2250

The engine will hold 16.2k with no fuss. Look forward to posting further results with these

props should expect a big jump in speed. Unique 4 stroke sound which wont change tone much

as the torque sync's up with the right prop. So here is a vid for now and a few pics. Sun was not

ideal for still shots from the vid but clearly shows the ride attitude during this break in run.

3.1 lbs less fuel. 3ft ply skinned balsa sponsons, ply tub. 7mm x 5mm carbon tubes, bare

strut no ramp in the back / no need plenty of torque the engine only strained at the end

looking for the last drops of fuel. 19% oil 45% nitro. Next vid perhaps this weekend if the

new props show up.





What propellers do you need?

If you are going to run the Old Legend Series from ABC I still have plenty of them in stock.

I can always order what anyone wants from ABC. The tough part being a propeller

dealer for over 17 years is figuring out what people need or want. With 10,000+

R/C boaters all over the world it is tough to keep in stock what everyone wants.

Let Me Know If I Can Help You?

Mark Sholund
Thank you Mark, I bought what was available that should start to load the engine.

I really don't know what size yet treading new ground here.

One advantage with 4 strokes they run big props which will improve slip percentages

perhaps 10-12% can be realized. Will radar and monitor the rpm to compare.

Square aspect ratio's may be the trend such as a modified prop to 2121 with generous

rake and a low bar number.
3 of the props came in the mail: 50mm, 55mm, 58.42mm

The 50mm looks like a good fit for a 3ft rigger the 55 seems to be near the limits with it's blade area.

Will test the Octura 2250 and ABC S-20 (1655) it's what I could dig up in a pinch and two ends of the

spectrum to oust out what direction to go next.

The 58.42 is so proportionally up sized seems to be out of range and needs to be cut to reduce the

over all bar down from 50 to perhaps as much as 35 to retain the top end rpm.

With 4 stroke's it's an interesting challenge, they sound good and efficient with valves

boosting torque / unique change from my last 2 stroke rigger project.

Pic with the ABC S-20 makes the hardware look adequate rather than beefy.

ABC SK 2120-23-36 if existed would be a much better direction for the FSa .56



Your rudder is pretty short for those lifting propellers.

Do you not sharpen and balance your propellers first

before you try them? Look into some of the three blades

in the ABC lineup, I think you will find a winner.

The ABC 2221-19-38% would be too much propeller for

that set up I think? Why not look at a 2115/3?


Mark Sholund
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Good morning Mark,

Just the angle of the pic here is a better view, yes always prep all prop brands.

I looked at the 3 blade props, need a few runs with reasonable load on the engine

to get a better idea. Last weekend I was only able to manage a break in run with small

prop before the storm came in shutting down the day. Will post another vid with the

best new prop on hand now. Thank you for your input, much appreciated.


If you index your propeller at 6' o'clock you want the bottom of the rudder blade

3/4" down from the bottom of the propeller blade. Looks like an old Octura paddle wheel

on their now? I may have just the ticket for your application. I need your address please?


Mark Sholund
I have 1.2" of rudder below the the Octura 2250 lower blade,

will vid the vintage wonder if it does not prop walk in a circle lol.

Last night I spent over an hour dressing it up for a run.

What prop are you thinking Mark?

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