Dyno numbers
 

Guys, let me try to clear this up...

My dyno is an inertia accelerometer or inertia dyno. When I designed it I used industry proven formulas to calculate the flywheels moment of inertia. These formulas can calculate how much torque is required to accelerate any given inertia to a specified speed in a specified time. I used actual torque output figures from current engines to determine the approximate flywheel inertia and therefore flywheel size. I have verified my flywheel moment of inertia using online industry inertia calculators. My flywheel is 99.9% accurate to test engines of this size. The numbers I calculated suggested it should take 10 seconds to accelerate my flywheel inertia to 40,000 applying .15 ft. lbs. average torque. Turns out my dyno takes 10.3 seconds. The dyno is 99.9% accurate as long as the software knows EXACTLY how much inertia I am accelerating. This is very important to accuracy.

As far as RCCA's so called dyno is concerned I hear the dyno they had made never worked properly and they are back to using airplane props to determine TQ output.

Well, in my opinion that doesn't work. Airplane propellers aren't designed to run in a stationary position. The number of variables is to great. First, propellers cut thru air, the path they take is sort of like the threads of a bolt. Spiraling thru the air, cuting thru and forcing itself forward at the rate of it's pitch. If you hold a prop stationary and raise it's rpm, it quickly overcomes the rate of air flow it can draw thru it's blades and succombs to prop wash. While in motion, each prop blade always encounters clean air. An example of propwash is similar to a jetboats impeller cavitating. In the boats example cavitation occurs when the impeller sucks air and cannot force water in or out. In the airplane propellers case each blade of the prop is stuck in the wash of the previous blade and it's effect to push air is reduced dramatically.

Secondly, any propellers effectiveness is dependent on the relative air's density, or it's concentration of molocules. Thin air is much easier to compress than thick air. Barometric air pressure is always changing. This is similar to your car running at sea level and your car running at 5000 ft. There is a huge difference in the amount of compression at sea level and at 5000 ft.

There are formulas to calculate how much tq is required to turn a given propeller at a given rpm, however this requires the propeller to be turning itself thru clean unspoiled air in a cork screw pattern. By holding the propeller from moving thru the air all these formulas go straight out the window, therefore rendering any accurate measurement of power impossible. An engine can turn much higher rpm with a prop while stationary, but this rpm always drops when the prop is properly loaded by traveling forward thru the air. This is why I believe the majority of measured HP figures printed by RCCA are inaccurate.

Unless there are ways to account for prop wash and air density's effects on propellers, I personally would never put any stock in the results from these types of tests.

I hope this answered any doubts people may have to the accuracy of my dyno's figures.

Sorry for the long post.

JPHRacer: my dyno uses software originally developed to test full size v-8 race engines. Since then the same software has been adapted to test many different size engines, from r/c glow engines, gas r/c boat engines, go-cart engines, motorcycle engines and even 1500 hp alcohol fueled dragster engines. This software has proven itself time and time again. Thanks for helping to explain the differences.


BK

So how is Novarossi claiming their HP figures? They say 1.5 - 1.6 for their latest 3p -5p .12 engines. I like how your doing this 4 stroke testing, but I just wish their was an industry standard of HP values being used out there so as consumers we arnen't biffed. There should be one source all manufacturers get their hp numbers and that should be through someone 3rd party like you. Imagine if we as consumers got the industry to use a 3rd party dyno checker to get their numbers, kind of like a ROAR approved engine list. Would you be willing to perform this service (paid of course by manufactures)?

Tomkelly,
Hopefully this is what will happen soon. I am not planning on testing for all manufacturers, at least not at this time, but, I am offering my dyno's for sale to all manufacturers, or anyone else who want's one for that matter. I hope my dyno WILL become the industry standard and we can get some consistency from all parties.

So far I have quite a few manufacturers of engines already awaiting their dyno's and even more interested and awaiting a demonstration that will take place in October. Hopefully all will follow suit and we will get some consistency.

However I am not opposed to doing testing for manufacturers from time to time.

BK

Progress report...
 

Hello all,
I just recieved a OS FS-26S-C Ver II today from OS. I am going to dyno it this weekend. I will post results when I am finished. No major differences, except carb and valve cover. Rocker arms look a little different but as far as I can tell they are the same ratio. Maybe a different material.

I also just finished a pair of Titanium valves and a lower cyl for my other test 26S-C, I will test them also and post results.

Till then,

BK

mxwrench,
So you happen to have any pictures of that new .26?
How did the carb and valve cover change?
The engine is still available but only in Japan is that right?

Let us know how much faster the new .26 is over the old .26. Not sure whether I should buy the new one to replace my current engine.

Nr1Drillah, there is a pic of it in the RCCA forums.

Thanks, but where is that?
You wouldn't happen to have a link now would you?

Thanks, Drillah

Thanks Dan.

Since this engine likes to get REALLY hot, I wonder why they did not make the new one with bigger fins or even put some fins on the valve cover.

:confused:

OS FS-26S-C VerII
 

Hey guys, here are a few photos of the new Ver II I recently aquired. I checked this new engine over very carefully and I noted the following changes:

New carb with single needle w/5mm bore and new type manifold --> up from 4.6mm previous

New valve cover --> not sure why, maybe for logo placement

New design rocker arms --> slightly larger arm and much better material. Probably to prevent flexing.

Slightly thinner piston skirt thickness --> lighter weight

A few other cosmetic changes --> new machining on crankcase, new backplate shape

Sorry, no increased lift or duration of cam shaft

Here is a photo of the new engine next to the old one...


BK

Ti Valves
 

One more thing, here is a photo of the Ti valves I made. I will test these and a ported head with more compression on Saturday and I will post the results.

Also I will do a base line test of the new Ver II in its stock configuration and I will post those results also.

Stay tuned...

BK

Dude i love what your doing keep up the good work!!!!

I just found this thread after having already posted on the one about asking ROAR to allow four strokes. So, this will be pretty much the same stuff I posted over on that thread. Anyway, I've been running the FS26SC in a Super Nitro for just over a year. It has proven to be competitive with the .12 and .15 two strokes. I have had some trouble with the two-speed in the Super, and the class looks like it's on its way out around here, so I have recently transplanted it into a Nitro TC3. I don't have a dyno, but I have learned a few things over the last year.

First, a reliable two speed is a must. Contrary to popular belief about the broad torque and horsepower band of the four stroke, they do have a narrow power band in which they work best. That, and you simply cannot afford to over-rev one. You'll pay for that in valve springs and valve adjustment screws. In the real world, this means if you gear low enough for some grunt out of the corners, it will run out of RPM faster than a two stroke. If you gear it for top end on the straights, that famous "low end torque" that you were counting on to pull it out of the corners will fail you. In most parking lot racing, at least around here, the two strokes almost never shift even if they have a two speed. They pretty much stay in first gear, and they can rev high enough to do that. Four strokes can't.

I have run a number of induction and exhaust combinations in the last year. The stock carb and the exhaust pipe/muffler combination sold as the four stroke conversion kit for the Super Ten produced the least power. It was also difficult to tune the motor so it was not rich on the bottom end and lean on the top. To cure this, I mounted a manifold from the FS40SC, which accepts an O.S. type 10 two needle carb. This change made a world of difference in tunability, and picked up some top end. The next change was to go to the larger diameter header pipe sold by O.S. and advertised as increasing power. This change pretty much killed low end, without that much of a noticable gain on the top. The next exhaust mod involved screwing a short header pipe from an FS 90 into the adapter that came with the larger header pipe. On the end of this was mounted a muffler from the same FS 90, and the exhaust was routed out the back of the car rather than down this side like a tuned pipe. The straight through flow made a big difference in power, but I felt the pipe was too large in diameter to provide adequate scavenging. The next step was to go back down to the original 1/4 inch exhaust diameter, but this time as a straight pipe. This provided the most power yet, but was way too loud to run in mall parking lots. Another sneaky advantage was none of the other drivers could hear their cars running, which made them a little harder to drive.

The next step will be to take what I've learned and apply it to the NTC3. The challenge will be to find an exhaust system that will work and gearing to take advantage of the four stroke. I can't use what I made for the Super Nitro, as it is belt drive and the NTC3 shaft drive, which will require a whole new exhaust layout. The gearing for the NTC3 is also more limited than what I could do with the Super. I'm hoping to have this thing sorted this winter and ready for next season. I also have an NTC3 with a pretty hot RB .12 that I ran this year, so it will be interesting to compare them side by side.

Anyway, sorry about the long post. I'm pretty into this four stroke thing, and I've looked for a long time for a site that has some information on them. I'm glad I finally found a site where I can compare notes with some one else that is into them.

Super Nitro Division
 

Maybe not Jeff, you may be able to keep the weedwacker going in the Super Class. I have 4 new entries for next year already. Drew and 3 of his buddies are going to field Supers so there will be enough to run them on their own. :nod: ;)

Re: Super Nitro Division
 

That's good to hear, Ben. Now that both cars are set up for the four stroke, it's a snap to swap it back and forth. I still need to sort out the two speed problems in the Super, though. A clutch type would really help. Alex wants to run nitro next year, so right now it looks like he might drive the car I ran all of this year, and I'll drive the Weedwacker II. Either way, we're field two nitro cars.