Engine observation and question

I'm an old engine builder ( 72 in March - started around 1961 LOL ) and although I have modified nitros in the past, my focus is in gas power. But over the years, I have seen many models of nitro engines come to market. The thing that strikes me is, almost all of them are still using the standard vertical port platform in the cyld. castings. Most of these engines are quite small, and I can't see where physical "space" would be an issue. Purpose built gas motors have used the more modern/efficient tea cup arranged ports for some years now, and more are coming. Lohring Miller is very familiar with gas and nitro development and he, among others, knows plenty about flow. I would like to hear of any insight others may have.

For the cost of the nitro engines, and the number of decades they have been basically the same, I'm just wondering why there isn't more development forthcoming?

Take a look at the new Novarossi and CMB cylinders that are using a 3 port exhaust port . As far as the large radius transfer passageways there is some straight area in the cases yes . I imagine size and volume are considerations . As far as being basically the same ...yes they still burn Nitro !!

Dennis Somers said:

I'm an old engine builder ( 72 in March - started around 1961 LOL ) and although I have modified nitros in the past, my focus is in gas power. But over the years, I have seen many models of nitro engines come to market. The thing that strikes me is, almost all of them are still using the standard vertical port platform in the cyld. castings. Most of these engines are quite small, and I can't see where physical "space" would be an issue. Purpose built gas motors have used the more modern/efficient tea cup arranged ports for some years now, and more are coming. Lohring Miller is very familiar with gas and nitro development and he, among others, knows plenty about flow. I would like to hear of any insight others may have.

For the cost of the nitro engines, and the number of decades they have been basically the same, I'm just wondering why there isn't more development forthcoming?

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Call Cmb and speak to the designer.  Then call Novarossi and speak to the woman that owns it.  You will know your answer . 

Jeff. Could you in lighten us & save the trouble ?

Sent from my SM-N920V using Tapatalk

Jeff; I am with Alan, I would like to be in lighten too.        J.

You can learn a great deal about miniature two cycle engines, including their tuned pipes, transfer shapes, carburetors, metallurgy, fitting tolerances, etc. only by building them from scratch! Knowing exactly what the "number being used is" & being able to make that number teaches you what direction to go in over time. Attempting to modify another engine builders mistakes will teach you very little!

Jim Allen

As far as the basic shape of any transfer used in a high performance miniature two cycle engine or a large size two cycle engine, it has been conclusively proven, that the standard "tea cup shaped transfer" developed by Professor Gordon Blair, may not be the best! The radiused shaped transfers used in the MB-40 allow it to easily run at 32,000+ RPM & the engine is still breathing. This type of transfer is also used in Aprilia 125 CC racing motorcycle engines & late model QD engines. Notice the width of the exhaust window in the photographs. It doesn't matter how efficient the transfers are if the window geometry used doesn't allow the engine to breathe!

JA

 I'm very familiar with Jan and Frits work at Aprilia and that's the kind of modern porting I'm addressing. And while that basic configuration has been used for motorcycles, personal water craft, Rotax, Yamaha and Honda, MB40 pylon air craft and others, my enquiry has to do with commercially available marine nitro engines. This is why we are on International Waters. And while scratch built is expensive, creative and interesting, it doesn't help the common modeler who is looking for a better product off the shelf that they want to buy now.

To be clear;

58 years of building, modifying, and racing ( full scale and models ) land and water vehicles doesn't help a regular guy's bank account LOL. But it can sure teach you to recognize improvement possibilities in commonly available products and turn them into winners. For those that don't know what my son Peter and I ( SRI Motorsports ) are about, we currently modify SRI Pioneer marine gas engines. These engines are an excellent platform to build on, and share some design features of the Aprilia work. Our personal focus is on SAW trials, but most of the units we have done, are for heat racing. We like to talk about and show some of our work, but we also prove our work. Our Pioneer motors have only been entered in two official ( IMPBA ) sanctioned events so far, and both times they helped to produce world records. One of our customers runs over 100 MPH ( unofficial ) with an under 27cc gas cat, and has that class record.

But this thread is not about what individuals do, so let's try to get back to commercial nitro marine offerings.

Thanks for joining the conversation!

Some great pictures Jim!! Stock power improvements are always appreciated by us none motor experts. The manufactures of motors for us boaters and the hobby itself (cars , airplanes and boats) has dwindled over the years with the better electrics on the market. Seems that the plug and play aspect is the way new people want to go, and the nitro and gas tuners are a dieing breed.

Thanks for the great work you guys do and keep educating us old guys

Brad

Dennis Somers said:

 I'm very familiar with Jan and Frits work at Aprilia and that's the kind of modern porting I'm addressing. And while that basic configuration has been used for motorcycles, personal water craft, Rotax, Yamaha and Honda, MB40 pylon air craft and others, my enquiry has to do with commercially available marine nitro engines. This is why we are on International Waters. And while scratch built is expensive, creative and interesting, it doesn't help the common modeler who is looking for a better product off the shelf that they want to buy now.

To be clear;

58 years of building, modifying, and racing ( full scale and models ) land and water vehicles doesn't help a regular guy's bank account LOL. But it can sure teach you to recognize improvement possibilities in commonly available products and turn them into winners. For those that don't know what my son Peter and I ( SRI Motorsports ) are about, we currently modify SRI Pioneer marine gas engines. These engines are an excellent platform to build on, and share some design features of the Aprilia work. Our personal focus is on SAW trials, but most of the units we have done, are for heat racing. We like to talk about and show some of our work, but we also prove our work. Our Pioneer motors have only been entered in two official ( IMPBA ) sanctioned events so far, and both times they helped to produce world records. One of our customers runs over 100 MPH ( unofficial ) with an under 27cc gas cat, and has that class record.

But this thread is not about what individuals do, so let's try to get back to commercial nitro marine offerings.

Thanks for joining the conversation!

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Nice plug Dennis.

Jim these engines are irrelevant to boating unless you you throw a water jacket on top...But how can these engines compare to Current marine engines anyway ..Nova 21 engines allready exceeding 40-43000 rpm.in stock condition

David, thanks for the comment. But we have no interest in drumming up more business than we have. Keeping model boating at a "hobby" level, is where our fun is.

Almost all the American innovators in model engine design are long gone.  Quickdraw are the only people I can think of these days.  The only new developments in larger modern two strokes involve fuel injection, mostly to control emissions.  Except for model cars, power in models has gone to low cost, industrial style, gasoline engines and electric motors.  Unless you have a source for low cost manufacturing, I wouldn't expect anything new at the model level.  Jim has pretty much covered where the state of the art has been for years. 

Lohring Miller

If you believe CMB's claim of 3 hp for their latest 3.5 cc Beta 21 then we're not far off the power/cubic inch top fuel dragsters make.  That running somewhat less than 90% nitro and w/o a supercharger.

A fuel car is estimated to make 10,000 hp for a 500 ci engine = 20 hp / ci.  

The CMB Beta Evo 21 at 3.5 hp /  0.21 ci  = 16.6 hp / ci

I find getting the available power to the track is the most challenging these days... :unsure:

With the sad passing of 2 stroke GP racing motorcycles, the multi million dollar r&d that has lead to the majority of power gains in two stroke engines is long gone.  Sure you still have snowmobiles, but they are a much smaller market and are also moving towards four strokes.  Kart racing is a small market with limited r&d.  

The real question is whether or not transfer design is holding back the power engines can produce, or are the materials we use to build the engines limiting running them at higher power outputs and/or rpm.

As you guys point out, the "state of the art" Aprilia style cyld. is many years old now, and yet even the Europeon nitro marine eng. manufacturers never seemed to bother with it. And yes, all the larger motorsports manufacturers are going 4 stroke for emissions and noise regulations at much higher manufacturing costs.

Terry that's an interesting comparison, although it's generally a given that 2 strokes make around twice the power of the same size 4 stroke. So to make that comparison, that 21 would need to be closer to 40 HP per cu. in. On a personal note; I have zero confidence in RC eng. HP numbers, because most often they are used to sell product. I prefer to see how much prop a given engine can push water.

Paul certainly better internals produced at a marketable cost is a real challenge. I think the question of newer transfer design has been answered on nitro 2 strokes ( albeit aircraft ), up to QD Pioneers in gas model marine. I'm well aware of the differences of compression, combustion, heat, ect. between nitro and gas. But in any IC eng., flow is flow. And the higher the eng. speed, the more important fast, smooth, and controlled flow into the chamber becomes. There's just a lot less time for everything to get done.

Speculation: Perhaps if the nitro marine manufacturers had gone with a newer style cyld., they may have been able to hold the line on RPM, and maybe produce more thrust. Who knows.

But it seems from what has been said, that it is what it is, and will be.

It's an interesting discussion, but we can't ignore economy of scale and the tolerances that need to be held and can be held with our smaller displacement engines.  It would seem that doing away with chromed brass sleeves and having nickosil plated aluminum cylinders with more ideal port designs would be a big performance benefit.  But the question is what works well in a 54mm bore at 14,000 rpm might not be what works best in a 21mm bore at 30,000 rpm or a 16mm bore at 40,000 rpm.  Giving up the ability to get a perfect piston/cylinder fit for a ringless piston might more than offset the gain from slightly better ports.  Slightly adding to port length and hence the volume of the crankcase and hence the ability to pump might hurt more than sticking with ports that hug the cylinder liner.  

How well an engine flows in steady state on a flow bench doesn't necessarily best model how an engine flows when that flow is starting and stopping 30 or 40 thousand times a second.

What we really need is a very passionate modeler with the drive and means to do the research to make performance strides with the ability to profit off that research as an afterthought.  Manufacturing companies have a bottom line and I don't see them dedicating 10's of thousands of dollars and years of research and refinement to increase power by maybe 5%.  

Either that or those who work in industries using new materials that would allow engines to increase rpm by 10,000 bringing those exotic materials to bear.  Then again if that results in engine prices doubling that could end up killing our sport.  If only say 5-10% of the modelers are willing to drop say $1500 on an engine and those engines are dominant, than suddenly you have one guy in the club that can afford to lap the field and the rest of the guys suddenly losing interest.

PaulHail said:

With the sad passing of 2 stroke GP racing motorcycles, the multi million dollar r&d that has lead to the majority of power gains in two stroke engines is long gone.  Sure you still have snowmobiles, but they are a much smaller market and are also moving towards four strokes.  Kart racing is a small market with limited r&d.  

The real question is whether or not transfer design is holding back the power engines can produce, or are the materials we use to build the engines limiting running them at higher power outputs and/or rpm.

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Paul,

Very thoughtful & truthful post. Even if better porting increases the HP & RPM, the limiting factor will always be the mechanical soundness of whatever engine is being used. Look at what happened when many gas model boaters began to consistently run at RPM's beyond 20,000. Engine manufacturers did not provide a rod or retainer with a better design or better metallurgy. The solution was to slot the connecting rods upper end & bottom end or use an excessive amount of lubrication. No research was done to determine if their was or is a viable solution. Lohring Miller has great knowledge about this problem. I believe this same problem will appear again as engines begin to turn at even higher RPM & greater HP amounts.

Jim Allen

FE motors rule the rpm now..

Video killed the Radio star...

David Ashcroft said:

FE motors rule the rpm now..

Video killed the Radio star...

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And why is that?  In a word, inertia.

A FE motor only does one thing, it spins due to magnetic fields in one direction with the possibility of achieving more and more speed until the load on the output prevents this.

An IC engine, on the other hand, is consistently having to start and stop a piston at each end of the cylinder.  If there wasn't a flywheel on the crank to provide the required inertia to keep the crank spinning, our engines wouldn't run.  Stopping the piston's travel at the bottom of the stroke takes away some of the power developed by the burning fuel at the top end of the stroke, which, when you really look at it, stops the piston from rising and forces it back down, lowering the power to the crank by that much more.  I know, most think the crank stops and reverses the piston, and correctly so as it limits how far the piston can travel, at the bottom of the stroke.  At the top end, however, the burning fuel has as much to do with reversing the piston's direction as the crank since the fuel starts burning while the piston is still rising, which actually slows the piston until it gets past TDC, when the pressure from the burning fuel is able to push it down again