Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 88295 times)

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #45 on: July 21, 2014, 12:51:03 PM »
Jim I was wondering what type of balancing you use with your engines, static or dynamic. I am sure at 30000+ rpm balance is a major factor and some what of a black art.

In the beginning I attempted to use Ricardo's formula for balancing single cylinder two strokes. This work well for lower RPM engines (15,000 to 20,000) & engines that use a  hanger type piston. It doesn't work with piston boss type pistons & engine RPM's of 30,000+. I found that 33% of the total reciprocating weight plus the total rotating on the crank counterbalance allows the engine to run smoothly in the 20,000 to 30,000+ RPM range. The full disk crankshaft I used required the addition of two 5/16" OD Mallory metal slugs to get the balance where the engine ran the smoothest at WOT. Another cut & try experience.

JA

Offline steamer

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #46 on: July 21, 2014, 01:28:16 PM »
Welcome to the Forum Jim!   That's some mighty impressive work you have there!   

Following along....

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #47 on: July 22, 2014, 03:28:40 AM »
If anyone is interested, I would take the time to explain in detail, with photos, about the automatic fuel metering carburetors used on these engines. The carburetors are 100% maintenance free & have been thoroughly tested & used for more than 23 years.

Jim Allen

Offline v22

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #48 on: July 22, 2014, 04:21:20 AM »
Jim thanks for your contribution. This thread is absolutely amazing. I really like the photo of the connecting rods. Sure tells a story.

Is there any chance that you could start a thread on your dyno? I know there are a lot of people building their own IC engines that would love to know the power output. Information is a bit thin on the ground in this space.

Offline PStechPaul

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #49 on: July 22, 2014, 04:59:17 AM »
I am fascinated by the level of precision and effort put into these engines. It is far from anything I could hope to achieve, or even come close to, without perhaps a true passion for such pursuit of excellence. But on a more practical level, I might be interested in learning how to improve existing small two-cycle engines as found in chain saws and weed whackers. Maybe just some ideas on how to make a more reliable carburetor (which seems to be what usually goes bad) would be helpful.

It seems you have an immense amount of knowledge, and it is rather overwhelming to follow everything you have introduced in this thread. Perhaps breaking it down to some simpler concepts and components, such as the carburetor and the dynamometer, as has been suggested, in separate threads, would be easier to grasp and use (or at least attempt).

As for the dyno, I think a fairly simple and accurate instrument could be constructed using a set of reduction or speed increasing belts and pulleys, connected to a generator (such as a 2 HP treadmill motor) and a variable resistance load. The RPM can be read by a simple tachometer and the power can be determined by the actual DC current and voltage along with the previously measured (or estimated) efficiency of the generator.

I'll enjoy following along as best I can, but it would be more fascinating to see some videos, if you could post them.

Frankly I am much more interested in electric motors, controllers, and energy storage devices (mostly batteries), as I believe these will be the prime movers of choice (and economic necessity) in the near future. But there will probably always be some applications that cannot be achieved in any other way than some form of heat engine using internal or external combustion. And along with that, it would be interesting to know the efficiency of high performance engines such as those you design.

Thanks for your valuable contributions.

Offline ozzie46

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #50 on: July 22, 2014, 12:57:15 PM »
If anyone is interested, I would take the time to explain in detail, with photos, about the automatic fuel metering carburetors used on these engines. The carburetors are 100% maintenance free & have been thoroughly tested & used for more than 23 years.

Jim Allen

By all means lets hear more on the carbs. Carbs come up often. And welcome to the forum.
 Fantastic work there.

 Ron

Offline rockknocker

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #51 on: July 22, 2014, 03:30:05 PM »
Thanks for sharing the details on your dyno setup! I look forward to your next post!

Offline dieselpilot

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #52 on: July 22, 2014, 03:49:32 PM »
As for the dyno, I think a fairly simple and accurate instrument could be constructed using a set of reduction or speed increasing belts and pulleys, connected to a generator (such as a 2 HP treadmill motor) and a variable resistance load. The RPM can be read by a simple tachometer and the power can be determined by the actual DC current and voltage along with the previously measured (or estimated) efficiency of the generator.

This all depends on how accurate you want to be. The generator load is the normal way to do it, but dealing with losses in the reduction and the generator itself is too much trouble. It's much easier to measure torque directly.

Greg

Offline ttrikalin

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #53 on: July 22, 2014, 04:00:53 PM »
If anyone is interested, I would take the time to explain in detail, with photos, about the automatic fuel metering carburetors used on these engines. The carburetors are 100% maintenance free & have been thoroughly tested & used for more than 23 years.

Jim Allen

Jim
more information for the info hungry newbies like me would be much appreciated!
take care,

tom in MA

Offline tvoght

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #54 on: July 22, 2014, 04:10:41 PM »
It's my understanding that even the dynos that use generators will have the generator mounted in gimbals with an arm connected to the generator casing for direct measurement of torque. The generator is just a braking device and the measured output power is of no concern as far as engine data collection  is concerned.

Manufacturers testing a lot of large engines will sell some of the testing power into the grid to mitigate fuel expenses.

--Tim

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #55 on: July 22, 2014, 05:44:22 PM »
If anyone is interested, I would take the time to explain in detail, with photos, about the automatic fuel metering carburetors used on these engines. The carburetors are 100% maintenance free & have been thoroughly tested & used for more than 23 years.

Jim Allen

Jim
more information for the info hungry newbies like me would be much appreciated!

I agree  :ThumbsUp:  :ThumbsUp: Carburation is one of my current problems  ::)
Best regards

Roger

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #56 on: July 23, 2014, 03:34:52 AM »
Right now I'm loaded up with work again, nothing new. Please be patient.

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #57 on: August 10, 2014, 02:21:29 PM »
The carburetors I build & use do not have any type of venturi & therefore no vacuum signal to deliver the necessary amount of fuel. There are no diaphragms to be replaced, filters to clean, fulcrum arms, pop-off springs to adjust or butterfly plates. Fuel metering is done automatically after setting the single high speed needle. Since there is no vacuum signal, due to the straight through, large ID, carburetor bore, the fuel system must be pressurized. More than adequate pressure comes from the engines tuned pipe in the amount of 120 inches of water (4.36 psi) at WOT. The amount of pressure varies directly with the engines RPM's.

The automatic fuel metering is accomplished with two internal parts, one which is stationary & has a "V" shaped slot. It is located on the left hand side of the first photo along with the needle valve. The second part, which is a tube, fits over the "V" shaped slot. As the barrel is rotated, the "round hole" in the tube closes of the "V" shaped slot & meters the fuel automatically. The rotating barrel's end points, full open & full closed positions, are controlled with a pin mounted in the side of the barrel. The pin engages the plate seen in the bottom right hand of the first photo.

All the internal parts of the carburetor are made of 303 stainless steel. The needle valves have precision ground tapers & are made of 52100 full hard steel gauge pins. The photos show the fixture used to bore the carburetor's bore (.625") & drill the hole for a .0625" dowel pin which holds the rotating tube in place. The rotating metering hole engages the "V" slot exactly & this same piece has a threaded end to mount the throttle arm. Also shown is the fixture used to make & bend the needle valve's retaining spring. The retainers are made of #172 beryllium copper which is fully hardened. The last fixture is used to cut the "V" slot in the stationary piece. The "V" shaped slot is cut very deep in this piece & it could not be done without the fixture.

These carburetors have proved themselves to be 100% maintenance free & highly wear resistant. They can be used with gasoline as well as nitro methane based fuels.

Jim Allen

Offline gbritnell

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #58 on: August 10, 2014, 05:00:35 PM »
Jim,
I've been following your thread and your work is first rate. I appreciate your photos and explanations. Having built miniature I.C. engines for a good number of years I have played with many types of carbs. I do have a very sophisticated O.S. carb that has a similar setup of which you describe. It has a small tapered slot around which the barrel rotates to control fuel flow through the idle and mid range. It also has needles to help assist in low, medium and high fine tuning.
For my type of work the biggest problem I see is trying to calculate the required slot taper and the amount that the barrel has to rotate to uncover a given area of fuel flow.
It's a very simple setup for your purposes using the 2 stroke pulses to pressurize the fuel system which is common to RC engines but I'm afraid trying to adapt this to my small 4 cycle engines would actually involve more complexity than what I currently use.
It does give me more insight into other systems being used, thanks.
gbritnell
Talent unshared is talent wasted.

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #59 on: August 10, 2014, 06:21:34 PM »
Jim,
I've been following your thread and your work is first rate. I appreciate your photos and explanations. Having built miniature I.C. engines for a good number of years I have played with many types of carbs. I do have a very sophisticated O.S. carb that has a similar setup of which you describe. It has a small tapered slot around which the barrel rotates to control fuel flow through the idle and mid range. It also has needles to help assist in low, medium and high fine tuning.
For my type of work the biggest problem I see is trying to calculate the required slot taper and the amount that the barrel has to rotate to uncover a given area of fuel flow.
It's a very simple setup for your purposes using the 2 stroke pulses to pressurize the fuel system which is common to RC engines but I'm afraid trying to adapt this to my small 4 cycle engines would actually involve more complexity than what I currently use.
It does give me more insight into other systems being used, thanks.
gbritnell

You are totally correct about what method, system or device can be used to effectively meter the fuel from low throttle to WOT. The "V" shaped slot (60 * included angle) with its matting hole increase & decrease the fuel at an exponential rate. This feature allows the engine to throttle up & down without any hesitation, lagging or stumbling. I purposely have not talked about what can happen when the fuel system is exposed to high "G" forces as the boat is turned at speed & when there is no consideration of the placement of the fuel tank in relation to the carburetor.

JA