Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 76869 times)

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #300 on: June 25, 2018, 06:44:54 PM »
Per,

I have a much smaller volume toroidal head button which uses a semi-surface discharge type spark plug. The idea for making the plug originated from Lohring Miller. Since the toroidal head shape will not go into detonation as other head types will do when overcompressed; the question to be asked is when is the engine overcompressed? Knowledgeable two stroke engine builders & tuners taught me to look for the engine RPM's sagging in the over-rev range beyond peak HP. With the testing done thus far it would appear that this information is valid. The photos show that head with its semi-surface discharge type spark plug which has the same heat range as the standard type spark plug. One problem with this type spark plug, which has the electrodes coming from the side, rather than underneath the center electrode, is the area where spark ionization takes place will be exposed to the incoming charge. I eliminated this problem with the use of a very powerful secondary coil.

Jim Allen
« Last Edit: July 08, 2018, 07:23:04 PM by strictlybusiness1 »

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #301 on: June 25, 2018, 07:22:00 PM »
Jim

Quote
One problem with this type spark plug, which has the electrodes coming from the side, rather than underneath the center electrode, the area where spark ionization takes place will be exposed to the incoming charge. I eliminated this problem with the use of a very powerful secondary coil.

I would have thought that the extreme combustion pressure was the reason for the higher voltage requirement (Law of Physics), but I can also imagine that extreme turbulence (otherwise very desirable) could more or less prevent building the ionizing layer between the electrodes, until an extreme voltage is reached ....  :noidea:

I'm curious as to how high a compression ration did you reach here ?

Per

Offline Roger B

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #302 on: June 25, 2018, 07:34:52 PM »
I'm still following along although this is beyond my experience  ::)  :ThumbsUp:  :wine1:
Best regards

Roger

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #303 on: June 26, 2018, 07:52:36 PM »
Per & Roger,

I never bothered to calculate the exact compression ratio. However, the toroidal heads that I use have less than 1/2 the volume of a standard hemi head for this size engine. I do run compression checks as the engine ages. Typical readings of 150 psi tell me the engines single piston ring is good.

Jim
« Last Edit: June 27, 2018, 07:28:00 PM by strictlybusiness1 »

Offline AlexS

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #304 on: July 06, 2018, 07:10:56 PM »
150 psi looks like a lot for a two stroke! May I ask what kind of compression ratio are you running?

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #305 on: July 07, 2018, 03:26:18 PM »
Thanks for the plug credit.  Ideas are cheap and easy, but the actual execution deserves all the credit

Lohring Miller

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #306 on: July 08, 2018, 07:21:16 PM »
"One problem with this type spark plug, which has the electrodes coming from the side, rather than underneath the center electrode, is the area where spark ionization takes place will be exposed to the incoming charge. I eliminated this problem with the use of a very powerful secondary coil."

The photos show the original placement of the 8 0z+ black secondary coil mounted between the front engine mount arms. This mounting position completely threw off the CG of the hull, which necessitated the mounting  position shown in the latter photos.

Jim Allen

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #307 on: July 08, 2018, 09:03:04 PM »
150 PSI  :o  :o very impressive Jim  :praise2:

OK that goes a very long way towards explaining the high tension voltage requirement and then add the gas swirl inside the combustion chamber, we get there :zap:

Per

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #308 on: August 05, 2018, 10:14:07 AM »
Per,

I haven't had the necessary time to update the latest information concerning the tuned pipes. I will do this when time permits. The tuned pipes are becoming more like the stuff used by high performance two stroke engine builders!

JA

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #309 on: August 05, 2018, 09:48:00 PM »
No worries Jim.

But I will admit to being curious about the "end" off one of the stingers - never seen anything like it before.

Per

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #310 on: August 15, 2018, 08:41:25 PM »
150 psi looks like a lot for a two stroke! May I ask what kind of compression ratio are you running?

Alex,

When using the Static Compression Ratio Calculator, the static calculated compression ratio is 14 to 1. This calculated number may even be higher at the time of this writing because there have been further reductions to the toroidal head's volume. Since the engine shows no signs of going into detonation at WOT, which is the main characteristic of a toroidal head shape, further reductions in the heads volume may be possible. Also, there is no sign of the engine sagging off in the over-rev range, which would indicate the engine is overcompressed. I'm not sure what influence the latest tuned pipe design has on whats taking place.

Jim allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #311 on: August 15, 2018, 08:47:50 PM »
No worries Jim.

But I will admit to being curious about the "end" off one of the stingers - never seen anything like it before.

Per

It's a simple design, low restriction type muffler. The stingers ID & length will determine how much restriction can be used without raising the engines operating temperature at WOT. Haven't looked at the DB reduction for this type muffler, as yet.

JA

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #312 on: August 15, 2018, 09:12:54 PM »
It's interesting to see the performance differences that are possible when small changes are made to similar type tuned pipes, which are being used on the same 26 & 27 cc engines. The three pipes shown have different power curves, different peak HP amounts, different peak HP band widths & different over-rev characteristics. I believe all shown could be applied to oval type racing.

Jim Allen
« Last Edit: August 15, 2018, 09:32:40 PM by strictlybusiness1 »

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #313 on: August 16, 2018, 11:44:41 AM »
Quote
It's a simple design, low restriction type muffler.

Ah - I didn't realize this - thank you for the explanation. I have only used absorption mufflers and only seen that type on two-stroke racing bikes too.

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #314 on: October 25, 2018, 10:02:57 AM »
Hey James I have to switch gear for a moment but we need to talk. Email of call me Asap!

Detonation has a very useful application thats extremely powerful. I'm sure you will appreciate this!
Say hello to the pulse detonation engine.
https://psp-tsp.com/index.php?id=203
« Last Edit: October 25, 2018, 10:10:04 AM by DRT »