Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 98548 times)

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #240 on: June 01, 2017, 05:31:34 AM »
If you get the chance I would like to see the Toroidal head you cut for the .90 engine. Did you mill it or create a turning tool for the lathe? Will the Toroidal head change what would be the optimal tuned pipe for the motor?

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #241 on: June 01, 2017, 09:00:08 PM »
I do not see any change to the optimal pipe design. Maybe this is happening because the engine's operating temperature for both the gas & nitro engines did not increase a siginificant amount. Remember that the star characteristic of the Toroidal design is the elimination of any detonation at very high compression ratios. The interesting thing is that the Toroidal design seems to work the same in both types of engines. I searched for the print of the toroidal head used on the .90 cuin nitro engine. It is similar to the chamber used on the gas engine because the ID's are close to the same. 1.339" for the gas & 1.125" for the nitro. I used the same size ball nose mill but at a different location from center. Milling of the chamber is done on a rotary table. Be carefull with the milling as small changes with chamber size & depth can make a difference.

JA
« Last Edit: June 01, 2017, 09:30:00 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 #242 on: June 01, 2017, 09:54:10 PM »
Jim are your drawings supposed to be rotated around the "centre of the plug" so to speak ?

If so, what is the "curved" line under the plug with any dimensions in the top drawing - the top of the piston or a reference line ?
If not - not much squish band or ...?

On the bottom drawing you seem to have three different curves for the "roof" - does that mean that you got a "multi-shaped roof" ?

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #243 on: June 01, 2017, 11:16:57 PM »
Maybe I'm wrong but I think the line is the top of a domed piston. This leads me to ask which style piston gave you the most increase in performance when used with the Toroidal head? I guess in the nitro motors a flat top is the only thing available from manufacturers of boat motors so you'd almost have to get into machining your own pistons if you wanted any thing else.

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #244 on: June 02, 2017, 12:33:15 AM »
The curved line in the top drawing is the piston crown of the gas engine. The straight line in the bottom photo is the piston crown of the nitro engine. Notice that the ground straps & the tip of the center electrode is .015" away from the piston crown at TDC. Most engine builders cannot believe this does not cause a hot spot on the piston's crown. Also there is no death ash visible on the underside of the piston. The radius on the piston crown helps to cool the piston crown because the incomming charge will attach to it. Also look at how close the glow plug will be to the piston at TDC in the .90 cuin nitro engine. The dimension is what would be found in .45 cuin engine.

I have not looked at the difference in performance between a flat top piston & a curved piston. The two engines operate at very different RPM ranges, different deck clearances, different squish velocities, different fuels, etc., etc. The flat top pistons used in the nitro engines & the domed pistons used in the gas engine are both custom machined.

Jim Allen

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #245 on: June 02, 2017, 01:03:05 AM »
When you compare this drawing of some of the original Toroidal heads tested in gas engines, it will be obivious that there has been a substantial increase in the engines compression ratio without detonation problems. Concentrate on the figures indicated in red. These niumbers are where the next to last head design was tested. Notice the depth of the chamber & its location from center written in red. The photo shows the actual piston crown & head after many hours of running.

JA

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #246 on: June 19, 2017, 11:11:19 PM »
The original tuned pipe's center section of 2.750" in length, was reduced in steps down to 1.000". This is easily done by un-silver soldering sections that are machined to fit inside each other & re-maching the undercut areas with the fixture shown previously. This change allowed the engine RPM's to reach 20,600+. We also increased the oil content from 12 ozs/gal to 14 oz/gal. By shortening the center section's length instead of shortening the head pipe's length, the bottom end & mid range torque were unaffected. However, the tuned pipes total volume & tuned length have been decreased. Also with increasing the engine's RPM & power, there is a narrowing of the engine's maximum power band. There was also an increase made to the engine's cooling system.

JA
« Last Edit: June 19, 2017, 11:16:29 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 #247 on: June 20, 2017, 11:43:02 AM »
Very interesting Jim - I wouldn't have thought of "just" shortening the centre part as the best way to go  :ThumbsUp:

I just realized that I somehow missed that you're using a lot of bolts to hold the head in place - I can't remember ever seeing anything but four bolts for the cylinder + head on all racing two-strokes over 50cc - but you use TEN  :o
I'm guessing that you do this to prevent distortion of the head ....

Again thank you very much for sharing your expertise with the rest of us  :praise2:

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #248 on: June 20, 2017, 02:32:41 PM »
I built a pipe with a variable center section as well as a variable length header.  That allowed testing the variation in diffuser and baffle cone position separately.  It turns out that the diffuser position isn't very sensitive and that the tuned length is determined by the baffle cone position.  Below is a dyno graph with a fixed header length and different center section widths compared to an M&D pipe.

The pipe was designed with a high horn coefficient diffuser to deliver a large "suction" pulse that overcame the intake restrictions in earlier Zenoahs.  It added nearly 20% more power.  Later intake and transfer modifications reduced this restriction and the pipe worked the same as a standard pipe.  It is still a good pipe for stock Zenoahs.

Lohring Miller

Offline Admiral_dk

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #249 on: June 20, 2017, 09:45:10 PM »
Thank you very much for the curves Lohring - rather informative   :praise2:

The end before the "stinger" - is that a "strong point" for the support of the adjustable length or a cone going down to the smallest diameter and a bigger diameter tube leaving as suggested earlier and if so, why is it followed by the smaller diameter tube ?

Offline lohring

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #250 on: June 21, 2017, 01:33:45 PM »
The fat end of the baffle cone is threaded for a screw in stinger.  We tried several different stinger diameters as well as an inverted stinger.  An inverted stinger goes back into the pipe to the center section, quieting the pipe.  Our testing showed the same power as the standard position.

Note the difference in the diffuser section on this pipe compared to Jim's.  This pipe has a high horn coefficient.  Pipes designed for peak power have a lower horn coefficient, that is the diffuser doesn't flair as much.

Lohring Miller

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #251 on: July 13, 2017, 11:08:33 PM »
Hi Jim,
I saw on another site someone suggest to you ultrasonic cleaning to prepare your pistons for fitting. I would advise against this for pistons made from aluminum. I use Ikohe E60H and E 300 H Elmasonic ultrasonic cleaners at work to clean the paint bell cups that spin at 60K on the Sames electrostatic paint applicator bells fitted to the 7 axis fanuc machines I service at Daimler. At 37Khz these machines can peak nearly 2 hp of energy and erode certain materials due to cavitation. This cavitation was enough to pit an aluminum bell cup we tested. The titanium ones one the other hand held up. This is enough to lead me to believe that the results on an aluminum piston and other types of metals and materials would be less than satisfactory! This may explain why their cleaning tanks are made from cavitation resistant stainless steel and why Bob has no problem cleaning dental tools with them.

Take Care....
 
« Last Edit: July 13, 2017, 11:18:07 PM by DRT »

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #252 on: July 16, 2017, 12:44:35 PM »
Very good information my "Puppy",

Even engines that have been buried in the ground at a 200 MPH speed are washed in a 50% solution of Ultra Dawn & Super Strength Greased Lightening. A hot water rinse brings all the aluminum & steel parts back to like new condition.

JA
« Last Edit: July 16, 2017, 04:55:13 PM by strictlybusiness1 »

Offline DRT

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #253 on: July 24, 2017, 10:12:01 PM »
 :Lol:
Hi James,
Just curious on your tuned pipes what octane gas and percentage nitro methane are your gas and nitro pipes optimized for respectively?

Offline strictlybusiness1

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Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #254 on: July 25, 2017, 03:41:10 AM »
I use ethanol free, regular gas from the pump in my gas engines. There are some gains to be found with oxgenated fuels, but this would be illegal. I use HP-2 in my gas engines with 10 to 14 ounces/ gallon. My nitro engine uses 80 % nitro methane, 12 % ethylene oxide & 8 % oil. The oil is 2/3 Klotz & 1/3 Blendzall racing cartor.

JA