Author Topic: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine  (Read 98697 times)

Offline lohring

  • Full Member
  • ****
  • Posts: 146
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #255 on: July 25, 2017, 02:35:40 PM »
We tested a lot of different fuels over the years.  The fixed head 26 cc gasoline engines don't benefit from much but the lowest cost fuel.  You need to be able to optimize the compression, ignition timing, and especially the pipe design for each fuel.  When you can only change the mixture the graphs below show what happens.  Note that the ethanol fuels seriously lower power if you don't richen the mixture.  The variation in peak power is probably not significant, though but there is variation in the low end and over rev area.  By the way, the tested E10 was actually 30% ethanol, the E85 was 60% ethanol and the 92 octane was 8% ethanol.

Lohring Miller

Offline DRT

  • Full Member
  • ****
  • Posts: 62
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #256 on: July 25, 2017, 08:29:53 PM »
We tested a lot of different fuels over the years.  The fixed head 26 cc gasoline engines don't benefit from much but the lowest cost fuel.  You need to be able to optimize the compression, ignition timing, and especially the pipe design for each fuel.  When you can only change the mixture the graphs below show what happens.  Note that the ethanol fuels seriously lower power if you don't richen the mixture.  The variation in peak power is probably not significant, though but there is variation in the low end and over rev area.  By the way, the tested E10 was actually 30% ethanol, the E85 was 60% ethanol and the 92 octane was 8% ethanol.

Lohring Miller

Thanks Lohring,

The main reason I asked Jim the fuel question was because I wanted to know which fuels he was actually optimizing his pipes for. On the topic of alternative fuels it makes sense that you'd have to richen the ethanol fuels. I think this is what kind of defeats the novel idea that they would be the wave of future fuels in automobiles when you have to basically double the mixture as opposed to gasoline to do the same work. Essentially you'd also save no coin at the pump.  I had a flex fuel Tahoe but never tried it because everyone I talked to said their flex vehicle ran terrible with it.

BTW
Have you done any work with toluene as a fuel in a two stroke? Also have you contemplated a workable FI system for a 2 stroke in the displacements run in the RC boating organizations?
« Last Edit: July 25, 2017, 08:34:18 PM by DRT »

Offline lohring

  • Full Member
  • ****
  • Posts: 146
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #257 on: July 26, 2017, 02:42:12 PM »
You could argue that all the tuned pipe glow ignition engines are throttle body fuel injected.  Pipe pressure forces fuel into the carb.  Since pipe pressure varies with power output, this is a very crude regulating mechanism.  In the past crankcase pressure was also used.  Jim has used this same system on gasoline fueled spark ignition engines, but we mostly stuck with modified Walbro pumper carbs.  They gave problems at high rpm even with lower pop off settings and other tweaks.

We did not experiment with any gasoline additives other than the methanol and nitromethane we had on hand.  We mostly wanted to convince ourselves that fuel cheating wouldn't give big power gains.  Since these tests some other additives have been suggested, but we never tried them.  Below is the article I wrote on the testing.

Lohring Miller

Offline Admiral_dk

  • Full Member
  • ****
  • Posts: 1873
  • S°ften - Denmark
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #258 on: July 26, 2017, 09:33:58 PM »
Thank you for showing the full article - it helped understanding the graphs even better  :ThumbsUp:

Best wishes

Per

Offline strictlybusiness1

  • Full Member
  • ****
  • Posts: 266
  • ME., Tool Maker
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #259 on: August 10, 2017, 11:48:49 PM »
Mr. DRT,

I'm unable to use the articuulated ball & pin universals on this project because there would be an excessive angle where the stuffing tube exits through the bottom of the hull. Placing the engine as far forward & as low as possible made the use of a cable drive necessary. Sometimes you gain in one area only to lose in another.

JA

Offline DRT

  • Full Member
  • ****
  • Posts: 62
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #260 on: August 28, 2017, 10:34:29 PM »
Thanks for the update. With that hull and motor you probably have a legitimate shot at a gas cat record if you can hold it in the road. I'm curious will the skeg be a hindrance in all out speed endeavors? Do you plan on using the new carb setup on it with the pipe?

In the meantime I hope you're willing to share photos and how you find the engine timing numbers, without a degree wheel, that you enter in the pipe programs you use to build the pipes. I think the real engine builders here will appreciate it and actually have the know how to apply it in their own DIY engine projects versus the average off the shelf consumer.

It was never explained by OE consumers how "precise measurements are made" for the numbers that would used with the Employee Assistant Programs... sorry I meant Engine Analysis Programs. :Doh:
« Last Edit: August 29, 2017, 08:42:47 PM by DRT »

Offline lohring

  • Full Member
  • ****
  • Posts: 146
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #261 on: August 29, 2017, 01:06:15 PM »
There are a lot of available piston position calculators available.  Attached is one.

Lohring Miller

Offline strictlybusiness1

  • Full Member
  • ****
  • Posts: 266
  • ME., Tool Maker
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #262 on: October 02, 2017, 10:07:19 AM »
After successfully chroming approximately 1500, #4032 aluminum cylinders, I will show the final changes made to the #360 free machining brass, cylinder holding fixtures. Each fixture could be used twice to chrome a cylinder. There are reasons I prefer not to do this. The build up of chrome on chrome that takes place behind the cylinder ports on the brass holding fixture & the build up of chrome on chrome that takes place at the top & bottom of the brass holding fixture. Since this build up of chrome must eventually be removed  from the brass holding fixtures, any decrease in the amount of time required in the HLC bath is desirable.

I will post the photos latter.

Jim Allen 

Offline DRT

  • Full Member
  • ****
  • Posts: 62
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #263 on: November 08, 2017, 03:21:28 AM »
James,

I truly hope you and Lohring continue share the things you learned here about performance two stroke engines and how to build them. This seems to be a much better place to receive intelligent questions, and have your intelligent responses be accepted. It's increasingly tiring to have the passing of knowledge from people like Fritz Overmars, and yourselves repeatedly sidetracked by individuals that have nothing better to do than complain about it's usefulness due to their lack of understanding and/or ability to build the parts necessary!

Thanks for all you do,
Hugh

« Last Edit: November 08, 2017, 03:26:41 AM by DRT »

Offline strictlybusiness1

  • Full Member
  • ****
  • Posts: 266
  • ME., Tool Maker
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #264 on: November 10, 2017, 11:26:57 PM »
Hugh,

I have been taking some time off to get things in order. Getting ready for a possible move in the East direction to be closer to the running sites. Working on a special rudder setup for the cat. No problems with the situation you referred to. Catch you latter.

Jim

Offline strictlybusiness1

  • Full Member
  • ****
  • Posts: 266
  • ME., Tool Maker
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #265 on: November 29, 2017, 11:06:28 AM »
Lohring Miller will be looking at how his engine analysis program results compare to the actual dyno & on lake performance of the new tuned pipe chamber. He has found that previous tests of the tuned pipe used on the out rigger type hydroplane & the computer analysis are very similar performance wise. This is a big help when attempting to build tuned pipes in the future because it gives a direction to start with.

Jim Allen

Offline Admiral_dk

  • Full Member
  • ****
  • Posts: 1873
  • S°ften - Denmark
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #266 on: November 29, 2017, 11:45:18 AM »
That is very interesting news  :praise2:

I use simulation tools for a lot of my professional work - designing music equipment http://www.emmaelectronic.com/ so I really appreciate the difference between accurate models and all else  :ThumbsUp:

I expect that you still need to measure the exhaust temperature of the engine in order to get the simulation as close as possible - considering what Lohring has disclosed so far in earlier post in this thread.

Looking forward to more info on this subject  :)

Offline lohring

  • Full Member
  • ****
  • Posts: 146
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #267 on: November 29, 2017, 01:48:17 PM »
I use a program called EngMod2T.  (http://vannik.co.za/EngMod2T.htm)  As you noticed, it needs a very careful input of temperatures and other data to give accurate results.  I compare its results to the extensive dyno data we collected over the years.  It tends to be a little optimistic  because 26 cc engines have larger friction losses as a percent of power compared to say 125 cc engines.  It's really helpful in evaluating tuned pipe designs.

Lohring Miller

Offline strictlybusiness1

  • Full Member
  • ****
  • Posts: 266
  • ME., Tool Maker
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #268 on: February 04, 2018, 02:25:38 PM »
The two tuned pipes shown in the photo are similar, but they are used on different hull types. The chamber painted black is used on a rigger & the un-painted chamber is used on a cat. Both are used for oval racing. Their major diameters are the same, but the tuned length of the unpainted chamber is longer. This longer tuned length is because of the smaller included angle of the baffle cone used on the un-painted chamber. Also the unpainted chamber has no straight flex section & a much shorter flanged header section. Both chambers have a total internal volume that is approximately 24 times the displacement of the engine. A very important fact that allows the use of a long, small ID stinger for the maximum boost amount possible!

Jim Allen

Offline lohring

  • Full Member
  • ****
  • Posts: 146
Re: .90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine
« Reply #269 on: February 04, 2018, 03:42:52 PM »
I just recently came across a very interesting tuned pipe calculation spreadsheet.  It's for the highest performance engines with a bridged or triple exhaust.  It calculates both the pipe and the exhaust passage from the piston into the pipe.  This is all empirical, but is based on some very experienced two stroke engine builders experience. 

Lohring Miller