What nitro percentage in a 2 stroke?  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> RC Fuels >> What nitro percentage in a 2 stroke?
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[Poll]

What nitro percentage in a 2 stroke?
0% nitro
  5% (4)
5% nitro
  8% (6)
10% nitro
  34% (23)
15% nitro
  25% (17)
20% nitro
  14% (10)
30% nitro
  4% (3)
More
  5% (4)


Total Votes : 67
(last vote on : 3/21/2008 7:59:47 AM)
(Poll will run till: -- )
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What nitro percentage in a 2 stroke? - 10/31/2006 6:54:26 PM   
fadi81



Posts: 268
Joined: 9/11/2006
From: Luxembourg, LUXEMBOURG
Status: offline 		Hi All
Just curious, what percentage of nitro do you usually use on a 2-stroke engine. And why does it differ for a 4-stroke engine?
I've started with 10% nitro, then wanted to try the 5% and I've found myself not idling as smooth as with the 10%.

I think I will just finish this gallon of 5% nitro and revert back to the 10%.
How and why does this percentage affect the engine's operation?

Though cheaper at 5%, I think I prefer to have the more reliable idle with the 10%... I will not bother to try 15 %

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RE: What nitro percentage in a 2 stroke? - 10/31/2006 8:28:17 PM   
carrellh



Posts: 3529
Joined: 3/30/2003
From: Garland, TX, USA
Status: offline 		I do not know the exact reasons "why" but my Thunder Tiger, Magnum, and ASP engines (two stroke and four stroke) run better on 15% than 10%.

RPM on a given prop is several hundred higher which is easily attributable to the nitro. It adds oxygen so you run a richer needle setting. That puts more fuel into the engine. More fuel, along with the added oxygen, makes more power. Fuel economy suffers but I haven't measured how much.

Idle and transition is also better. I have no idea why.

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RE: What nitro percentage in a 2 stroke? - 11/1/2006 2:31:08 AM   
downunder



Posts: 3193
Joined: 10/10/2002
From: Adelaide, AUSTRALIA
Status: offline 		I use zero nitro in everything because flying for sport means I'm not after all out power. A slightly larger engine or a lighter model will equal (or better) using nitro. As for an idle, if the model won't move and slows down in flight to the point it stalls then the idle is as low as is needed.

The main reason idle can get better with more nitro is because of the engine's compression. Most engines are designed with fairly low compressions to suit the American market and their love for nitro. This low compression works against low or zero nitro because it's not making full use of the potential of the methanol. At idle this low compression gets even worse because of two things. The first is that there's far more time for any mixture to escape out of the exhaust port so compression really only begins when the port closes (this still happens at full throttle but to a far lesser extent). The second is that the actual volume of air drawn in to be compressed has been drastically reduced by the throttle. So at idle you're running a really low actual compression which suits nitro better than methanol.

With the better designed (in my opinion) European engines with higher compressions you can get a fantastic idle on zero nitro. A couple of weeks ago I had an MDS 78 idling at 1400 revs although that was on the verge of stopping. A couple hundred more revs and it was absolutely stable and smooth. With an Enya 60X that I'd raised the compression by a huge amount it had an extremely smooth and low idle (on zero nitro) but the idle mix had to be leaned a great deal from where it ran the best with the standard compression.

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RE: What nitro percentage in a 2 stroke? - 11/1/2006 3:27:43 AM   
fadi81



Posts: 268
Joined: 9/11/2006
From: Luxembourg, LUXEMBOURG
Status: offline 		Thanks Downunder for your explication. But what about Japanese designs? OS for instance, are they built to American standards?
It's true I feel that my OS 46AX doesn't have lots of compression, especially when hot

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RE: What nitro percentage in a 2 stroke? - 11/1/2006 7:40:40 AM   
XJet


 

Posts: 3454
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: offline 		My 2-strokes (mainly Thunder Tigers) idle *beautifully* on 5% nitro -- in fact somtimes, when I've got my throttle cut set a little high, they'll idle at such a low speed you can almost see the blades of the prop turning (damn -- I want them to stop when I hit throttle cut :-)

I've played around with various nitro levels in fuel and found that the difference between 5% and 10% on my engines is pretty marginal. I actually got a *lot* more improvement (over 600RPMs) by switching oils rather than bumping up nitro.

Dumping CoolPower gave me thse extra revs, an even lower idle and noticeably decreased running temps.

Yay!

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RE: What nitro percentage in a 2 stroke? - 11/1/2006 7:58:12 AM   
fadi81



Posts: 268
Joined: 9/11/2006
From: Luxembourg, LUXEMBOURG
Status: offline 		Thank you for your inputs guys.
I see we are slowly settling on a 5% or 10% preference. Please keep voting for more accurate result

I agree on the oil change!

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RE: What nitro percentage in a 2 stroke? - 11/1/2006 2:03:53 PM   
Sport_Pilot



Posts: 7718
Joined: 1/21/2002
From: Acworth, GA, USA
Status: offline 		Bad poll, because the answer is dependant on the engine. Most sport engines need 10 to 20% to run best. Some can't run on anything but 0%, and others may not idle well on less than 20%.

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RE: What nitro percentage in a 2 stroke? - 11/1/2006 2:07:50 PM   
downunder



Posts: 3193
Joined: 10/10/2002
From: Adelaide, AUSTRALIA
Status: offline
quote:

ORIGINAL: fadi81
OS for instance, are they built to American standards?

Yes, the OS are built down to American standards but some of the older engines were very good compression wise. I've got several OS VF's and they're up around the 12:1 mark. I haven't checked everything of course but I guess you could say that anything made in China, Taiwan, Japan will all have fairly low compression. Super Tigre and Rossi are what you might call medium high at about 11:1 but that's on the particular engines I've got.

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RE: What nitro percentage in a 2 stroke? - 11/1/2006 5:34:50 PM   
Sport_Pilot



Posts: 7718
Joined: 1/21/2002
From: Acworth, GA, USA
Status: offline
quote:

Yes, the OS are built down to American standards but some of the older engines were very good compression wise
.

Don't you mean very bad? Compression too high? I have a ASP Red Hed with very very bad compression ratio, won't run on anything greater than 5% nitro.

< Message edited by Sport_Pilot -- 11/1/2006 5:36:38 PM >

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RE: What nitro percentage in a 2 stroke? - 11/2/2006 12:18:50 AM   
downunder



Posts: 3193
Joined: 10/10/2002
From: Adelaide, AUSTRALIA
Status: offline
quote:

ORIGINAL: Sport_Pilot
Don't you mean very bad? Compression too high? I have a ASP Red Hed with very very bad compression ratio, won't run on anything greater than 5% nitro.

That depends on your point of view. If low compression allowing lots of nitro is good then a Fox 35 with a compression of 6:1 must be a world beater . If high compression and using cheap fuel can give the same power then I know which way I want to go .

My son has a .28 buggy engine with 7.2:1 compression for high nitro, we modded the head up to 12.4:1 so he could use straight 80/20 (castor) fuel and it's now got the same performance as the others with identical buggies using nitro. They like doing a drag race along the main straight which is a good indicator.

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RE: What nitro percentage in a 2 stroke? - 11/2/2006 8:04:48 PM   
Sport_Pilot



Posts: 7718
Joined: 1/21/2002
From: Acworth, GA, USA
Status: offline
quote:

If low compression allowing lots of nitro is good then a Fox 35 with a compression of 6:1 must be a world beater.


They do gain a lot of power with lots of nitro. But the 424 break point gets trickier. Have to get the needle closer to the break point and then it runs hot. Good for sport though. If you don't mind short but faster runs.

If you take an engine built for low nitro, raise the compression ratio, especially if you keep the proper squish band, then it will gain a lot of power over the 0 percent version. Don't get me wrong I have a 0% engines and except for the fact I have to mix my on fuel, they run great. In the application I was using it for, a .90 in a .60 sized plane I didn't need more power, so why spend more on fuel?

Sometimes the idle needles are a bit sensitive with low nitro. Because they are not made to use such small amounts of fuel the ideal setting is a bit hard to find. Engines made for low nitro seem to take larger turns of the low speed needle for the same adjustment.

< Message edited by Sport_Pilot -- 11/2/2006 8:12:20 PM >

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RE: What nitro percentage in a 2 stroke? - 12/16/2006 2:35:51 PM   
d_khaw


 

Posts: 10
Joined: 12/16/2006
From: Port Moresby, PAPUA NEW GUINEA
Status: offline 		Hi Downunder
How do you increase the compression of an engine to suit 80/20 fuel? I live in PNG and cannot get nitro. Is this a matter of removing the shim in the engine head?

Rgds
Daniel in PNG


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RE: What nitro percentage in a 2 stroke? - 12/24/2006 11:57:58 AM   
speedster 1919



Posts: 1467
Joined: 12/17/2004
From: Martinsville, IN, USA
Status: offline 		Ok Xjet I'll bite which oil gave you 600 more RPM. And did you change the % at the same time?

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