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Higher Nitro amount = more power?

Old 03-14-2014, 10:53 AM
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yak86
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Default Higher Nitro amount = more power?

I have two evo 36nt on a b-25 and the manual sayings 5%-30% nitro, i normally run 10-15% in most of my engines. would upping the nitro amount give that much more power? I'm assuming that upping the nitro amount runs the engine hotter and you will need more air flow.

Anyone do rpm sheet with nitro amounts?
Old 03-14-2014, 11:33 AM
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speedracerntrixie
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No two different make engines will react to an increase in nitro quite the same so some kind of spread sheet showing % power increase per % of nitro is just not practical. I'm surprised that they give such a large range, that tells me that the EVO brand is not set up with as much compression as I originally thought. In a glow engine the nitro content, compression, plug heat and load all contribute the timing of the ignition or at what point in the rotation the bang happens. If you run more nitro then what the compression ratio will allow, you end up with pre-ignition. More compression = less nitro. Not only does this tear up the engine, it will create less power in the process. To get the most out of any engine, you need to match the nitro content, plug heat and prop size. Difficult to know where to start as you did not state your prop size and make, muffler and what brand of fuel you are using. Without knowing this it really is difficult to say if moving to more nitro then 15% would get you anything. As far as cooling is concerned, fuel manufacturers usually up the oil content along with the nitro. I have never had to do any additional cooling mods when upping nitro. With more info I may be able to offer more help.
Old 03-14-2014, 05:25 PM
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blw
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The Evolutions that I have or have seen all like nitro. I have a 36 that I haven't run yet. From all reports, Evos need hot plugs like an A3. A general rule of thumb is a max increase of 300 rpm going from 15% to 30% if you're lucky. They are good engines.
Old 03-19-2014, 07:48 AM
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Hi!
5-15 % nitro is just fine! Going up to 30% is just going to add more heat and only increase rpm slightly, It will not add reliability!
A much better way (cheaper) is to remove the head shim! Doing so you can just get as much power on 5% nitro as on 30%.
Old 03-19-2014, 07:58 AM
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I found that an Evolution PTS .455 I bought used has been running on 15% all this time with the shims removed. I know the 46 will take a lot of nitro. I'm going to take out the 2 shims the next time I run that engine. These engines seem to like 30% (and higher), and higher compression. You do need to run an A3 plug in them. They won't burn the fuel efficiently on anything cooler. I don't know why Horizon doesn't use those in the first place. I've seen owners struggle with the cooler plugs that come with the engines.
Old 03-19-2014, 10:26 AM
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BLW The reason that Horizon does not include the A-3 plug is because it is OS and part of their main competitor, Great Planes.
Old 03-19-2014, 11:36 AM
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I'm assuming that upping the nitro amount runs the engine hotter and you will need more air flow.
It will run hotter if the compression is too high, the plug is too hot, the mixture is too lean, or the prop is too big. All of these affect the timing, but if the timing is right and especially if it is on the rich side a high nitro engine will run cooler than on methanol. If you look at the nitro dragsters and funny cars they have no radiators. They are running on so much nitro and at a very rich mixture so that they do not need water cooling nor air cooling. The fuel is not even vaporized well and the wet fuel evaporating from the cylinder walls is all that is needed to keep them cool. Now if you run it lean it will run hotter than a lean mixture of methanol, but it will not make the most power with the lean mixture.

Also though the RPM increase seems small the torque is also higher because it takes more torque to spin a prop faster. So the power you will notice will be much higher than the percentage of RPM increase.
Old 03-19-2014, 12:10 PM
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speedracerntrixie
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Agreed, properly set up more nitro will not produce more heat. I think it's an old modelers tale that started from guys simply pumping more nitro without taking compression , plug heat or load into consideration.
Old 03-19-2014, 01:19 PM
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Paul, I think they are still shipping with Hangar 9 plugs. Still, it's a big performance gap.
Old 03-19-2014, 01:55 PM
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Granpooba
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For the life of me, I can not remember where I came by this bit of information, but read someplace where a lot of flyers are switching to 30% Helicopter Fuel. They state that it increases power, while providing increased lubrication.

Don't really know how true the statement was, but hopefully somebody will come along to confirm or disclaim the statement.
Old 03-19-2014, 05:50 PM
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Confirmed, a few years ago Horizon was pushing Coolpower 30/30 heli fuel for the larger displacement Saito 4 strokes. I have a buddy that had a Ohio R/C 84" Extra 300 with a Saito 300 twin that ran the 30/30. That engine sounded great, bump started and pulled that airplane great. Problem was it was 40.00 in fuel every trip to the field. The Saito eventually gave way to a ZDZ 40.
Old 03-19-2014, 08:28 PM
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Agreed, properly set up more nitro will not produce more heat.
Actually it does produce more heat, but at a lower temperature.
Old 03-20-2014, 12:02 AM
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Originally Posted by MrMotor
BLW The reason that Horizon does not include the A-3 plug is because it is OS and part of their main competitor, Great Planes.
OS plugs are too expensive and overrated anyway. There are better options for less money IMHO.
Old 03-20-2014, 12:38 AM
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flycatch
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Originally Posted by Granpooba
For the life of me, I can not remember where I came by this bit of information, but read someplace where a lot of flyers are switching to 30% Helicopter Fuel. They state that it increases power, while providing increased lubrication.

Don't really know how true the statement was, but hopefully somebody will come along to confirm or disclaim the statement.
It came from Saito and I tried it. You pick up 300-450 rpms however you most retune running richer. Flight time is shorter so you decide.
Old 03-20-2014, 12:40 AM
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flycatch
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Originally Posted by 1QwkSport2.5r
OS plugs are too expensive and overrated anyway. There are better options for less money IMHO.
OS plugs are more expensive because they use pure platinum for the heating element.
Old 03-20-2014, 01:42 AM
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Originally Posted by Sport_Pilot
It will run hotter if the compression is too high, the plug is too hot, the mixture is too lean, or the prop is too big. All of these affect the timing, but if the timing is right and especially if it is on the rich side a high nitro engine will run cooler than on methanol. If you look at the nitro dragsters and funny cars they have no radiators. They are running on so much nitro and at a very rich mixture so that they do not need water cooling nor air cooling. The fuel is not even vaporized well and the wet fuel evaporating from the cylinder walls is all that is needed to keep them cool. Now if you run it lean it will run hotter than a lean mixture of methanol, but it will not make the most power with the lean mixture.

Also though the RPM increase seems small the torque is also higher because it takes more torque to spin a prop faster. So the power you will notice will be much higher than the percentage of RPM increase.
There are more things to consider here. You can't compare a top fuel dragster to a model engine just because they both run nitro.

Dragsters and funny cars are designed to run for a very short time, the engine internal parts have very different tolerances and in most cases their engines are rebuilt between races.

It's like chalk and cheese.
Old 03-20-2014, 01:47 AM
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Originally Posted by speedracerntrixie
No two different make engines will react to an increase in nitro quite the same so some kind of spread sheet showing % power increase per % of nitro is just not practical. I'm surprised that they give such a large range, that tells me that the EVO brand is not set up with as much compression as I originally thought. In a glow engine the nitro content, compression, plug heat and load all contribute the timing of the ignition or at what point in the rotation the bang happens. If you run more nitro then what the compression ratio will allow, you end up with pre-ignition. More compression = less nitro. Not only does this tear up the engine, it will create less power in the process. To get the most out of any engine, you need to match the nitro content, plug heat and prop size. Difficult to know where to start as you did not state your prop size and make, muffler and what brand of fuel you are using. Without knowing this it really is difficult to say if moving to more nitro then 15% would get you anything. As far as cooling is concerned, fuel manufacturers usually up the oil content along with the nitro. I have never had to do any additional cooling mods when upping nitro. With more info I may be able to offer more help.
I always mix my own fuel. I use the same oil content regardless of nitro % and have never had cooling problems.
Old 03-20-2014, 02:33 AM
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The oil provides very little cooling effect on the engine despite popular belief as well.
Old 03-20-2014, 03:44 AM
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Originally Posted by flycatch
OS plugs are more expensive because they use pure platinum for the heating element.
They do not use pure platinum, and they would not last long if they did! Almost all manufactures use an alloy of platinum and rhodium.
Old 03-20-2014, 03:46 AM
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Dragsters and funny cars are designed to run for a very short time, the engine internal parts have very different tolerances and in most cases their engines are rebuilt between races.

Sure you can, though they run for a short time they can run at low power for a very long time without overheating. In fact they will run them for more than several minutes in the pits to set in the new rings.
Old 03-20-2014, 04:27 AM
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Originally Posted by Sport_Pilot
Actually it does produce more heat, but at a lower temperature.
Coffee before RCU.............
Old 03-20-2014, 04:28 AM
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Originally Posted by 1QwkSport2.5r
The oil provides very little cooling effect on the engine despite popular belief as well.
Try running an glow engine with 10% oil and then tell me how it ran at the same temp.
Old 03-20-2014, 04:31 AM
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Yes, in a well set up pattern plane that only sees short bursts of full throttle and extended down lines at idle. Most sport pilot fly around at much higher throttle settings. They also don't have the power reserve you do so will tend to needle closer to max RPM.
Old 03-20-2014, 04:58 AM
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I had my coffee, heat and temperature are not the same thing. You can have more heat with a lower temperature. Heat a pound of water 10 degrees and you have 10 BTU of heat, Heat a hundred pounds of water 1 degree and you have 100 BTU of heat. The latter is what nitro is doing. More pounds of fuel and air, not just a little but a lot, but the temperature does not rise as much. It helps that nitro is a lot denser than water and air, and that it is a monopropellent.
Old 03-20-2014, 05:19 AM
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Originally Posted by Sport_Pilot
I had my coffee, heat and temperature are not the same thing. You can have more heat with a lower temperature. Heat a pound of water 10 degrees and you have 10 BTU of heat, Heat a hundred pounds of water 1 degree and you have 100 BTU of heat. The latter is what nitro is doing. More pounds of fuel and air, not just a little but a lot, but the temperature does not rise as much. It helps that nitro is a lot denser than water and air, and that it is a monopropellent.

Not too sure I'm on the same page. We really aren't running a larger volume of fuel and air, more like running a fuel with a slightly lower flash point and more volatile thus bigger bang that depending on other influences will advance the combustion timing. To increase air we would have to do mechanical mods or up RPM. It could be argued that higher nitro will automatically lead to more RPM but some are using the nitro to run a larger prop at the same RPM. Either way more nitro leads to more power provided all the other things that influence the ignition timing are in check as well.

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