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20% Nitro Vs. 30% Nitro Pro's and Con's

20% Nitro Vs. 30% Nitro Pro's and Con's

Old 04-01-2010, 06:06 PM
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Default 20% Nitro Vs. 30% Nitro Pro's and Con's

I just received a bottle of 30% nitro fuel from ebay. I originaly ordered 20%

I was going to break-in my axail .28 on my Savage with it. Its a brand new engine. My son also has a T-maxx 2.5 that we run 20% in.

So I guess my questions are:
Can I break my motor in on 30% fuel?
Is there anything I need to do to the t-maxx to run the 30%? (head shims?)

What are the benefits of running 30% over 20%?

Any suggestion and info will be appreciated Thanks
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Old 04-02-2010, 05:43 PM
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Generally speaking, when going from 20% to 30% nitro, you need to add a head shim. The 2.5R can handle 30% as it comes from Traxxas, so you're good there. At most, you may need to go to a one step colder plug, but that will be preference more than anythng else. If you don't run your motor super-lean, then don't worry about it.

The 30% nitro will give you more power, but narrow your tuning window slightly (not so much where it's a problem though). Personally, I run 30% in all of my nitro cars, but that's preference too. I would suggest this though....if you break the motor in with 30%, you should stay with 30%. You'll get conflicting viewpoints on that, but I'd rather be safe than sorry.

Just to ease your mind on the T-Maxx...I changed from 20% to 30% after I had about a gallon on my 2.5R. It didn't cause any problems with the motor.

In case you hadn't already seen this, here's a link: http://www.rchobbies.org/cars_eng-tuning.htm It's a very informative article, and has a paragraph specifically related to changing nitro content.
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Old 04-02-2010, 09:22 PM
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Thanks for the reply Stubbs,
Does it make a difference if the traxxas motor is 2.5 and not the 2.5r?

I've also heard that running a higher nitro percentage will produce cooler temps.
any truth to that...
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Old 04-03-2010, 08:49 AM
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Originally Posted by Big Midget
Thanks for the reply Stubbs,
Does it make a difference if the traxxas motor is 2.5 and not the 2.5r?

I've also heard that running a higher nitro percentage will produce cooler temps.
any truth to that...
Nitromethane does offer about double the cooling through evaporation than methanol, that combined with a larger fuel volume from the richer settings required will cool slightly better.
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Old 04-03-2010, 09:00 AM
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Good info from mr. stubbs, however, I wouldn't say you necessarily need to add a shim to run 30%. Part of the idea behind adding the shim is to control timing, which you can do (to a degree) by varying the glow plug's heat range. The timing will advance with an increase in nitro content. If you can't retard the timing enough to avoid detonation/overheating with a change of plug, then you'll have to re-shim the head.

Originally Posted by Big Midget
I've also heard that running a higher nitro percentage will produce cooler temps.
any truth to that...
Well...take 2 identical motors (no such thing), one running 20% and the other 30%. The motor running 30% can be tuned to run much cooler and still produce the same, or better, performance than the motor running 20%. Of course, most people will still be inclined to lean either motor out to max performance levels, and test the motor's boundaries of detonation/heat tolerance.
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Old 04-03-2010, 12:26 PM
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Unless your racing and got a good handle on tuneing your not gonna notice the extra 10% you can get plenty of power out of 20% with a good tune but if you have 30% its not gonna hurt you any I would use a Med plug like a OS#8 and tune a little on the rich side. rember rich dosnt hurt anything. Lean,Detonation and high heat kills motors
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Old 04-04-2010, 05:23 PM
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Originally Posted by helibrian
Good info from mr. stubbs, however, I wouldn't say you necessarily need to add a shim to run 30%. Part of the idea behind adding the shim is to control timing, which you can do (to a degree) by varying the glow plug's heat range. The timing will advance with an increase in nitro content. If you can't retard the timing enough to avoid detonation/overheating with a change of plug, then you'll have to re-shim the head.



Well...take 2 identical motors (no such thing), one running 20% and the other 30%. The motor running 30% can be tuned to run much cooler and still produce the same, or better, performance than the motor running 20%. Of course, most people will still be inclined to lean either motor out to max performance levels, and test the motor's boundaries of detonation/heat tolerance.
I was speaking mainly of the high end race motors that come from the factory shimmed to run 30%. To get sufficient power out of 20%, you generally remove the head shim. Then if you go back to 30%, and don't put it back on, you can risk detonation.

The 2.5 / 2.5R has a shim in it from the factory, so you can run 30% no problem. If however, you removed it to run 20%, put it back in to be safe. Like helibrian said, you can vary timing with glow plug, but you'll be limiting the range that you can work within if the motor isn't shimmed properly to begin with.

Last edited by Stubbs; 04-05-2010 at 07:58 PM. Reason: typos...
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Old 04-04-2010, 05:24 PM
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Originally Posted by Big Midget
Thanks for the reply Stubbs,
Does it make a difference if the traxxas motor is 2.5 and not the 2.5r?

I've also heard that running a higher nitro percentage will produce cooler temps.
any truth to that...
The main difference between the 2.5 and 2.5R is the cooling head, and some minor tweaking inside the motor.
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Old 04-04-2010, 08:28 PM
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Thanks again guys, So is it just trail and error to determine if the motor is shimmed correctly?

whats your guy's opinions on motor break-in.

I've ran about a half tank of fuel through the engine. My hottest temps have been between 280-285 and climbing some (I've richend the HSN about an hour and a half out from the factory settings) before I shut it down. I think this is to hot.
I'm under the impression that a motor will run at the
temps it was broke-in at, any truth to that?

I was told to idle my first 3 tanks of fuel from a very reliable source then follow a few other steps for the rest of the break-in but I think I need to get some air flow.

Can anyone suggest a good break-in procedure, the motor is an axail .28 I'm running an R-5 plug.
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Old 04-05-2010, 03:32 AM
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Originally Posted by Big Midget
Thanks again guys, So is it just trail and error to determine if the motor is shimmed correctly?

whats your guy's opinions on motor break-in.

I've ran about a half tank of fuel through the engine. My hottest temps have been between 280-285 and climbing some (I've richend the HSN about an hour and a half out from the factory settings) before I shut it down. I think this is to hot.
I'm under the impression that a motor will run at the
temps it was broke-in at, any truth to that?

I was told to idle my first 3 tanks of fuel from a very reliable source then follow a few other steps for the rest of the break-in but I think I need to get some air flow.

Can anyone suggest a good break-in procedure, the motor is an axail .28 I'm running an R-5 plug.
I presume your side is cold there...?

The idling break-in method was actually causing more wear to a glow engine...

Here's a link on the heat-cycle break-in method:
http://www.youtube.com/watch?v=kPcXd-2-EEA
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Old 04-05-2010, 04:40 AM
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Definitely COOLER temps with 30%. Tuning window is larger IMO. 30% in everything makes life easier.
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Old 04-06-2010, 10:54 AM
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Originally Posted by Big Midget
whats your guy's opinions on motor break-in.

I've ran about a half tank of fuel through the engine. My hottest temps have been between 280-285 and climbing some (I've richend the HSN about an hour and a half out from the factory settings) before I shut it down. I think this is to hot.
That's probably a bit hotter than you want with a new engine, but it's not the end of the world. I have a picco .26 that I broke in @ ~300 about 6 years ago. Its had well over 20 gallons through it and still runs very very strong.

Hate to give break-in advice over the internet, but I will say the following....everyone's got their own variations on break-in, but on the safe side, I'd recommend fattening up the top and bottom end to the point that the exhaust is spitting plenty of oil. The way that looks will vary a bit from setup to setup, but generally, you want it to spit so much out that if you leave the truck in one spot for a period of time, a puddle will form under the exhaust tip. The reason for this is, the excess fuel will flush out any aluminum (or other;. chrome, brass, bronze, etc.) particles that will be shaven from mating surfaces in the engine during break-in. The engine will probably bog a bit under throttle as if it's....well.....running very rich. On the other hand, I've seen people run their engines so rich after break-in, that the resulting hydraulic pressure leads to premature engine failure.

You said 1 hour and 1/2. That's 3/24ths of a turn. That's nothing huge for the axial .28. With that particular carb/engine setup, if everything else is right, I use very liberal turn increments initially, and fine tune only after I'm in the ballpark. Don't be afraid to richen that needle in large increments. You can always go back. It's the leaning direction where you want be more conservative with the screwdriver.

Originally Posted by Big Midget
I'm under the impression that a motor will run at the
temps it was broke-in at, any truth to that?
Not necessarily. There are many variables that will effect temps, so that's going to depend on how you go about setting it up.

BTW;
Did you seal that engine before you installed it?
Does it sound like it's detonating at all?
With the cold plug you're running, if the timing's too advanced, you may wind up having to shim.
Also don't feel as if you're stuck with 30%. Buy yourself a bottle of 10/15/20%, mix it with some of the 30% to make 15/20/25/27.1825000% or anything in between.
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Old 04-06-2010, 08:30 PM
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I read and checked out the links that you guys posted. I decided to follow the break-in procedure from the engine's manual.

I richend the top end a quarter turn. It was a little cooler outside yesterday but my temps got no hotter than 220 degree's. I idled though 2 tanks of fuel and have a nice oily spot in my drive way

I drove the truck through 2 tanks of fuel hitting about 1/4 throttle then letting the truck coast a bit. On my third tank of driving the truck, I got closer to 1/2 throttle then coasting. I could feel the engine loosening up a bit. Still my temps stayed cool around 205 to 210. I'm still on my 3rd tank of fuel. I'm happy with my temps so far. I had to lean the top end some to get the truck to move but I did in small 1/8 turns increments being careful not to over do it.

I didn't seal the engine before I installed it.
Its was brand new, Should I have sealed it anyway?
It didn't sound like it was detonating, if it was I should see some pitting on top of the piston, right......
Also should I stick with the R-5 plug?

So far I'm happy with the 30%. The Fuel I'm using is Torco, anyone familiar with this brand? any opinions on it?

Thanks again for the helpful info, the first link was quite helpful I'm plan on using it as a reference tool in the future.
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