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-   -   Nitro Percentage (http://www.rcuniverse.com/forum/car-nitro-gas-engines-269/11552237-nitro-percentage.html)

PearlDrumsRule 06-24-2013 03:51 PM

Nitro Percentage
 
I know that there are different percentages of nitro. What will happen if I change from 20% nitro to 30% nitro? I know that I will have to re-tune but can I switch between 20% and 30% and just retune each time?

downunder 06-24-2013 06:40 PM

RE: Nitro Percentage
 
So long as you retune you can switch between any nitro percent all the way from zero nitro to whatever you like. With an extreme change you may need to use a different heat range plug though for best performance.

nitrosteve22 07-02-2013 12:49 PM

RE: Nitro Percentage
 
Stupid Q, does it have to be a larger displacement engine to run higher percentage? I've never ran anything over %20 but I have an old vx .18 with a couple cold plugs and I'd like to run some seriously high %... Just mainly to see what happens I guess.... Thanks.

1QwkSport2.5r 07-02-2013 01:12 PM

RE: Nitro Percentage
 
Engine displacement has no bearing on how much nitro you use. Using more than 30% nitro most likely will require shimming the head higher reducing the compression ratio. Colder plugs help but may not be the end-all.

If you blow plugs, you're using too much nitro or the plug isn't cold enough. If its a cold plug to start with, back off on the nitro until it quits blowing plugs.

rccheech 07-03-2013 07:43 AM

RE: Nitro Percentage
 
Most engines are set to use up to 30% nitro content, anything higher and you want to add shims to prevent detonation. After about 30% nitro, you will not notice any difference on power, even the switch from 20% to 30% will not have much of a noticable difference.

supertib 07-03-2013 09:37 PM

RE: Nitro Percentage
 

Quote:

ORIGINAL: rccheech

Most engines are set to use up to 30% nitro content, anything higher and you want to add shims to prevent detonation. After about 30% nitro, you will not notice any difference on power, even the switch from 20% to 30% will not have much of a noticable difference.

I have to disagree here to some degree...switching from 20-30% can make a very substantial difference in many engines..... In a tuned offroad .21 the difference from 20% to 30% is huge...Engines will run cooler, have broader tuning window, have stronger throttle response, and more then a noticeable increase in overall power............ However it all comes down to wehter or not the engine is optimized for the fuel.....a poorly setup engine probably wont run much stronger on 30% then it would on 20%.......However on a properly setup engine the performance difference between 20% and 30 % is massive.......hell the difference between 7% oil and 12 % oil is ridiculous........

1QwkSport2.5r 07-04-2013 07:57 AM

RE: Nitro Percentage
 
Determining the compression ratio will give you a good indication of how much nitro you can use without causing detonation, that is if you really want to get technical. I do agree with Neal in respect to some engines will respond much better to more nitro, namely going from 20% to 30% being a noticeable increase. I've seen engines with trapped CR anywhere from 8:1 to 12:1. The engines running 10-12:1 will run well on low nitro fuel (0-10%) and may detonate on more than 10% whereas an engine with a CR of 8-10:1 will probably run 30-35% fine. I think even beyond 35% at 8:1 CR you will still need to shim the head a little bit and/or run a cold plug.

Lowering the head (taking out shims) will increase power but will reduce longevity to a point. It can also limit the amount of nitro you can use. In a lot of cases, the shim is only installed to control the CR and not to seal the head/head button to the cylinder liner. One can use a 4-stroke glow plug to increase the compression ratio as well as those have a projected tip that extends into the combustion chamber further. I've done experiments using a 4-cycle glow plug and removing the head shim and getting really reasonable performance running without any nitro at all. (Yeah, I'll go outside my comfort zone from time to time and run zero nitro.)

For the average modeler, I'd just keep adding nitro until you blow plugs. Once you blow a plug or two, either shim the head .1-.2mm, run a colder plug, or drop the nitro content a little.




Anthoop 07-04-2013 09:15 AM

RE: Nitro Percentage
 

Quote:

ORIGINAL: supertib
However on a properly setup engine the performance difference between 20% and 30 % is massive.......hell the difference between 7% oil and 12 % oil is ridiculous........
I would expect changing oil content from 12-7 would have a greater peformance difference than a 10% nitro change on any engine that can take it. The oil only lowers the performance potential of the fuel...but then you know that.. ;)


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