Seisick

I have several friends that live at 2500meters above sea level that have purchased sirio evo2, rossi black pixy several novas but they all have been having problems adjusting the needles to obtain some performance at least near at the sea level but nothing, and I mean nothing has worked, even adjusting the middle needle did not give any good result, any advise?

SlobbaTech

Run higher nitro content fuel to "replace" some of the air you lose that high up.

afm

What you have to do is add more shims to the combustion chamber.
To use let's say 25% Nitro in a zone betwen 0 and 1,000 mts. a good base is to have a combustion chamber between 0.48 and 0.55 mm. For more Nitro you'll need more chamber height.
As a reference I'll say that for 16% Nitro (allways at a height between 0 and 1,000mts) the chamber should be between 0.38 and 0.40mm. With these data you can calcultae a scale to adapt it to your conditions.

AFM

dino.tw

Sorry,....but are you sure "add" more shims???

The density of air(or you can say oxygen) is less and less with altitude. So the compression should be less at high altitude with the same shims...that is what I knew sorry bro.

afm

You are right Dino, but i made my comments because somebody suggested to use 30% Nitro. So lets restate all, asuming you are going to use same Nitro contents.
For high altitude you need to advance ignition timing, which can be done either with a hotter plug, or reducing combustion chamber (less shims),but you'll have to compromise or you'll loose top end or low end.
IGNITION TIMING FACTS

· You advance ignition with a hot plug, which will give you more torque or low speed
· You retard ignition with a cold plug, which will give you more rpm’s or top speed

The above is true in both cases if you have the same compression ratio (combustion chamber shimming), and use the same nitro % on fuel.

But if you change compression ratio (combustion chamber shimming, and or nitro %), you have to compromise.

· If you increment compression (smaller combustion chamber = less shims) you are advancing timing, thus incrementing torque, so you will need to put a colder plug to compensate for top end., and more generated heat, which could cause pre-ignition.
· If you reduce compression (bigger combustion chamber = more shims) you are retarding timing, thus incrementing top speed, so you will need to put a hotter plug to compensate for torque, and less generated heat.

The ideal combustion chamber for .12 engines at sea level is:

· For 16% nitro = .015 inch or 0.381 mm
· For 20% nitro = .016 inch or 0.410 mm
· For 25% nitro = .018 inch or 0.457 mm
· For 30% nitro = .021 inch or 0.533 mm

So you have to shim the engine accordingly to get those total combustion chamber sizes, but making a new chart considering higher altitude.

I would also suggest to contact any Mexican R/C web site, because they have a very developed market and are experts in running at high altitude

AFM

dino.tw

Seisick

running with higher nitro and using a hotter has been tried and still no good results, the funny thing is that it only happens with high end engines, with os and ae .15s that come with the tc3 rtr plus no problems at all. and hell, these engines had the same performance as my sirio evo 2 5 port.
Alfonso, any suggested mexican web page where I can find valuable information regarding the adjustments, thanks!

afm

This is what a friend driver from Mexico DF answered me about
running at high altitude:

" We run at 3,000 mts, and the main mod. we do is run with fuel at 40% nitro and cold plugs 7 or 8, In the case of JP or RB Rody tuned engines we take out original shim (0.30mm) and put two of 0.10mm, for a total of 0.20mm"

Hope this helps

AFM

Seisick

thanks, i'll pass along that recommendation to my friends, and see the results.

DerekB

For the most part you are dealing with less air and will just need to lean out the Air/Fuel mixture. There is going to be a actual drop in power output that increasing nitro precentage (doesn't add in O2) will account for. If you're racing everybody with the same fuel it won't make a difference.

For example...power at sea level is 1hp at 2500 meters it may drop to .8, but also require a leaner AF ratio to have the proper mixture. If you want to bump the power back up you can increase nitro and/or remove shims.