| Tuning By Temperature |
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| Posted on Fri 21 Oct 2005 by nitromonkey (2496 reads) |
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The simple answer to the line above is Probably Not, Here's why: A typical internal combustion engine, whether it is a 2 stroke air/fuel cooled such as an RC engine or a water cooled Hemi in your truck runs most efficiently at a certain air/fuel ratio that varies depending on the type of engine. 2 Cycle Air Cooled Engine. An RC engine relies on both air and fuel to cool it. The air flow is relatively constant and not very adjustable, so we won't even get into that here. The fuel mixture, however, is very much adjustable. Most RC engines are tuned by temperature since this is the only variable that can easily be measured, but it's not the best way to measure fuel/air ratio as mentioned above. The Myth. Many believe that you should richen an RC engine as the temperature increases and lean it out as it decreases (not necessarily so). This logic is based on keeping your engine running at a given temperature, but NOT on optimal performance. The Facts. Hot air carries less oxygen than cool air for any given volume. So, if you want to keep your engine running at the optimal air/fuel ratio as the day heats up, you should lean it out or give it LESS fuel because there is also less oxygen in the air and richen it or give it more fuel as the day cools off since the air now carries more oxygen. Have you ever noticed your real car seams to run better at night when the air is cooler and contains more oxygen? The Snag. Life with an RC engine is not that simple since the fuel is also used to cool the engine, but the theory is still correct. It is best to tune your RC engine to run relatively cool (180-190 degrees) when the outside temperature is mild, around 60-70 degrees. As the day warms up, lean the engine out to maintain performance, but don't let it run too hot (that's another story to be covered later on). In the evening as the air temperature drops, richen the engine and tune it mostly by how it performs, not mostly by temperature. The Tradeoff. During long evening mains you want to take in consideration fuel consumption to minimize fuel pit stops, so you will want to find a compromise between performance and fuel economy. During long mid-day mains in the heat, you will need to also find a compromise between performance and engine life because the leaner you run it the hotter it will run and generally will lessen the life of your engine. The Conclusion. The theory of "richer when hotter" is only based on maintaining a certain temperature, NOT on optimum engine performance. The theory of "leaner when hotter and richer when cooler" is correct for best engine performance, but there are tradeoffs as discussed above. Nitromonkey.com |
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