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Honda MX & Off-Road Dirt Bikes
what would cause the header to glow red
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[QUOTE="Rich Rohrich, post: 1409702, member: 16241"] You're off the track and headed for the weeds. :) Honda is using knock sensor technologies similar to those being used in the automotive industry, it's just tuned very specifically to the frequency range that will be present in the RS125 and RS250 two-stroke engines. The Knocking sound you hear when an engine is experiencing abnormal combustion is the result of a rapid pressure rise in the cylinder. Unburned mixture and the end gases at the edges of the combustion chamber are being raised to extremely high temperatures as the advancing flame front compresses and heats up the mixture directly in front of it. This activity before the flame front reaches the end gases at the edge of the chamber are sometimes called pre-flame reactions. The longer it takes for the complete burning to take place the greater the chances that these pre-flame reactions will force the end gases to reach the auto ignition point and cause a rapid uncontrolled pressure rise, along with a huge increase in cylinder temperature. If brought to the auto ignition point the end gases of the combustion chamber can cause a pressure and frequency rise that is high enough to be audible. That's the KNOCK or PING that you hear. Ideally, the burning of the mixture will be completed before any of these end gases have an opportunity to reach the point of auto ignition. It's important to remember that the air/fuel ratio that produces the best power also tends to have the best chance of knocking. Running on the rich side of best power on a two-stroke tends to cool the piston crown and minimize knock, but go too far and the power drops quickly. Honda is measuring REAL spark knock aka detonation, not some mythical micro detonation. In 125 GP roadracing every little bit of power matters. So what Honda is doing is measuring real spark knock, not to stop it completely, but to find the [b]minimum[/b] amount of knock that will produce best power and still allow the engine to finish a race. We tune two-strokes that way at the drag strip. Much like drag racing, pistons are treated as disposable commodities in two-stroke GP racing. Dirt riders have to tune much more conservatively for their application. As you get comfortable reading plugs, piston crowns, and cylinder heads you can see traces of knock that might not always be heard by a rider. The problem is that can take years to master. Using a device that can detect the number of times a high frequency pressure spike occurs in the combustion chamber is much more reliable than all but the most expert of tuners. Most riders have to just tune to the safe and slow side. Devices like Honda designed can get the average racer closer to an optimized package without the usual learning curve that destroys a lot of parts along the way. I hope that answered your question. ;) [/QUOTE]
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Honda MX & Off-Road Dirt Bikes
what would cause the header to glow red
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