![]() It also might vary from motor to motor depending on how efficient the cylinder head is, where the spark plug is located, the nominal compression ratio, and many other parameters. Well, clearly I don't have an answer to this one though I'm sure there are plenty of folks who do. On the other hand (anticipating the disagree view), if spark happens too soon perhaps not enough compression will have occurred to make the conditions necessary to propagate a good flame throughout the combustion chamber - or worse yet you might have a misfire - and so perhaps we should make that spark happen a bit later after the piston has moved further up the bore and a bit more compression has occured. But whatever it's called let's agree (or not) to make that spark start sooner to compensate for the slower fuel burn rate. Tomorrow I'll probably call it retarding the spark because I'm moving the ignition point further away from TDC. Today I'll chose to call that advancing the spark since it will happen sooner. My suspicion is that it will since static compression will be lower and the fuel will burn more slowly - therefore you probably want the spark to occur a tiny bit earlier. Whether or not changing the ignition point will help at altitude, well that's an entirely different issue. If you think otherwise please explain in terms a horseshoer can understand and we'll evaluate it from that perspective. When a spark occurs, or indeed even if no spark occurs, doesn't alter this situation one wit. The piston comes up the bore, the valves close, and compression occurs. "playing with timing doesn't change the compression ratio in any way shape or form" In any case, since we can't dick with the timing on our bikes anymore, who cares! We are both actually saying the same thing as long as we agree that firing closer to TDC is what increases the performance when at a higher altitude. This is the same with retard/advance jargon, some will say advance the timing and mean with respect to the spark, while others mean with respect to TDC. However, another may say I am getting further away from my position. As an example, if I am walking towards you someone make think I am getting closer to your position. Hence you get better performance on your power stroke than if you did not make the timing adjustment.Īgain the perspective issue of retard/advance is the only thing we differ on. Which is: Firing the spark plugs so that you are closer to TDC, when at altitude, increases your compression ratio so that you get closer to the design compression ratio. No, you are not on drugs And since it's the 2nd of January, we are probably no longer drunk.Īll of the links I posted say exactly what I said. no matter when or where you ignite the bomb, it pushes back at 9.5/1 depending on the ambient air pressure of your locale. Playing with timing doesn't change the compression ratio in any way shape or form.at best it only changes the ignition point under compression, and wouldn't gain anything beyond the stock 9.5/1 other than inhibit performance. ![]() If you want more air to compress, look at a blower, shave the heads, or increase the stroke. Stand on your head, it's still a 9.5/1 CR from the bottom of the sea to Mt Everest. your scenerio doesn't change the compression ratio since it's based on ambient to compressed. I think you're confusing compression ratio with ignition point. The compression at elevation will at best reach somewhere below design specs. The additional compression of course gives you a more efficient power stroke. > additional compression is needed since at the higher altitude the intake air pressure is lower (and hence at a lower density). Not more air, same air volume under higher compression at the ignition point > This allows the piston to compress more air before the spark fires. You advance the timing to delay the spark.Īdvance is earlier retard is later.forget semantics and do it this way for universal would be short sighted to think we're all stupid and inexperienced.
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