Retarding ignition timing11/14/2023 ![]() I am working on custom maps for our RSV250s right now and these bikes hold the highest advance value until right about 7,000-7,500 rpm. Two stroke timing maps provide the greatest amount of advance at low RPM. "At higher revs the ignition timing is more advanced because the motor is revolving quicker." If you think my edits are wrong then for christs sake let me know :p OK I've changed my mind again so I'll mark the WRONG bits :lol: thats cos I got it right and wrong in the same post. so I'm no expert and would love to hear comments on my beliefs.įinally if you have a link to that article i'd love to read it :) my pa is a mechanic and I have rebuilt various holden and BMW motors. Remembering that increasing peak power increases the load on various components (including rings!) and should be taken into account.Īlthough I grew up in a garage at times I'm all thumbs when working on my vehicles. So in short you may be able to extend your power a little at both ends of the spectrum, and the easiest way would be aftermarket pipes/chip. once again before any percieved benefits in extra scavenging. Also if timing is too far retarded *(should be advanced)*combustion will occur before TDC and you will put a rod through the block/suffer major piston failure. Thus no matter how good any extra scavenging effect is as a result of changing timing the motor will not be producing optimum power. If timing is too far advanced *(should be retarded)*then the piston will pass TDC before combustion resulting in a loss of power, as the explosion occurs in a larger volume. Timing pulses may well effect the pressure pulse but how? at top dead centre (TDC) the ports are closed. At higher revs the ignition timing is more advanced because the motor is revolving quicker. There is an upper limit to gasoline engine bore size due to flame spread time and spark knock.Retarding the timing will indeed reduce power output (based on an optimised stock bike) all other things being equal. More swirl, higher RPM, small compact combustion chamber, centrally located spark. If the spark is too soon before TDC the pressure and temperature builds too high during the flame spread because the piston is still going up.Īnything that speeds up the flame spread and reduces the time unburned fuel-air spends at high pressure and temperature reduces the tendency to ping: Octane rating is the fuel’s resistance to this spontaneous combustion. This spontaneous burn happens much more quickly than the normal flame spread, making a ping noise and hitting all surfaces of the combustion chamber like a hammer blow. This happens to be how diesel engines work, except the fuel is gradually introduced to air that is already hot and compressed. Given enough heat, pressure and time the fuel-air mix can spontaneously burst into flame. When the flame has spread part way the remaining unburned fuel-air gets compressed and heated by the nearby flames and expanding gases (or red hot carbon deposits). The fuel-air mixture is swirling around, which helps speed up the spread of the flame. Normally, when the spark plug fires the flame spreads from the spark plug out to the farthest reaches of the combustion chamber. Here’s what happens to cause “spark knock” pinging:įirst it happens after the spark, as opposed to pre-ignition or detonation. In other words, preignition can’t cure preignition. So you can see that you can’t stop preignition by advancing the timing. A black cloud would appear behind me and the pinging would stop until I drove on base for a couple of days. I would then blow the carbon out by flooring the pedal and shifting to 2. If there is carbon buildup anywhere in the combustion chamber, the rough ends of the carbon will get red hot and cause the pinging.Īfter three days of driving on the Air Force Base where the speed limit was 35 if you were lucky, the carbon would build up and then act up when you got off the base and tried going up the hill at 50 MPH. If the engine is too hot or the fuel has too low of an octane rating, pre-ignition can cause the pinging. If the timing is too far advanced, the spark itself can cause the pinging. Retarding the timing will cause the engine to cool down a bit and stop the pinging. His engine was running hot and that was causing the pinging. ![]() There was some laziness involved or he didn’t have his timing light at home. ![]() He had done work on the car and reinstalled the distributor without adjusting the timing. He would borrow a wrench so he could retard the timing and stop the pinging that happened every time he stepped on the gas pedal to pass a car or go up a hill. If you worked at a gas station in 1966, you would sometimes see the average mechanic come in with his own car after he was on the highway for a while. Timing that is too far advanced will cause an engine to run hotter. The story gets even longer if we tell some more boring stories. ![]()
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