11/28/2023 0 Comments Retarding ignition timing![]() This shows that an increase in header temperature of 100 deg C = 2000 RPM shift in power-band. ![]() The pipe will actually be tuned to 11930 at the higher temperature. Assuming the pipe is tuned to 10000 RPM, and we have some way to increase the temperature in the exaust header by 100 degrees, using the relation:Ĭrank-angular-displacement = (0.012 * tuned-length * RPM) / speed-of-sound. So back to the original idea!! Speed of sound is faster in hotter gasses. This means the speed of sound changes proportionaly to the square root of the change in temperature.Īssuming average temp of exhaust gases is 400 deg C (average of 800 deg C at cylinder, and 150 deg C at silencer exit) - the seed of sound in the pipe is an average 518 m/s. With regards to temperature affecting pipe timing:Ĭ (speed of sound) = sqrt(1.4*pressure/density) In an interesting turn about - I have looked up some info from a reliable source, and found that a lot of information out there is at least confusing, or just plain wrong. Jon (the new service guy) using Micah's computer.Īctually, if you look at the ignition map, the earliest sparc firing occurs at 3500 RPM, the sparc then fires later and later until 12000 RPM when it is only 7 degrees before top dead centre. The combustion is basically trying to push the piston backwards, creating lots of heat. This is because the combustion is occuring too soon as the piston is rising. If your ignition is too advanced, you will blow holes in pistons and melt sparkplugs. Granted it isn't a constant combustion rate, but it is far more constant than the piston speed. As the RPM increases the piston travels faster, so the charge has to fire earlier so as to give the best combustion at the correct piston position. The reason ignitions advance as the RPM increases is because given a constant combustion rate, the combustion is timed to give the best push on the piston. The more advanced the ignition is, the more degrees before TDC the ignition fires. Seems like some people are saying "retarding" for when the igintion fires earlier, aka before TDC.Īdvancing the ignition is making it fire more degrees before TDC. I think the confusion here is the terms "retarding" and "advancing". This is all dependent on just how much you do increase compression. If you wished to use high octane, leaded racing fuel, you would theorhetically need to lower head volume, change the head profile, and probably increase advance across the range while also holding on to it a bit longer. Suzuki's stock ignition curves are designed to be able to be used with very low octane gas and to ensure the bikes are relatively bulletproof. I have found amazing differences on our bikes with head combinations, ignition maps and static advance. It is main a matter of the fuel you are using, head volume, deck height and head profile. It starts to become less after this point and how much and where makes a BIG difference in the power the engine makes. 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 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. Retarding the timing will indeed reduce power output (based on an optimised stock bike) all other things being equal.
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