2014 yz450f - Using maps



2 replies to this topic
  • YzCas

Posted September 16, 2014 - 09:09 AM

#1

What is the rule of thumb when using the gytr tuner if you add fuel do you add timing when do you know you need more timing?

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  • grayracer513

Posted September 17, 2014 - 09:15 AM

#2

There is no rule of thumb.  Ignition timing is not significantly affected by the air/fuel ratio, nor are the two adjustments really linked in any way. 

 

Adding or subtracting fuel from a map is adjusting the air/fuel ratio by increasing or decreasing the fuel injector output slightly.  Each plus or minus one is about equivalent to one number larger or smaller main jet, perhaps even less.  So, when going from 0 to +4, it's something like going from a 165 to a 170.  The reference isn't quite that cut and dried because the actual fuel metering at any setting is in part determined by info from the barometric pressure sensor in the system at startup.  More isn't always better.

 

Ignition timing is dependent on the speed of the engine, the amount of load it's under, and the burn rate of the fuel, which is nearly constant in any case.  The basic technical problem is simply that the piston is a moving target, and ignition has to take place before it gets over TDC in order for the pressure from the expanding gasses to bear down on it effectively.  The most mechanically effective range of rod/crank angle takes place starting at around 20-30 degrees after TDC.  If the combustion pressures rise to a high enough level to push the piston down the bore at this point, it will produce more power than if it happens later, but at 8000 RPM, for example, it takes only 7.5 milliseconds for the crank to rotate 360 degrees.  The fuel will burn to a point of high, effective cylinder pressure in about 1 millisecond, variably, during which time the crank would move about 50 degrees.  So if you want it up to pressure at somewhere near 25 after top, you have to light it at somewhere near 30 before top to accomplish that.

 

Retarding the timing just a little from optimum will make the pressure peak happen later, with less effect, and reduce power.  Advancing it beyond optimum makes the pressure peak too early, which means that it will bear on the piston without being able to drive it through the most mechanically advantageous part of the stroke, falling off before that range is run all the way through.  It can also raise cylinder pressures to the point that it causes some part of the burning fuel to simultaneously detonate, and in severe cases, that is as good for the engine as shooting at the top of the piston with a gun.

 

Altitude is one of the primary influences on timing because increasing altitude decreases the air density, which decreases dynamic compression, which slows the fuel burn a little bit.  Most stock maps will respond favorably to adding timing in small increments across the board because they are mapped somewhat conservatively in the interest of reliability.  The factory also retards timing in certain ranges to take some of the snap out so as to increase rideability.  Whether or not more timing helps or hurts your particular application depends on way too many things for there to be any certain rule to go by.  Just have to experiment.



  • YzCas

Posted September 17, 2014 - 10:52 AM

#3

There is no rule of thumb. Ignition timing is not significantly affected by the air/fuel ratio, nor are the two adjustments really linked in any way.

Adding or subtracting fuel from a map is adjusting the air/fuel ratio by increasing or decreasing the fuel injector output slightly. Each plus or minus one is about equivalent to one number larger or smaller main jet, perhaps even less. So, when going from 0 to +4, it's something like going from a 165 to a 170. The reference isn't quite that cut and dried because the actual fuel metering at any setting is in part determined by info from the barometric pressure sensor in the system at startup. More isn't always better.

Ignition timing is dependent on the speed of the engine, the amount of load it's under, and the burn rate of the fuel, which is nearly constant in any case. The basic technical problem is simply that the piston is a moving target, and ignition has to take place before it gets over TDC in order for the pressure from the expanding gasses to bear down on it effectively. The most mechanically effective range of rod/crank angle takes place starting at around 20-30 degrees after TDC. If the combustion pressures rise to a high enough level to push the piston down the bore at this point, it will produce more power than if it happens later, but at 8000 RPM, for example, it takes only 7.5 milliseconds for the crank to rotate 360 degrees. The fuel will burn to a point of high, effective cylinder pressure in about 1 millisecond, variably, during which time the crank would move about 50 degrees. So if you want it up to pressure at somewhere near 25 after top, you have to light it at somewhere near 30 before top to accomplish that.

Retarding the timing just a little from optimum will make the pressure peak happen later, with less effect, and reduce power. Advancing it beyond optimum makes the pressure peak too early, which means that it will bear on the piston without being able to drive it through the most mechanically advantageous part of the stroke, falling off before that range is run all the way through. It can also raise cylinder pressures to the point that it causes some part of the burning fuel to simultaneously detonate, and in severe cases, that is as good for the engine as shooting at the top of the piston with a gun.

Altitude is one of the primary influences on timing because increasing altitude decreases the air density, which decreases dynamic compression, which slows the fuel burn a little bit. Most stock maps will respond favorably to adding timing in small increments across the board because they are mapped somewhat conservatively in the interest of reliability. The factory also retards timing in certain ranges to take some of the snap out so as to increase rideability. Whether or not more timing helps or hurts your particular application depends on way too many things for there to be any certain rule to go by. Just have to experiment.

. Thank you for that explanation it's highly appreciated.





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