This chart shows the piston position set against crank degrees around TDC.
I have the complete 720 degrees but I'll have to find it...
The far right two columns are the piston position in inches and the increment of piston movement per degree. Notice the degree of increment change around 17-18-19 ATDC. See how the piston is really moving? I can see a typo in that column but for the most part the increment doubling is the speed doubling. It has to accelerate to do this and the degrees before 18 ATDC show the dwell at TDC, and the slowness of the incremental changes and then the actual implicaton of the acceleration.
Remember we wanted to know the point of peak cylinder pressure? At some point before we see the piston at 18 ATDC the peak cylinder pressue occurs.
I had brought up the idea of the shape of the individual cylinder power pulse in relation to the 7M. The power pulses regular occurence in relation to each other produce another esoteric spec:
That the peak cylinder pressure is representative of peak torque as compared to mean torque.
Simply put but hard to understand- the spec of our stock torque is a representation of only one tenth the torque the engine produces at peak cylinder pressure. That makes it routine for us to figure out the momentary torque per degree exerted on the reciprocating parts.
Here is where the stock ignition settings matter. Toyota figured out that at idle the torque necessary to achieve idle and everything in between. An example of this is that in a properly tuned engine one could advance timing to the point of stalling the engine. What is really happening here now that we know we are messing with the unchangeable crank and rod geometry?
Another chart shows the relationship of the piston position to piston speed at the crank degrees.
From these studies the understanding of the piston's effect on the captured intake charge can be made. Once the intake charge is being compressed there is another study that allows the understanding of the rate temerature and pressure climbs as it approaches TDC.
The knowledge of the charge temperature and pressure is on what the Toyota designers based our ignitions.
I have the complete 720 degrees but I'll have to find it...
The far right two columns are the piston position in inches and the increment of piston movement per degree. Notice the degree of increment change around 17-18-19 ATDC. See how the piston is really moving? I can see a typo in that column but for the most part the increment doubling is the speed doubling. It has to accelerate to do this and the degrees before 18 ATDC show the dwell at TDC, and the slowness of the incremental changes and then the actual implicaton of the acceleration.
Remember we wanted to know the point of peak cylinder pressure? At some point before we see the piston at 18 ATDC the peak cylinder pressue occurs.
I had brought up the idea of the shape of the individual cylinder power pulse in relation to the 7M. The power pulses regular occurence in relation to each other produce another esoteric spec:
That the peak cylinder pressure is representative of peak torque as compared to mean torque.
Simply put but hard to understand- the spec of our stock torque is a representation of only one tenth the torque the engine produces at peak cylinder pressure. That makes it routine for us to figure out the momentary torque per degree exerted on the reciprocating parts.
Here is where the stock ignition settings matter. Toyota figured out that at idle the torque necessary to achieve idle and everything in between. An example of this is that in a properly tuned engine one could advance timing to the point of stalling the engine. What is really happening here now that we know we are messing with the unchangeable crank and rod geometry?
Another chart shows the relationship of the piston position to piston speed at the crank degrees.
From these studies the understanding of the piston's effect on the captured intake charge can be made. Once the intake charge is being compressed there is another study that allows the understanding of the rate temerature and pressure climbs as it approaches TDC.
The knowledge of the charge temperature and pressure is on what the Toyota designers based our ignitions.
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