New Scc Rotary Article
03-20-2003, 12:14 PM
#11
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Originally Posted by vosko' date='Mar 20 2003, 12:17 PM
i just read it last night. i agree it is 2.6L when it is running but when its stopped its 1.3L 
I dont care about the displacement thing anyway. The rotary is still unique compared to the piston engine and he makes a good point that the rotary engine is still in its infancy of development when comparing the <100 Mazda engineers to the thousands of piston engineers over the years....
The article is good, the guy knows his **** about engines in general but he sounds a little cocky like he is the final word on everything....
interesting thoughts about direct injection, wider rotors and intermediate housing too...
03-20-2003, 12:43 PM
#12
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Originally Posted by FCmaniac' date='Mar 20 2003, 10:14 AM
exactly....
I dont care about the displacement thing anyway. The rotary is still unique compared to the piston engine and he makes a good point that the rotary engine is still in its infancy of development when comparing the <100 Mazda engineers to the thousands of piston engineers over the years....
The article is good, the guy knows his **** about engines in general but he sounds a little cocky like he is the final word on everything....
interesting thoughts about direct injection, wider rotors and intermediate housing too...
I dont care about the displacement thing anyway. The rotary is still unique compared to the piston engine and he makes a good point that the rotary engine is still in its infancy of development when comparing the <100 Mazda engineers to the thousands of piston engineers over the years....
The article is good, the guy knows his **** about engines in general but he sounds a little cocky like he is the final word on everything....
interesting thoughts about direct injection, wider rotors and intermediate housing too...
mike
03-20-2003, 04:51 PM
#13
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Originally Posted by j9fd3s' date='Mar 20 2003, 12:23 PM
its all the the way you rate it. a rotary will fire its rated displacement every 360 degrees of output shaft rotation. a piston engine will fire half its rated displacement every 360 degrees of output shaft rotation. so if you take the full piston engine displacement the rotary is twice as large. so its all in how you look at it, if the 13b is 1.3l than a 4.6mustang is 2.3l....
mike
mike
03-20-2003, 05:22 PM
#14
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Originally Posted by j9fd3s' date='Mar 20 2003, 09:23 AM
its all the the way you rate it. a rotary will fire its rated displacement every 360 degrees of output shaft rotation. a piston engine will fire half its rated displacement every 360 degrees of output shaft rotation. so if you take the full piston engine displacement the rotary is twice as large. so its all in how you look at it, if the 13b is 1.3l than a 4.6mustang is 2.3l....
mike
mike
but isn't displacment the volume in a piston engine determined from the top of the pison stroke in the cylinder to the bottom of the cylinder
and the 13B rotary it's when the apex seal on the rotor closes the intake ports just b4 starting what would be called in piston engines the compression "stroke"
i fail to see that the crank shaft and excentric shaft have to do with it
and yes rotarychainsaw the E-shaft is geared to rotate 3 times faster then the rotors
03-20-2003, 05:27 PM
#15
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Originally Posted by RXciting' date='Mar 20 2003, 06:22 PM
and yes rotarychainsaw the E-shaft is geared to rotate 3 times faster then the rotors
It's best not to think about these things I think.
03-20-2003, 05:43 PM
#16
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Originally Posted by RXciting' date='Mar 20 2003, 11:22 PM
[quote name='j9fd3s' date='Mar 20 2003, 09:23 AM'] its all the the way you rate it. a rotary will fire its rated displacement every 360 degrees of output shaft rotation. a piston engine will fire half its rated displacement every 360 degrees of output shaft rotation. so if you take the full piston engine displacement the rotary is twice as large. so its all in how you look at it, if the 13b is 1.3l than a 4.6mustang is 2.3l....
mike
mike
but isn't displacment the volume in a piston engine determined from the top of the pison stroke in the cylinder to the bottom of the cylinder
and the 13B rotary it's when the apex seal on the rotor closes the intake ports just b4 starting what would be called in piston engines the compression "stroke"
i fail to see that the crank shaft and excentric shaft have to do with it
and yes rotarychainsaw the E-shaft is geared to rotate 3 times faster then the rotors [/quote]
i believe it's how much volume the engine displaces in a single crank revolution...
03-20-2003, 05:48 PM
#17
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ok i know this but displacment is calculated in a single cylinder assuming the smart person who made the engine made all the cylinders of the same bore and ****... and then (this i'm not exactly positive about) you have cubic inches which is the total displacment of all the cylinders
03-20-2003, 11:54 PM
#18
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This might help. I copied this from Felix Miata's website, Its has lots of info about rotary engines:
Why does a rotary engine make as much power as a boinger twice its size?
There are lots of reasons, but the main one is that a "2292 cc" piston engine isn't actually twice as big as an 1146 cc 12A Mazda rotary.
That's right! The following comparison of a Pinto engine to the 12A explains why.
A 12A feeds two power cycles into the eccentric shaft for each revolution it makes. Each rotor face displaces a volume of 35.0 cubic inches, which is 573 cc. Therefore, 70.0 cubic inches or 1146 cc's worth of power are delivered to the output shaft for each revolution that shaft makes.
The most common Pinto engine is a 4-cycle, 4 cylinder, having four pistons that each displace 35.0 cubic inches or 573 cc. Exactly two of these four cylinders deliver power to the output shaft in one revolution, which just happens to be exactly the same 70 cubic inch or 1146 cc amount as a 12A is doing in the same amount of time.
A key point here is the element of time. We measure engine size with reference to two things: time, and output shaft movement, revolutions per minute, or RPM. To make some other form of spark ignition internal combustion power plant with distinct intake, compression, power, and exhaust phases as does the 4-cycle piston engine comparable to it, equal parameters have to be given equal consideration. Therefore, since the 12A delivers two power cycles of 35 cubic inches each per output shaft revolution, it is exactly equivalent in this regard to the 4-cycle 4 cylinder Pinto engine that does the same thing.
Another way to look at equivalence is to quit trying to convert the rotary to 4-cycle piston equivalence, instead converting the boingers to rotary equivalence. The number of working chambers or pistons is irrelevant. Simply compare displaced volume converted into combusted mixture per output shaft revolution. The 12A is 35.0 cubic inches times two, or 70.0. The early Pinto just happens to be 35.0 times two as well, making it a 12A equivalent. The 13B is 40.0 times two. Later Pintos just happen to be 40.0 times two as well, making it equivalent to a 13B. An old 2.6 liter six cylinder Datsun 260Z happens to have 26.666 times three, or 80.0 total, same as a 13B. Since 4-cycle boinger pistons only put power to the output shaft every other revolution, they should be rated at half the displacement they claim to have!
There are noteworthy differences. The rotary makes excellent HP because it easily lends itself well to operation at higher shaft speeds (RPM) that get more power pulses into the output shaft. The piston engine delivers it's power in shorter bursts of a nominal 180 degrees of output shaft revolution. The 12A nominally uses 270 degrees to deliver each of it's power "strokes".
A 12A engine is tuned to operate at a higher RPM level than the Pinto, so its maximum HP is higher. However, when both engines are operated at 5000 RPM, the small difference in HP is more a function of each's individual tuning than the differences in basic design. And, it is this correspondence that helps confirm the logic used above to compare the 12A engine to the Pinto 2.3L, and why it is the method of choice in racing classes in which rotaries are permitted to race against boingers and yet be competitive without being dominant. Doing it any differently upsets the competitive balance.
Equivalences other than 2 to 1 used by race santioning bodies are simply an attempt to equalize results instead of using what works for the boingers, capacity for them being the sole primary criteria of equivalence. The use of a factor of 2.6 recognizes that the rotaries operate at higher RPM's than the boingers in the same classes. If we convert the Pinto 2.3L into rotary equivalence, cutting the displacement in half from 140 to 70, the 2.6 becomes 1.3 to get the same equivalence. A maximum operating speed, redline if you will, of 7000 in racing trim for the Pinto, or any 2.3L stock based four for that matter, is probably realistic. Apply the 1.3 factor to the 7000 redline and what do you suppose we find? A 9100 RPM rotary redline in racing trim comparable for that class. Pretty slick of those rule makers, huh? They know more RPM can make more power.
Why does a rotary engine make as much power as a boinger twice its size?
There are lots of reasons, but the main one is that a "2292 cc" piston engine isn't actually twice as big as an 1146 cc 12A Mazda rotary.
That's right! The following comparison of a Pinto engine to the 12A explains why.
A 12A feeds two power cycles into the eccentric shaft for each revolution it makes. Each rotor face displaces a volume of 35.0 cubic inches, which is 573 cc. Therefore, 70.0 cubic inches or 1146 cc's worth of power are delivered to the output shaft for each revolution that shaft makes.
The most common Pinto engine is a 4-cycle, 4 cylinder, having four pistons that each displace 35.0 cubic inches or 573 cc. Exactly two of these four cylinders deliver power to the output shaft in one revolution, which just happens to be exactly the same 70 cubic inch or 1146 cc amount as a 12A is doing in the same amount of time.
A key point here is the element of time. We measure engine size with reference to two things: time, and output shaft movement, revolutions per minute, or RPM. To make some other form of spark ignition internal combustion power plant with distinct intake, compression, power, and exhaust phases as does the 4-cycle piston engine comparable to it, equal parameters have to be given equal consideration. Therefore, since the 12A delivers two power cycles of 35 cubic inches each per output shaft revolution, it is exactly equivalent in this regard to the 4-cycle 4 cylinder Pinto engine that does the same thing.
Another way to look at equivalence is to quit trying to convert the rotary to 4-cycle piston equivalence, instead converting the boingers to rotary equivalence. The number of working chambers or pistons is irrelevant. Simply compare displaced volume converted into combusted mixture per output shaft revolution. The 12A is 35.0 cubic inches times two, or 70.0. The early Pinto just happens to be 35.0 times two as well, making it a 12A equivalent. The 13B is 40.0 times two. Later Pintos just happen to be 40.0 times two as well, making it equivalent to a 13B. An old 2.6 liter six cylinder Datsun 260Z happens to have 26.666 times three, or 80.0 total, same as a 13B. Since 4-cycle boinger pistons only put power to the output shaft every other revolution, they should be rated at half the displacement they claim to have!
There are noteworthy differences. The rotary makes excellent HP because it easily lends itself well to operation at higher shaft speeds (RPM) that get more power pulses into the output shaft. The piston engine delivers it's power in shorter bursts of a nominal 180 degrees of output shaft revolution. The 12A nominally uses 270 degrees to deliver each of it's power "strokes".
A 12A engine is tuned to operate at a higher RPM level than the Pinto, so its maximum HP is higher. However, when both engines are operated at 5000 RPM, the small difference in HP is more a function of each's individual tuning than the differences in basic design. And, it is this correspondence that helps confirm the logic used above to compare the 12A engine to the Pinto 2.3L, and why it is the method of choice in racing classes in which rotaries are permitted to race against boingers and yet be competitive without being dominant. Doing it any differently upsets the competitive balance.
Equivalences other than 2 to 1 used by race santioning bodies are simply an attempt to equalize results instead of using what works for the boingers, capacity for them being the sole primary criteria of equivalence. The use of a factor of 2.6 recognizes that the rotaries operate at higher RPM's than the boingers in the same classes. If we convert the Pinto 2.3L into rotary equivalence, cutting the displacement in half from 140 to 70, the 2.6 becomes 1.3 to get the same equivalence. A maximum operating speed, redline if you will, of 7000 in racing trim for the Pinto, or any 2.3L stock based four for that matter, is probably realistic. Apply the 1.3 factor to the 7000 redline and what do you suppose we find? A 9100 RPM rotary redline in racing trim comparable for that class. Pretty slick of those rule makers, huh? They know more RPM can make more power.
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