Wiseacre Dave
Well-Known Member
Greetings clever viewers!
I've received a very nice 1835 cc motor from Scott Cassler, and I'm trying to learn more about how it works. I've studied the threads here, including this one: https://www.homebuiltairplanes.com/...et-this-great-plains-vw-to-start.19703/page-2
I understand how the firing order works for the motor with the Slick magneto and electronic ignition (both of which I have). I understand that the cylinder numbering is arbitrary as long as the magneto knows which cylinder is on the combustion stroke, but I'm confused about something. Why in the stock auto VW does the firing alternate between sides of the motor (1st cyl on 1 side, then 2 cylinders fire on the other side, and then back to the orginal side for the last cylinder), whereas in the aircraft application both cylinders on one side are fired and then the two on the other side are fired? Doesn't the crankshaft/camshift determine the progression of firing between the case sides? I presume it's a matter of balancing/vibration and that it is possible to achieve that with different firing orders.
I suspect I'm missing something critical.
Update: I think I found the answer to my question by studying my own drawing! The stock VW firing order (4 1 2 3) is just a permutation of the firing order based on my cylinder numbering for the aircraft firing order (1 2 3 4). In other words, the cylinders ARE fired in the same relative order for both numbering systems. It's like cutting a deck of cards: after the cut the cards still have the same relative order with respect to each other; but they occur in a different counting order. Conclusion: the two firing orders really are the same but a different cylinder is fired first in each ordering. Ain't math great!
I've received a very nice 1835 cc motor from Scott Cassler, and I'm trying to learn more about how it works. I've studied the threads here, including this one: https://www.homebuiltairplanes.com/...et-this-great-plains-vw-to-start.19703/page-2
I understand how the firing order works for the motor with the Slick magneto and electronic ignition (both of which I have). I understand that the cylinder numbering is arbitrary as long as the magneto knows which cylinder is on the combustion stroke, but I'm confused about something. Why in the stock auto VW does the firing alternate between sides of the motor (1st cyl on 1 side, then 2 cylinders fire on the other side, and then back to the orginal side for the last cylinder), whereas in the aircraft application both cylinders on one side are fired and then the two on the other side are fired? Doesn't the crankshaft/camshift determine the progression of firing between the case sides? I presume it's a matter of balancing/vibration and that it is possible to achieve that with different firing orders.
I suspect I'm missing something critical.
Update: I think I found the answer to my question by studying my own drawing! The stock VW firing order (4 1 2 3) is just a permutation of the firing order based on my cylinder numbering for the aircraft firing order (1 2 3 4). In other words, the cylinders ARE fired in the same relative order for both numbering systems. It's like cutting a deck of cards: after the cut the cards still have the same relative order with respect to each other; but they occur in a different counting order. Conclusion: the two firing orders really are the same but a different cylinder is fired first in each ordering. Ain't math great!
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