V12 Cylinder Numbering & Firing Orders
Could one of the engine experts clarify what the cylinder numbering scheme is on the later V12's, such as the 550 / 575 / 599?
When you're at the rear of the motor, facing the flywheel, are cylinders 1-6 on the right, 7-12 on the left, and cylinders 1 & 7 are at the front of the motor, with 6 & 12 at the flywheel end?
Or are cylinders 1 & 12 at the front, and 6 & 7 are at the firewall?
On the firing order question, I understand Ferrari changed the firing order of the V12 during the transition from the 456 to the 456M.
The "old" firing order was 1-12-5-8-3-10-6-7-2-11-4-9, but it's not clear to me under which cylinder numbering scheme this is.
The "new" firing order is 1-7-5-11-3-9-6-12-2-8-4-10, but again it's not clear under which cylinder numbering scheme.
What I find interesting, is that both firing orders are exactly the same, if the cylinder numbering scheme is changed from 7 being at the front, and 12 is at the rear, to where 12 is at the front, and 7 is at the rear.
Going through the 456, 456M, and 575M workshop manuals, all the cam timing adjustments are done on cylinders 1 and 12. This leads me to believe they are all numbered with the front cylinders as 1 and 12. The Enzo and 599 both have the same firing order as the 456, 575M, and 612. The firing order on all the 65 deg V12s, except the 456M, is 1-12-5-8-3-10-6-7-2-11-4-9.
Note these are 65 deg V12s vs the 60 deg V12s of the earlier cars, if that has any bearing. Maybe Brian can chime in. Brian has stated he thinks the reason they changed the order on the 456M was cross-firing of the spark plug wires. On the 575M and later cars with coil on plug ignition, cross firing is not an issue because there is no primary current passing through the wires to the coils, just coil charging current.
On the 550, though, the same three coil pack for each cylinder bank was used as on the 456 5.2 and the 456M, so why a different firing order? No reason why the 5.2 456 should have had a bigger cross-fire problem than the 550 that I can see, unless they better separated or insulated the 550 spark plug wires. Nope, just checked. The 456, 456M, and 550 all use exactly the same spark plug harness.
Beats me. Looks like an experiment that failed, like a few other things I could name. 5 valves, rubber timing belts, eccentric suspension adjustment, etc.
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