firing order
When switching from 1-8-4-3-6-5-7-2 to 1-8-7-2-6-5-4-3, I think GM was trying to make a smoother running engine. On the old firing order, 5 and 7 are not only right next to each other in order, but also in their physical location in the block and in where they pull intake air from in the plenum.
A lot of pre gen 3 small block guys have tried messing with 4-7 swap cam's, and they have usually found decent results, but at the same time, their firing order is now 1-8-7-3-6-5-4-2, so they wind up with 2 firing next to 4...similar problem as 5-7 in the original firing order. By swapping 4-7 AND 3-2, you get rid of the 5-7 problem and the 4-2 problem. You now have a 1-3 problem though, because the firing order could be looked at as 1-8-7-2-6-5-4-3-1-8-7-2-6-5-4-3...on and on...but 1 and 3 are closer to the throttle body than 5 and 7 are, so maybe GM saw fit to move the problem area closer to the throttle body to help wave propagation through the intake plenum...2 and 4 are not quite as close to the TB as 1 and 3 are...I dunno.
A lot of pre gen 3 small block guys have tried messing with 4-7 swap cam's, and they have usually found decent results, but at the same time, their firing order is now 1-8-7-3-6-5-4-2, so they wind up with 2 firing next to 4...similar problem as 5-7 in the original firing order. By swapping 4-7 AND 3-2, you get rid of the 5-7 problem and the 4-2 problem. You now have a 1-3 problem though, because the firing order could be looked at as 1-8-7-2-6-5-4-3-1-8-7-2-6-5-4-3...on and on...but 1 and 3 are closer to the throttle body than 5 and 7 are, so maybe GM saw fit to move the problem area closer to the throttle body to help wave propagation through the intake plenum...2 and 4 are not quite as close to the TB as 1 and 3 are...I dunno.
Every engine has a firing order, it won't turn without it. The reason for the firing order change was to smooth out the idle. This firing order is what is on the Fords and Chryslers (IIRC). The old firing order was a bit of an odd firing order. This also affects the exhaust sound of the engine, the reason why the LT1 and LS1 do not sound the same.
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