Based on some resources, I was able generate a list of all theoretical firing orders for an LS engine with a cross-plane crankshaft. Here they are (
R denote which bank each cylinder in the firing order belongs to):
1-5-4-2-6-8-7-3 LLRRRRLL 1-5-4-3-6-8-7-2 LLRLRRLR 1-5-7-2-6-8-4-3 LLLRRRRL 1-5-7-3-6-8-4-2 LLLLRRRR 1-8-4-2-6-5-7-3 LRRRRLLL 1-8-4-3-6-5-7-2 LRRLRLLR 1-8-7-2-6-5-4-3 LRLRRLRL 1-8-7-3-6-5-4-2 LRLLRLRR
The standard LS firing order is
1-8-7-2-6-5-4-3, which does a decent job of alternating firing between banks as much as possible.
A popular modification that recently came to my attention is known as the "4/7 swap", which switches the firing order of cylinders 4 and 7. What's interesting to note here is that it causes all 4 cylinders on one bank to fire in succession, followed by the other bank's 4.
I would have imagined that this firing order should be avoided because it places more load on the crankshaft and rod bearings when all of the cylinders on one bank are fired one after another.
So is there any benefit to be reaped from performing this modification?
Some forums appear to indicate a minor improvement in power/torque output, but I fail to see how this would be the case.
Here is the cylinder numbering convention on an LS engine. All cylinders on Bank 1 (
L) are odd, Bank 2 (
R) are even: