Why has the firing order for Chevrolet small blocks changed?

Answer 1

Without getting too heady, it is the same principal as the old 7/4 swap cams. Old firing order 1-8-4-3-6-5-7-2, replaced with 1-8-7-2-6-5-4-3 is attempting to keep the previous cylinders exhaust pulse from interfering with the next cylinders exhaust pulse. What used to happen is that #7 would fire 90 degrees after #5 but pressure from #5's event was still evident in the exhaust system leaving #7 with higher back pressure to contend with and poorer exhaust scavenging as a result. This firing order also keeps the head cooler in theory (I have not seen engineering data that substantiates this) but it makes sense in my head that the power events are more evenly distributed back and forth between the left and right bank. I have also read that this spreads out the work load that the crank has to support by not having 2 events so close on the 5/6, 7/8 crank throws but I am up in the air about this one. I leave that to engineers.