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      11-03-2012, 05:39 PM   #7
N0OS3's Avatar

Drives: E90
Join Date: Feb 2010
Location: Oak Harbor, WA

iTrader: (5)

It was explained to me, one of the major differences in Inline 6 vs V configuration six is the firing timing... this is how it's explained in a V8:

With a V8, a cylinder fires every 90 degrees of crankshaft rotation, so that part is even firing. But the crankshaft only has 4 throws, not 8 throws, so you don’t have complete freedom to choose firing order. What you find if you scratch your head and think about it for a while is that on each bank, the firing sequence will be two intervals of 180 degrees of crank rotation between firing, one of 90 degrees, and one of 270 degrees. So the cylinder firing on each bank is not evenly spaced. The crossover pipe allows the exhaust system to partially compensate for that. When you get to the point that the 90 degree interval is firing on one bank, that’s also about the point where the 270 degree interval is occurring on the other bank, so the crossover pipe lets a bit of exhaust from the side that is firing on 90 degree interval at that instant cross over to the side that is on 270 degree interval at that instant.
Layman's terms:
Considering the whole engine, the 8 cylinders fire evenly, meaning bang, bang, bang, 8 times, evenly spaced, in a row. But if you just consider the 4 cylinders on the left bank of the V, or the 4 cylinders on the right bank, neither bank fires evenly. Each bank of 4 goes bang, pause, bang, bang, pause, bang, extra long pause, and repeat. Furthermore, it works out such that the short interval “bang, bang” on one side corresponds in time to the extra long pause on the other, so the crossover pipe lets some of the momentarily higher flow of exhaust from the short interval “bang, bang” cross over to the other side where there is momentarily lower flow because of that bank’s long pause. The earlier post tried to explain a bit more about why that is, namely degrees of crankshaft rotation between firing pulses related to a 4 throw, V8 crankshaft, but it sounds like it failed to do that clearly enough.
So, a V6 would be firing at approximately 120 degrees on each side... an inline six fires at 60 degrees because they're in a straight row (so i'm told)... that being said, it's a lot easier to work with the exhaust for compensating scavenging loss... [he says you work with backpressure more than you do anything else]

Anyone can correct me (or my exhaust guy that explained this to me) if i'm wrong...

Last edited by N0OS3; 11-03-2012 at 08:43 PM.