Inliners International Forums General Discussion Hi Performance GMC/Old Chevy Single Headre Design Questions.

Look at your firing order and the port arrangement. Note that the siamese (2/3, 4/5) exhaust ports are separated by one other firing (1 & 6). This means that 3 & 4 would have to be open over 240 degrees before overlapping 5 & 2. You are thinking in terms of them flowing at the same time, they are not, it is one and then the other. When 1, 2 and 3 enter the collector, they are equally spaced 120 degrees apart same with 4, 5 and 6. Add them all together and they all flow, one after the other, into the exhaust. 4 into one makes more power because of this.