Not quite....cj wrote: The best scavenging is done when the cylinders paired are 180 degrees opposite each other in the firing order, not next to each other. That is why pairing 1 & 4 and 2 & 3 is the ideal, not 1 & 3 and 2 & 4. Another area of power loss with a header can come from a poorly designed collecter.
Cylinders 1 & 3 ARE 180 degrees apart. As are 2 & 4.
Go to TDC on No.1 and then turn your front pulley 180 and No.3 WILL be at TDC.
This is a FOUR Stroke engine remember so the crank turns 720 degrees for all cylinders to fire.
The extractor shown in the pic is the ideal design for an everyday car. IE: Better low and midrange torque and a MILD increase in horsepower.
No.1 fires and then sucks No3 along with it, No4 fires and sucks No2 along so your pulses at the tailpipe come out 1,3,4 & 2 same as the firing order.
1 & 3 on the first rev and then 4 & 2 on the second revolution, ALL 180 degrees apart.