Here is our engine information from myfordfocus.com which proves our firing order is 1-3-4-2
Firing order is continuous
So it looks something like this... 1-3-4-2-1-3-4-2-1-3-4-2...etc.
Look at that pattern, you can see how other number eventually pair up (1-3, 3-4, 4-2, 2-1)
BUT never does the 1-4(4-1) pair or 3-2(2-3) appear. (I didn't get this at first glance)
Now that we know how firing order runs, it's time to answer the question-
How to pair them on the header?
Here is my though process-
If the firing order is 1-3-4-2
You pair 1 and 3 then you pair 4 and 2
Exhaust enters both 1 and 3 and collects together at the same time (creating downforce to push the exhaust out faster, which is what we want)
And the same for the 4-2 pair
According to my thinking when your exhaust collects it goes faster because you have the force of two releases simultaneously so that while one is reaching the collector pipe, 3 is released giving it an extra push so on and so forth.
This was found in my research-
If cylinder #1 is paired with #2, then #3 and #4 are paired.
If cylinder #1 is paired with #3, then #2 and #4 are paired.
However, both these set ups are considered sequential pairing because each secondary gets 2 back to back pulses. Therefore, these set ups are the same and can be considered as 1 configuration.
Next we pair #1 with #4, and then #2 and #3 are paired. This is considered non-sequential pairing, since the pulses alternate from one secondary to the other. We canít pair #1 with anything else so the fact of the matter becomes there are only 2 ways to configure a 4-cylinder.
If I am correct then you want to be looking for a header that pairs the same as the firing order. On top of that if this is a correct assumption, then the Escort GT header is the wrong firing order.
How do I know this?
Well if you look at the table in the first picture, the Zetec engine has the same firing order
So from there I looked up some zetec headers.... And to add to my confusion I found that they had two configurations for the 4-2-1 design. Focus Sport uses the concept I believe in, pairing up 1-3 and 4-2, but I found zetec headers on myfordfocus.com and steedafocus.com that use 1-4 2-3 for pairing. So I decided to look into the zetec Shorty header- JBA uses 1-3 and 4-2 pairing.
The majority of zetec headers, and also the more known and loved brand names use the 1-3 and 4-2 pairing concept, yet the SVT Focus pairing is 1-4 and 2-3 as well as the 86-90 Escort GT header that we know works. And Ford knows these engines better than us, so after all this I was wrong and you want to actually find a header where the first and last ports are paired and the two middle ones are paired.
It seems there is more research that shows I was probly wrong in my assumptions and that the following design is RIGHT (pairing the first and last together)
I am just going to state that this is all based purely on my thought out logic. I do not know the facts of how firing order works and what the best route for exhaust flow is. I appologize if I slandered any brands, even though I feel I did not because the two websites that used the non-sequential firing order do in fact carry the sequential firing order headers as well. It may also be a misrepresentation from stock photography. So my appologies.
Useful information that counters my conclusion, seems his reasearch is more sturctured and backed, so we will go with his advice.
Originally posted by 02ztsian
OK I read and re-read this post a couple of times and have a few thoughts about pairing cylinders.
First, let's do some determination of where each cylinder is in the 4-stroke cycle in relation to the other cylinders.
If the firing order is 1-3-4-2, we can assume the following:
1 3 4 2
P _ _ _
_ P _ _
_ _ P _
_ _ _ P
And the blank spaces are representing the remaining cycles of the 4-stroke cycle.
So, with the 4-strokes being Intake Compression Power Exhaust in this order we can fill in the blanks as follows:
1 3 4 2
P E I C
C P E I
I C P E
E I C P
We read bottom to top for each individual cylinder's 4 stroke cycle.
Everyone follow? OK sorry for the Auto Shop 101 but I want to make this as clear as possible.
OK so we ask ourselves what are the best cylinders to pair up? We have seen the 1-3 and 2-4 pairings as well as the 1-4 and 2-3 pairings. So what is happening to the pairs mate as each cylinder is on the exhaust stroke?
Well lets look at the chart-in a 1-3 and 2-4 pairing we see:
when 1 is on the Exhaust the 3 is on the Intake.
when 3 is on the Exhaust the 1 is on the Power.
when 4 is on the Exhaust the 2 is on the Intake.
when 2 is on the exhaust the 4 is on the Power.
Conversely, in the 1-4 and 2-3 pairings, we find the following:
when 1 is on the Exhaust the 4 is on the Compression.
when 3 is on the Exhaust the 2 is on the Compression.
when 4 is on the Exhaust the 1 is on the Compression.
when 2 is on the exhaust the 3 is on the Compression.
Very interesting. Notice that they all are the same (180* apart) as opposed to alternating.
What I am attempting to show here is the natural pairings of 1-4 and 2-3 due to having each partner 180* apart on each revolution of the crankshaft. As each exhaust cycle starts, the partners cycle, the Compression, has had the exhaust valve closed for the cycle previous (Intake) and the cycle following (Power) thus eliminating any chance for reversion (the crossing over of exhaust gases being drawn in to the fresh intake charge) or having both exhaust valves open at the same time. This can happen as, in the case of 1-3 and 2-4 partnerships, as one exhaust valve starts to close the partners starts to open at the end of the power cycle.
What does this all mean: well, from the S&S Header website-quote:"The optimum situation is the four cylinder because of it's firing cycle. Every 180 degree of crankshaft rotation there is one exhaust pulse entering the collector. This is ideal timing because, as one pulse exits the collector, the next exhaust valve is opening and the vacuum created in the system pulls the exhaust from the cylinder. In this ideal 180 degree cycling the collector outlet diameter only needs to be 20% larger than the primary tube diameter. "
So, having the exhaust cycles firing 180 degrees apart would be the ideal situation.
And that, my children, is why I feel say the perfect exhaust pairing for the Ford 1-3-4-2 firing order is 1-4 and 2-3 matched as pairs in a 4-2-1 header.