I see that Miker mentions Hedmans Tri Y firing order specific headers. I am puzzled as to the construction of such a device and looked up pictures of these items.

How do these tri y  qualify as "firing order specific".
A true F.O.S. design incorporates the tubes from each side to scavenge the gasses as each cylinder fires in its order taking advantage of pulse theory.

F.O.S. headers usually have a pretty curious appearance and generally wont fit into a conventional automotive frame.
So how do these headers qualify under a firing order specific label?
Oldmics

Ideally, they pair cylinders that are 180 degrees apart.  That's not usually possible without tubes crossing over, increasing expense, so instead they get as close as possible, keeping it as simple as possible.  On a Y, they will be paired 1 + 3, 2 + 4, 5 + 6, 7 + 8.
I think the idea is to keep the flow path as unobstructed as possible.  Lots of info about it if you google it.



Lawrenceville, GA

You’ll have to remember that the Ford Y does have a unique firing order so any firing order specific Tri-Y headers that work with an opposing firing order will not be correct for a Ford Y.  I did run a set of 4-2-1 (Tri-Y) headers on the 2016 Engine Masters Challenge engine over my 4-1 headers and they were worth a few extra points.  The peak horsepower was the same with both sets of headers if collector sizing had remained the same but the 4-2-1 headers brought the torque numbers in earlier which helped the overall points score at the EMC competition.  While the header tubes were paired so that they would be firing order specific for the EMC, tests were made with the tubes intentionally switched so that they would be the complete opposite of being firing order specific.  In these instances, the headers fell down in performance so the pairing idea works for this particular set of headers.
 
Since the EMC competition, I have tested a set of unequal length tubes (by design) 4-1 headers with merge collectors on the same engine and those headers also produced a score better than the 4-2-1 headers.  The unequal length design idea came from Jerry Jardine and makes sense once it’s realized what the exhaust pulses are doing when the reach the collector.  The unequal tube lengths on those headers are designed to equalize the exhaust pulses at the collector and minimize the effect of cylinders 2 and 8 inhibiting the flow of cylinders 1 and 6 at the collectors.  Short of making the header tubes cross under the engine so that a true 180° design can be capitalized upon, the unequal length headers is an attempt to even out the exhaust pulses at the collectors.
 
But at this same header test, Joe Craine had brought down his 4-1 FPA headers for a ’55-57 Thunderbird and with some additional collector extension added to them these ran better than anything else that’s been tried thus far.  So at this point we’ve tried some ‘No Science’ chassis headers that simply work better than all the other headers.  This is twice now that the FPA headers have been tested on different engines and in both cases those headers prove to make as much if not more power than headers that have some serious thought put into them.

Lorena, Texas (South of Waco)

Here’s the link to some of the header testing performed on the 322” dyno mule.  In this test, the FPA headers technically came out on top.
http://forums.y-blocksforever.com/FindPost99070.aspx

Lorena, Texas (South of Waco)

The FPA headers are a stepped design, unlike most 4-1 headers.  It would be interesting to know if their headers for other engines tend to work just as well or if the T-Bird headers are just a fluke.


Lawrenceville, GA

So the bottom line is that the tri Y units are not true 180* F.O.S. devices.
Oldmics

Oldmics, I used the term loosely, or incorrectly. The Hedmans had one side different from the other side, where the Red's triy's looked the same. A couple local shops "converted" 4-1 headers to triy's up here for years. Mid range torque was the goal, and they seemed to work. They didn't show improvement on the strip, but made a nice street setup. We got to using the term loosely, and it's come back to haunt me.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

I had a set of headers on my 428 Pontiac Firebird back in the 80's. They had a very long collector box and the length of the tubes was equalized in the box. Made an easy fit at the head with a normal appearing 4-1. I recall they had a very weird sort of pinging sound to them at idle. I assume from the equal length tubes in the box. Ran like the wind in that setup.

Y's guys rule!
Looking for McCullouch VS57 brackets and parts. Also looking for 28 Chrysler series 72 parts. And early Hemi parts.

MoonShadow, 292 w/McCulloch, 28 Chrysler Roadster, 354 Hemi)
Manchester, New Hampshire

Miker
Please dont think that I was bashing your terminology in referring to your exhaust.
Those Hedmans appear to be marketed as F.O.S. devices along with a few other companys doing the same marketing ploy.
It would be easy to fall into there sales .
I just wanted to understand why they were referred as such. Thanks to this group I now understand.

Oldmics    (older and now just a little bit wiser)

Most Tri-Y’s and/or 4-2-1 headers are not a true 180° design but when done as being ‘Firing Order Specific’ do separate the tubes such that the cylinders that fires first in a pair on a given bank are not paired together at the tubes.  This does minimize the effect of the exhaust pulses getting bunched up before the collector and does aid to some degree for a better scavenging signal.  Four tube headers (4-1) are obviously not firing order specific.
 
The inherit flaw to most V8 engine designs is that there are two cylinders on each bank that fire consecutively.  On the Ford Y, this would be cylinders 2 & 1 on the right bank and cylinders 8 & 6 on the left bank.  The cylinder that fires first on a same side paring is not fully evacuated from the collector when the second cylinder in that pairing fires.  This tends to load up the collector which in turn prevents a clean evacuation or scavenging of those cylinders.  Ideally you would like to see a sequential or even pulsing at the collector.  This would be your 180° design.  Tri-Y headers or altering the lengths of the tubes is simply a way to help this along without getting stupid with some of the header tubes running over or under the engine.
 
The optimal way to have a true 180° design for a V8 with a conventional crankshaft would be to cross the appropriate header tubes from one side of the engine to the other.  Doing this and keeping the header tubes both equal in length and at the optimal length would be the challenge.  For the Ford Y, this would involve taking two header tubes for each bank and having them exit in the collector on the opposite bank; in this manner the collectors could evacuate fully by alternating from side to side in an equal fashion.  That would be a bunch of tubes snaking around.  The Ford GT40 cars for the Lemans races did this by crossing the tubes across the top of the engine.  Most car chassis do not have the room under the car to start moving header tubes from one side to the other.  But there are exceptions; I do have sets of FE headers for a 63-64 Galaxy and a 69-70 Mustang that do have the crossovers under the engine.  These two sets of headers are a true 180° design.  Early on I had a set of 180° tube headers for a 1964 Thunderbolt (427 HiRiser) and these also incorporated the crossover tubes under the engine.
 
Here’s a picture of some 180° headers which explains why you don’t see them very often.
 

Lorena, Texas (South of Waco)