OK, so here's the specs for two variants, the (sane) "single length 2-step tri-y" and the (questionable) "double length 3-step tri-y".
--- Megaphone Collector Specs ---( Diffuser or Diverging Cone Shape )---
*** Note: this will common to both designs, and matches the "Best HP/TQ Tuned Collector Length" from the mid-range calculations at realistic EGT. To save space, the last 4"-6" would be flex tube with an interlock liner.
Diameter= 1.5 taper to 2.5 Length= 16 inches
--- 2-Step "Single length" TRI-Y Pipe Specs ---
1st Y-Segment 1st Step Dia. inches= 1.375 Length= 13.5
2nd Y-Segment 3rd Step Dia. inches= 1.625 Length= 13.5
Combined Total of all Segment Lengths = 27 inches long
Including megaphone and 2" for cat. flange, -3" for exhaust runners inside the head = 42"
--- 3-Step "Double length" TRI-Y Pipe Specs ---
1st Y-Segment 1st Step Dia. inches= 1.375 Length= 27
1st Y-Segment 2nd Step Dia. inches= 1.5 Length= 13.5
2nd Y-Segment 3rd Step Dia. inches= 1.625 Length= 13.5
Combined Total of all Segment Lengths = 54 inches long
Including megaphone and 2" for cat. flange, -3" for exhaust runners inside the head = 69"
And how, might you ask, do you fit all that between the radiator and the engine? Here's one way
:
(Note: Y merges are marked / tied together with the green tape. The 'pipe' is 15mm plastic-foam "gap filler" as used for sealing building cracks, in case you were wondering - actual diameter more like 16mm)
Madness? ... THIS! IS! SPARTAAAAAA!
But more seriously, using the aforementioned ram horn header as an "as far as you can push it" scenario:
* The ram horn header has all the ports taking a sharp turn (looks like 1D) straight out of the port, while this only has a 1.5D turns starting 4" from the port.
* Cylinders 2 and 3 have a similar amount of total bend at a similar radius to the ram horn header.
* Cylinders 3 and 4 have a bit more total bend than the ram horn, but can use much more 'swoopy' curves.
So, another question comes to mind... can a ram horn header only get away with this much bend because the 'ram horn' itself is a constant, steady turn? Or is having straight sections between the bends a
good thing? In either case, next thing I'll try is a more traditional rams horn with primary Y merges just below the flange, and extra length from swoopyness below - but that's for another day.
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EDIT:
And I just realised I put the primary merges at 27" from the exhaust valve, rather than 40.5" - whoops! Just imagine them paralleling thier respective partners a little further before merging. And that the lower section might be better if it spiralled (like the Mazda header) rather than taking an S-bend. That's what comes of doing modelling after midnight I suppose
...