well i started this venture on several reasons. first i have a DOHC ZC and i bought a OEM cast upper ZC exhaust mannifold, it didn't come with the lower downpipe. some ppl said get the z6 others said to use the y8.

i've been hacking OEM collectors to remove the restriction of flow.

https://honda-tech.com/forums/honda-crx-ef-civic-1988-1991-3/my-moose-mod-d16y8-header-2729725/

so here we start here's some specs:

D16z6 downpipe - info - D16y8

43mm(1.69") - flange I.D. - 43mm(1.69")
50mm(1.97") - secondary pipes O.D - 49mm(1.93")
49mm(1.93") - bend choke point - 45mm(1.77")
437.8mm(17") - lenght of secondary pipe - 304.8mm(12")
88.9mm(3.5") - lenghten of V merger - 88.9mm(3.5")
54mm(2.13") - collector O.D. - 54mm(2.13")
152.6mm(6") - collector lenght - 279.4mm(11")
47mm(1.85") - collector I.D. at flange choke - 47mm(1.85")
685.8mm(27") - lenght of total pipe - 685.8mm(27")

now the pics:

the z6 and the y8



the primary bend



bottom view



top view



side view you see the z6 hangs alittle more.



collector view



what the inner restrictor pipe looks like i remove the one in the y8. i will be removing the z6.



so the questions here are very simple:

1. how does two d/p design different yet same length would help the powerband.

2. how does short/long secondary pipes effect your powerband.

3. what is the benifit of a long and short collectors.

and on a final footnote: over the years i've readed ppl asking if a B series down pipe fit on a D series upper primary manifold as a upgrade? the answer is Yes and No. as a plug and play no, but the pipe line up and the flange on the Bseries is a bit wider. so if you reem the downpipe bolt holes by at least a 1/4" on the two outer holes but on the innerside of the flange then yes it'll work. why?

here's the specs of a GS-R downpipe i have that i have to remove the inner pipe.

GS-R B series downpipe

54mm(2.1") - secondary pipes O.D.
51mm(2") - bend choke point
61mm(2.4") - collector O.D.
685.8mm(27") - lenght of total pipe

here's the pic of the flange. on top is a z6 and the bottom flange is a GSR.



i will say this the GS-R dpwnpipe it looks like a z6 downpipe but on steriods. lol.