header design with sequentially siamesed exhaust ports?
header design with sequentially siamesed exhaust ports?
(OP)
I was wondering about the impact about the odd heads on my engine on header design. I have a (Subaru) H4 - 16v (gasoline, spark ignition, naturally aspirated) engine. The exhaust ports on each head are siamesed together. The firing order however fires left front, back, then right front, back, resulting in the siamesed exhaust ports getting two "fires" sequentially. My question is how would this effect primary diameter and length calculations if it would?
Another question is I've seen primary lengths of around 38 inches to around 60 inches when tuning for around 3500 rpms. Any ideas as to which one is more correct and why?
Thanks
Another question is I've seen primary lengths of around 38 inches to around 60 inches when tuning for around 3500 rpms. Any ideas as to which one is more correct and why?
Thanks





RE: header design with sequentially siamesed exhaust ports?
but the old BMC 4 pot engines had siamesed ports, and the way they got round it ,was to have an exhaust called an L.C.B
long center branch,
the middle primary was way longer than the end ones.
the middle took 2+3 pots in one pipe, so was made longer to compensate,
the length of the pipe/s was made different for different rev bands/engine spec
might be of some help to you
regards Marcus
RE: header design with sequentially siamesed exhaust ports?
To get my problem across a little better...
my engine (drawn horribly in ASCII art) looks like:
front
____________
| 2 | O--||--O | 1 |
|----| || |----|
| 4 | O-||-O | 3 |
''''''''''''''''''''''''''''''''''''''''''''
back
(Clearly there's a reason they don't manufacture engines out of variable width font..)
The firing order is 1-3-2-4, however the exhaust ports in cylinders 1 & 3 are joined and cylinders 2 & 4 are joined.
RE: header design with sequentially siamesed exhaust ports?
The Subaru fires 180 apart and unless it's supercharged, I see it as a problem in flow and tuning. I don't know anything about the flat four save I drove a WRX on the track at Vegas a few years ago and I really did not like it and it's crappy five speed gearbox. Personal opinion.
Rod
RE: header design with sequentially siamesed exhaust ports?
http:
If your heads do indeed have a shared port, how far back into the head is the port divider? Oldsmobile V8 engines had a shared port for the center two cylinders on each head. The hot rodder trick was to weld a piece of steel onto the header flange that protruded into the head and kept the ports separate. Granted the seal isn't air tight, but it doesn't need to be to get the tuning performance.
ISZ
RE: header design with sequentially siamesed exhaust ports?
RE: header design with sequentially siamesed exhaust ports?
Is a head swap out of the question?
I was quite saddened to see Subaru revert to single exhaust ports per cylinder head like they'd had before 1990. At least they didn't revert to siamesed intake ports too!
RE: header design with sequentially siamesed exhaust ports?
Cool, someone's heard of them.
Is a head swap out of the question?
I've considered this before, however the older model heads possibly flow worse.
I was quite saddened to see Subaru revert to single exhaust ports per cylinder head like they'd had before 1990. At least they didn't revert to siamesed intake ports too!
Yeah, the siamesed intake ports must have sucked. Good thing they only did the single port exhausts with the 96ish-01 2.2Ls.