Quote:
Originally Posted by Piotrsko
Couple of notes: is there room for the length you'll need under the car? Probably the prime reason OEM still makes cast headers.
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Well, I thought I might be able to get 80" before the cat... but I just did some measurements, and - bwahahahaNO. Based on not moving the cat, I have 18" from the cat flange to the centreline of the current bend, 15" from centreline of the exhaust up to the port centreline, 7" from port centreline to the top of the motor (which I'll call the max. vertical centreline for a ramshorn - there's room above but not much), 6" and change from the flange to the AC radiator, and 10" width to work with between the AC pump and where the gearbox bulges out - though I should be able to fit a pipe down the side pretty easily.
Straight pipes under the engine, with a bend up and then simple ramshorns give a max. pipe length to the cat. flange of about 18" (under the engine) + 15" (up to the level of the ports) + 4.5" (up to the start of the ramshorn) + 8" (180 degrees bend at 2.5" centreline radius) + 7" (90 degree bend at 4.5" radius) + 3" (start of the ramshorn to the port) = 55.5, give or take. About 26" short
ah well, that's what drawing boards are for, huh?
Might be able to squeeze a bit more out with some clever routing, of course. Or I could just loop everything around like a tuba, would make trying variable geometry easier I guess
Good news though, I measured the exhaust ports on a D head, they're 39mm x 28mm with a spacing of 84.5 (roughly - I wouldn't advise setting that running in a CNC mill
). Which gives a port cross sectional area of 989mm, equivalent to a 1.4" pipe. So 1.375" primaries might work, with careful port matching on the header side. Also 1.625" OD tubing can be used for primaries and still leave room to jam an equal diameter pipe between them, which opens up possibilities.