I've done the tumbler delete mod as well, makes a big difference - but as it's inlet based not exhaust didn't mention it! For headers (exhaust) ported are fine up to 400, matched up-pipe will aid spool as well, similar effect to C.J's insert. Harvey Smith has done a lot of research and has a range of up-pipes to suit different engine/turbo characteristics.
If anybody wants a set I have a spare set of tumblers that I can do the delete mod on and will let people have on an exchange basis, These are new age UK models only I believe.
Morster is correct that I'm running the Spec C manifold due to me forgetting the tumbler deletes I'd made and only realising once the car was in bits at C.J's!
The tumblers close and restrict airflow at idle and create turbulence to improve emissions but cause a restriction in the inlet on normal running, car is fine without them (will throw a Cel and can cause limp mode if not mapped out). Switching to silicone inlet, spec C manifold and Harvey headers and up-pipe gained me approx 500rpm of spool on my APS sr40 on the old 2.0.
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2005 Spec B 6MT - KiDO tuned (~270Bhp)
Custom exhaust - Cosworth filter - Samco Intake - Tints - Bilstein B8/B6 & STI springs - SuperPro ALK - Whiteline positive shift kit, rack mounts, rear adjustable camber bushes, front ARB mounts & strut brace, 20mm rear ARB with AVO mounts, - Hardrace Gearbox and pitch mounts - Prodrive PFF7's - Front Brembos - Kenwood CarPlay - 1/2 carbon grille - STI front splitter
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