by kiks » Sat Apr 09, 2011 8:25 pm
Make sure theyre made right. You would struggle to better than OEM 3.0R manifolds without a proper system for a specific rev band. The oem ones do a very good job of a good spread of power, probably better than any aftermarket ez30r header could ever dream to achieve. That k2 gear stuff is utter shit for instance.
Find a bloke who knows his shit, download your rom and check your advance and lift tables. If you're going for outright power above 4000rpm you'd be looking at a 1 3/4 primary pipes about 55 inches long from what I remember working out for a maximum power at 6200 rpm. The loss would be low down. At that length you're going to have a hell of a time passing cold emissions and shit as the cats would be so far back. If you ran catless (I have no moral quandary with this at all, go for gold I say, subaru cats are heaps of shit). 3 into 1 and perfectly equal. The further out of equal length they are the longer they need to be to compensate. Any longer than 60 inches results in losing low down power more and more. 3:1 2" secondaries and 2:1 2.5" end should work fine.
Like I said, stock pipes do an excellent job, they are near perfect for all around performance and a quiet exhast without raspy overrun and shit. Keep the stock header design and put in some high flow 2.5in 100cel cats (Genie make excellent off the shelf versions that shouldnt throw CEL's according to heresay and fairy whispers).
Keep a small resonator in the centre, it sounds like a cross between a porka GT3 with a throat infection, and a hive of angry bees if you have no centre resonator of any sort.
I'd love to know the specs on ez36r cams to know what can be done for exhaust AVCS. There would be some funky shit going on to make them right I imagine.