Neilo

Can anyone explain to me which performs better? and why?

WRX_Rich

iTrader: (5)

bttt for you neil

I was told my old 421 x force manifold would deliver better spool up than your more average 4-1 but loose some top end

was never sure if it was down to being a smaller diameter uppipe or not as my RCM manifold seemed to have quite a bit bigger uppipe

p1mark

Purely relating to my experience on tuining NA bike engines and not subaru or turbo specific at all -

A 4-1 tended to give the best top end at the expense of a little bit of mid range. 4-2-1 was the opposite, better at lower throttle openings, pulled out of corners better and dropped the torque down the rev range a bit but always semed to be a few BHP shy of a 4-1 in headline figures.

Very general comment and was dependent on a number of other factors as well as the overall layout (primary length, pipe diameter, tapered or straight headers, balance pipes, cam timing, intake trumpet length etc...etc...)

dowser

You can't compare turbo and non-turbo header applications. Pipe diameter makes the biggest difference on Subaru turbo headers IMHO. Larger will give you better top end at expense of spool, smaller better spool but limit things at higher revs.

They need to be matched to your turbo's capabilities too (ie; good header for a td04 to vf23 type size will be too restrictive for td05 and up).

All IMHO of course

Richard

WRXTek

4-2-1 headers have better spool
4-1 headers have better top-end
equal length headers debatable more power and efficient (loose boxer rumble sound)

I'd go with the 4-1 header, lag is just over-rated