hi can someone tell me the difference between equal length headers and unequal length headers besides the obvious length on one

 

the equal length get rid of the burble

 

Expandig on the above question, At what mod level do headers / up pipe need to be changed and what gains are made?

thanks

Dave

 

so am i right they do the same job but one eliminates the noise and they are required for 380-400bhp level?

 

I would guess the equal headers flow better and so are better for higher power? hence the Spec C had them is that right?

Dave

 

there is some flow rate gains using equal length, however, as i understand it, the uprated un-equal length arn't far off them and you don't loose the burble.

spending on your base model car will depend if they are needed or not, mine is a my00 uk turbo and i have still go the standard headers on there pushing 340bhp, which is as far as i'm taking it ont he standard uk engine

 

On a 4 stroke engine, 2 pistons are in the combustion stroke at any one time.

On an Impreza due to the different lengths in exhaust to the hot side of the turbo, the exhaust gas pulses from the subsequent exhaust stroke land at the hot side at slightly different times leading to the 'off beat' burble.

Equal length manifolds ensure that the exhaust pulses arrive hot side at the same time.

The difference perfomance wise could be compared to pushing a roundabout (the roundabout being the turbine wheel and the push being the exhaust pulse) the theory goes that the combined larger push of the combined pulse has more accelerative force on turbine wheel in effect causing it to 'spool up' quicker.

 

An equal length manifold allows the mapper an easier time.... but they are over £1000.... ignoring rare twin-scroll for the moment !
An un-equal length manifold keeps the burble, increases the flow efficiency to allow more power/torque than the standard manifold.

340 bhp seems about it for standard parts, 360 + with un-equal on the same engine, more with a bigger turbo. I going that way soon !

HTH

DunxC

 

IMO, headers are an improvement regardless of state of tune, whether you need them or not is a different question.

With equal length headers, there are easier to map more accurately as said above. The scavaging effect of the equal length headers is equal accross all 4 pistons, all being equal (Bore wear, valve wear etc....). With un-equal length headers, the scavaging is, well, un-equal and the only true way of tuning the engine for equal A/F ratio's is to monitor each cyclinder seperately and trim injector duty accordingly.

I'm not convinced that equal length headers move the power band further up the rev range, they will flow better higher up the rev range due to the equal scavaging and flow charataristics.

 

It's not just the length though it's about diameter and harmonics, didn't mention that in my initial post.

I might be totally wrong on this, but Subaru did not deliberately construct un-equal headers to improve power, it was simply a case of packaging,

In summary, there are headers of both types with good and bad bores etc. The guys who tune Subaruss everyday for the living will be the best people to advise on preferences etc.