d.j.c

O.K. advice required from the font of knowledge that is....Equal length headers, why are they used, what are the benefits/downsides & who makes the best? Bring the replies on!

finchyboy

The main advantage that they offer is an increase in torque i have heard that it can be as much as 30 ft lbs of torque right through the rev range.
I have some X force ones that i bought from A.P.I they perform well now but i have had to totally re-engineer the slip joint fixings as all the welds cracked. So i would stay clear of them.

JimmyBFC

They are much better if you want to tune your car into something special, hence why the spec-c has them and Evo's are able to be tuned a lot higher for less money than a scoob.

You'll lose the burble, but still have a decent sound, especially if you start thinking about incorporating anti-lag etc.

nom

They are different, not necessarily better. 'Better' depends on what you are trying to do!
Most on the market these days are designed for huge flow (equal length or not), which means that the exhaust gas speed is much slower than the standard headers will give, therefore boost is later. Fine if you want masses of power, not if you want a car that is good on the road.
Equal length has far less effect on forced induction engines than NA as the momentum/suction caused by well designed ones is far less useful - want you really want - particularly on a turbocharged car - is good pulsing to kick the turbo into life fast & early, which is far easier to do with a non-equal length manifold. Believe it or not, Subaru does know what it's doing!
Choice of manifold is very similar to choise of turbo, and they should really be picked as a 'team': if you want 400bhp, pick a turbo and mainfold that can both do just 400bhp & you'll get maximum response with the power you want.
I've used MRT pipes (teeny-tiny diameter, unequal length, 4-2-1, no longer on the market), HKS (unequal length, pretty 'fat', 4-1) and H&S (equal length, medium thickness, 4-1 I think...) the MRTs were excellent up to around 400bhp - early spool, very smooth power delivery; HKS went to higher power but late spool & uneven power with a huge extra 'kick' at around 4,400rpm - presumably entering their 'efficient' area so great for track, not good for the road; HKS had smooth delivery, medium spool but became restrictive at around 600bhp. On anything up to, ooo, 400bhp at a guess, I wouldn't bother changing from the standard manifold - there starts to be a restriction at arond 350, but I wouldn't get too worried about it. Port & clean is probably a good value plan, though.

silent running

Basically, all other things being equal (excuse the pun!) you will drive a turbine more efficiently with evenly spaced gas pulses than uneven. It's exactly the same principle as getting a merry-go-round up to speed at a playground by regularly and rhythmically applying a firm shove, rather than just whenever you feel like it.

The downside is that you will lose the off-beat Scooby sound by driving your turbine more efficiently.

Please note, I am not getting into a discussion of whether 'X' equal length headers are better than 'Y' unequal headers as makes vary wildly in quality, dimensions, jointing etc. I am just saying that all other things being equal, equal length headers are more efficient at driving a turbine.

p1junkie

iTrader: (5)

have a set of perrin ceramic coated headers for sale 400.00 including aps uppipe if anyones interested

nom

Lots of evenly-spaced pulses good, but single less frequent larger ones can get things going quicker in the first place... but it depends on the size of the pulse, the space and the size of the thing it's trying to twirl - one large punch can be more effective than four little pats. With the relatively teeny Subaru engine, I find the unequal header works rather better in practice, even if technically that's wrong . However, equal/unequal is noticeably less important than tube size & 4-2-1 or 4-1 design. Small & 4-2-1 for a smooth, broad 'medium' torque curve or large & 4-1 for a higher peak but over a narrow band. In general . One is suited to a standard engine on road, the other a high-boost engine on track, so it depends what it's going to be used for.
But whatever, I wouldn't get too caught up on equal/unequal, there are more important things to consider.

Slowboy Racing

In a nutshell, what spec car you planning on using the Stainless headers on and what power are you planning on running.

The answer to this question will go along way to making a final decision on headers and the reasons why these headers will be the better choice.

silent running

Hang on, I said 'all things being equal'. You are now comparing lots of 'little' evenly spaced pulses with one 'big' pulse. I am not trying to discuss the relative merits of different makes, tube lengths or diameters, extraction effects or any of the myriad of black arts that go into proper exhaust design. Let's clarify this again...equal length headers are going to give evenly spaced pulses; unequal headers can never do this except at very narrow ranges of revs in the same way a cam can come 'on cam' at certain points and will be 'off cam' the rest of the time because it is a fixed, simple, mechanical device.

Therefore a valid comparison to make if we are broadly comparing unequal to equal headers would be; what will drive a turbine more efficiently - 4 equally sized pulses, equally spaced apart? Or 4 pulses exactly the same size, but with a couple in quick succession, then a big gap, then a couple more later on?

Not that I'd trade my OE system for an equal length one because I love the noise my Scooby makes! But I am aware that it is not the best way to drive a turbine and is a packaging compromise because of the flat layout of the engine, that happens to have a pleasant aural side-effect.

dunx

iTrader: (3)

Agreed Subaru aren't giving anything away, a road car is a cost/performance compromise, hence an EVO is £5K more....

The exhaust works well enough, and is cheap to produce, sorted !

I went for slightly un-equal from Lateral and it sounds different, but nice...

HTH

DunxC

nom

Pulse size - 'cos if you've got one unit of air volume (per cycle), 4 equally spread at .25 'units' each it may not be as effective (depending on momentum) as when they're all bunched up. But as you say, it depends hugely on every other part of the design, which is why in my opinion equal/unequal is unimportant when choosing headers compared to the other parts (runner length, diameter, etc.), so a decision shouldn't be based on it .
I still like the standard header as it doesn't appear 'tuned' to any particular airflow, so it works well on the road for a smooth drive without any sudden surges of power to unbalance the car.

silent running

Yes I think that's true, the standard system seems to work well and the equal/unequal is not as crucial as other elements of the design. So might as well keep the Scooby burble if you can.

harvey

iTrader: (48)

Ported O/E headers give a noticable improvement in torqe with earlier spool, optimising on what Subaru already planned but perfected beyond the cost and production constraints of production engineering.

172sport

iTrader: (6)

One point to note is if they are made from bog std 304 grade stainless steel they 'will' crack. If you want them to last be prepared to pay lots more because you need to use inconel.