Have noticed that whilst this is a largely debated topic on the US forums with lots of people recommending one brand/type over the other, there isn't much discussion and feedback from owners on this side of the pond.

A lot seem to run RCM Unequal Length pipes (UEL), indeed prior to owning a Subaru I'd always been led to believe that these were the Rolls Royce of manifolds or headers as the Americans call them.

However why do most tend to overlook equal length (EL) manifolds? Is it that they don't want to sacrifice the pulse sound they generate and many love on their Scoobies? Yet all the JDM cars have EL manifolds I am under the impression that an EL manifold is supposed to give you more torque and possibly lower EGTs as well, with some claiming a better spool over UEL and more power at the top end.

RCM 3 bolt headers are better known as GT2 Spec headers and I've read (though stand to be corrected) that all GT2 spec headers are made by one factory in Taiwan. Not sure how much truth in this so comments welcome as always. GT2 spec headers are popular in the US as they shoot for big top end power and the piping bore size on the primaries tends to be quite large. Not ideal for spool but fine for top end power.

2 bolt headers were known as GT spec although I don't know what the other differences are between the two.

At least on the 08+ 2.5L engines I've been told that the stock manifold with a good up-pipe will still flow up to 380-400hp whilst not having spool shift 400-500rpm later which happens with a tubular header due to the piping diameter. Of course whether this is an issue to you or not (the spool shift) will depend on your intended use for the car and type of driving you will be doing.

Then we have what at least I believe so far to be the true Rolls Royce of headers, the KillerB Motorsport Holy Header which unfortunately comes at a holy price too! However this is a CAD designed modern header that has moved away from where the GT2 spec has been for years, uses superior quality 321 stainless steel, short primaries and a single secondary for a 4-1 symmetrical design that gives a very fast spool whilst retaining top end power (text lifted from manufacturer website). At $1580 excluding shipping and at current exchange rates I think it's fair to say above most people's budget, although it comes with a lifetime warranty and can be ordered with Swaintech ceramic coating. Would be interesting to hear if any of the UK mappers have worked on any cars with this header?

Looking at other alternatives, Perrin make a Equal Length header with small tube primaries , 1.5 inch that is expanded at the flanges to match the Subaru exhaust port size. This design they rate to 400WHP (not sure what we feel that comes to as crank HP) and if uses a stock or smaller turbo their std up-pipe fits the bill or if running a 18/20G turbo for example their big tube up-pipe. Interestingly their up-pipes don't have any expansion joints in their design as they state to use 321 Stainless Steel which negates the need. The other nice thing about these E4 EL headers is that they are a standard 2 bolt design at the up-pipe allowing the use of either standard or hi velocity/trick up-pipes.

So after my long winded splurge above....what's everyone running on their 2.5L cars, why did you choose that manifold/header over another and would be great if people could post their header/up-pipe/turbo combination together with their peak power and torque and where they hit full boost at in the rpm range.

Proven bragging rights so to speak

 

I run RCM 3 bolt with a Harvey smith trick 3 bolt up pipe
Stock headers ( ported ) with a Harvey smith 2 bolt up pipe will be good for 400 , some guys have pushed past on this set up

Killer B. Yes the business , but you will have to remove your undertray , pretty certain it will reguire the deep pan killer sump also.

Mine has no undertray or c brace fitted , just summit racing braces so have no clearance issues.

 

mate of mine lost power with rcm headers, they seem to work alot better at higher power bands than lower.

I run gt spec gen 2 combined with a Harvey smith up pipe on mine.

 

@jazzyjembreaze and Tidgy - You running unequal or equal length? Which turbo and in 4th at what rpm do you reach 1 bar?

Killer sump isn't needed afaik , just EJ257 sump

 

mine are unequal. reality is there isn't any gains between a decent equal and unequal.

1bar? pah 1 bar is for pussies,,, lol 2 bar by 3400rpm. closed decked 2.5, V6 heads, GT2871r custom billet turbo and a whole stack of supporting mods

 

1 bar was Harveys spool measurement point

Is your 2871 stock location? Curious what your compressor exhaust housing is on that.

 

I've read alot of good things about the Harvey trick up pipe. Are they worth the extra money though ? I'm tempted to get one myself.

 

Haha I know. Was only poking fun

I'm not 100% sure on the specs, I'm up at clinic on sat so can ask, but it is stock location. Tbh it's a tad small for my engine spec hence why it never makes as good power as torque.

 

Is your manifold 2 bolt or 3 bolt? On the 2 bolt historically being the older GT spec there are a couple of different uppipes that Harvey designed. Give the guys at AS Performance a call as they have the exclusive rights to keep producing.

On the 3 bolt there is only one uppipe. Towards the end of 2012 when Harvey passed away there was a thread discussing a possible uppipe design change with the RCM GT2 headers. Am not sure if/when that happened. When did you buy yours?

I measured the Harvey 3 bolt upipe and it was just over 60mm at the 3 bolt side and around 44mm at the turbo side. No idea what the std supplied GT2 uppipe measurements are.

Those running Harvey's 3 bolt uppipe all reported better low and mid range results including a better spool. And the need to retune and adjust fuelling after fitment. There is a 4 page thread here on SN about it from 2012.

 

I'm on unequal 3bolt rcm headers with trick uppipe and on my car at 3500revs I'm getting 1.5bar on an md321h turbo with supporting mods. bear in mind I'm on a standard 2.0 sti engine so on a 2.5 with identical set up spool would be a lot earlier.

 

RCM and GT Spec Gen 2 are exactly the same. Same design, made in the same factory with the same manufacturer markings on them.

I have a pair on mine at circa 700bhp and they are fairing very well so far.

 

I reckon mines a 2 bolt mate as my headers are stock.

 

Interesting, I'll find out exactly what his were.

 

GT spec is the generic name for these kind of headers (RCM/Tomei/SC/Lateral etc) and the Gen2 was a slight design change that I read was instigated by RCM to cure leak issues on the 2 bolt at the up-pipe to manifold connection.

A Gen2 can be distinguished by it's 3 bolt design at the up-pipe.

@B9SLJ - I don't suppose you have any info on the std GT2 up-pipe as to what rpm you hit 1.5 bar at back then?