2.5 RS Question

[Pocket_Rocket]

Before I get into this, the car can not be traded.. The car can not have an engine swap.. Please offer other suggestions..

Ok.. My nephew has a 2006 Impreza 2.5 RS He wants to get some more power out of it.. Can anyone tell me what can be done?

He has an intake currently and thats it.

Thanks for your suggestions.. and again the car can not be traded or have an engine swap.

[Honest_Bob]

Intake, header, exhaust. Thats pretty much all you can get out of them. :o
On the upside I do beleive they handle better than a WRX. After the exhaust and header do some work on the suspension and it can be a very fun car to drive.

[4g4d4u]

might have better luck on rs25.com or nasioc.com they are subaru specific. but i second what honest bob said

http://www.rs25.com/forums/showthread.php?t=47973&highlight=individual+throttle+bodies

whitey says"

its actually easier than most people think to build them...the hard part is tuning them and engine management.

Suzuki GSXR 1000 or GSXR 1300 throttle bodies can be seperated as 4 seperate throttle bodies or bolted together from 2-6 inline throttle bodies...you would need to make a throttle linkage setup that synced both sides together since youd be using 2 on each head..and most likely a bracket to make the throttle bodoes stationary so the linkage dosent tourqe the t/b's when you apply throttle...youll need a vacumn log to split vacumn from each side..you can use the factory suzuki injector bungs for better atomization of fuel(just need to port the injector bung a little to fit car injectors)...also..you can use the stock suzuki tps..you just need to connect the wires accordingly to your factory tps wires.

im not sure of engine managment..probally somthing self tunable so you can mess with fuel maps.

a wideband is a must.

to make any real power id suggest some higher compression, cams/valvetrain, EL header, lightweight flywheel, injectors, rails, pump, and youll need a clutch..maybe even look into converting to OBD1 due to its ease of tuning.

get a set of GSXR 1000-1300 ITB's and a spare 2.5 RS intake manifold and start fabrication...the vacumn manifold/log can be had for $25"

[Renegade_]

the most power you'll get out of that motor is cams and a tune

IHE doesnt really do anything

[xEJ20x]

Cobb is bringing out an AP reflash for the 2.5RS.
And I believe they have a set of cams too.

[Renegade_]

or you can send out your cams for a regrind at delta cams, its 65$ per cam

[teh DIRT]

quicker- first get engine management then cams and exhaust....i wouldnt even do an intake personally.

cooler- SWAP IT! or let me turbo it!

[SUB2.5RS]

Hey a turbo 2.5RS sounds like fun. :banana:

[xEJ20x]

Time to start askin around and collecting stock WRX parts.

[Pocket_Rocket]

All...

Appreciate your feedback. I gave him the list of things he could do and also the URL and phone for Cobb. I also ordered the Subaru performance parts booklet for him. I am sure there are other better cheaper options but he is not on the internet so its just easier this way.. I am from TN orig and they are still a little behind down there..

Thanks again...

[S4toSTI]

might have better luck on rs25.com or nasioc.com they are subaru specific. but i second what honest bob said

Yeah thats intelligent now try to be helpful next time.

Anyway headers exhaust intake a tune cams there is lots of stuff to do. He could always do a turbo on that engine people do that all the time.

[xEJ20x]

might have better luck on rs25.com or nasioc.com they are subaru specific. but i second what honest bob said

You may wanna check and see what the majority of members here drive.

[Renegade_]

This is long you may want to print it out and read at your leisure. I will revise as new information is brought to my attention (note: red text is the revision)

August 07, 2006 Update: Rallitek Header + Exhaust Dyno

How to get power out of a N/A Subaru motor.

This information is based on a reasonably extensive search of this site and specifically the N/A forum. Thanks to Matt Monson, Patrick Olsen, SOLUTION, Slack and several others for there pioneering efforts.

Im sure many will chime in with corrections but here goes:

Cold Air Intake:

Cobb’s Intake is the consensus leader with clear HP gains in the 10 hp range.
Cobb sells the intake for $279 and they can be found used in the $100 range.

Injen makes an intake as well, they have models that fit 2.5L 98-05 RS’s
The only dyno I could find was for there WRX intake which gave +12 hp.
Prices are between $250 and $280 new and in the $150 range used

Ebay Intakes are cheap and have been dyno’d to be competitive with the Name Brand Intakes. http://forums.nasioc.com/forums/show...ay+intake+dyno
They generally require some minor corrective work to fit properly.

EXHAUST:
There are numerous exhaust and muffler combos out there. The general consensus is that the largest diameter you want to use is 2.25”. The typical power gain is in the 10hp range. The biggest Issue is really how loud a particular combo is.

The best bang for the buck is to find a reputable custom exhaust shop and work with them to build an exhaust to your specs. Quotes I have gotten are in the $300 range. Keep in mind this is a mild steel piped exhaust with a Magnaflow or similar muffler and hi flow cat.

Cobb / TWE and Rallitek along with several other suppliers offer Stainless Steel setups for $500 - $800 dollars new. The benefits are obvious. These setups can however be found used on NASIOC.COM and RS25.com fairly frequently so some patience will save you some money.

OBX on ebay, Sparktec is the store, sells a Cat Back exhaust for $275 + $75 shipping. IF it is built like their other products then it will likely need some work to get everything to fit. This post illustrates the possible issues.
http://forums.nasioc.com/forums/show...2&page=3&pp=25

HEADERS:
Headers are the next step in the exhaust / power upgrade ladder. There are two types generally. Unequal length headers, used on most N/A subarus until the ’06 model. These are attributed to giving the Subaru its distinctive “boxer rumble”. They are generally believed to be less useful for generating power.

Equal Length headers apparently improve exhaust pulses and significantly improve power. The loss or reduction of the boxer rumble has kept many Subaru owners away from EL Headers. Typically a good resonator in the midpipe will restore the “rumble”.

Borla sells both a single port and dual port unequal length header. The Borla header is renowned for its enhancement of the “rumble” that makes so many Subaru owners pants tight J . Early versions had some issues with cracked welds but newer generations have apparently solved this problem. The Borla header is available for around $300 new and $150 used.

COBB / Rallitek sell an EL header that appears to be of a similar design. Dyno results indicate an avg gain of 12 - 15 hp but gain results for bolt ons depend heavily on supporting mods, intake, exhaust, cams, etc. Both of these headers replace the stock cats with a new cat section as the routing of the pipes is changed significantly from stock. Cobb gives some dyno information here:
http://www.cobbtuning.com/impreza/im...rformance.html
Cobb’s EL Header runs $650 w/o a cat, add $100 for hi flow cat
Rallitek’s EL header costs $700 not sure on the cat status.
Used both can be found in the $400 -$500 range.
Picked up a COBB header w/ hi flow cat and thermal coating for $400 from RS25.com

Rallitek EL Header Dyno
http://www.rs25.com/forums/showthre...ed=1#post890856

TWE sells a EL header designed to work with the stock exhaust routing which can be handy. Power gains appear to be on par with the competition. Cost of these headers new is listed at $950 plus $460 for a hiflow cat section if you want it. Used price is commonly around $750.

MRT also sells a EL header on there site. After doing the conversion it appears to be $440 US. I dont believe this includes shipping as you have to put in credit card info before that is calculated.

Patrick Olsen's MRT vs OBX dyno thread, good read.

ENGINE MANAGEMENT
EM comes in a couple of forms piggyback, standalone and air-fuel controller. Each provides diffirent benefits and different costs.

S-AFC is the most common air/fuel controller I see used. This device is relatively easy to install some splicing may be required and only controls the air / fuel ratio at given RPM levels. As Subaru’s apparently run pig rich this little device can yield gains and provides some level of engine safety by giving the user the tools necessary to avoid running to rich or too lean. Prices new run around $250 and used ones run in the $150 range.

Perfect Power Pro is the most widely mentioned piggyback system for N/A Subaru motors. The PPP allows the user to control a/f ratios, and timing to further optimize your Subaru’s power. The biggest benefit to the PPP IMHO is the ability to adjust the timing and a/f as you add mods to your motor. The PPP comes with software to use a laptop to adjust engine maps to meet new requirements. Also Rallitek will provide you with 2 maps if you provide your cars specs to them when ordering. The PPP costs $440 from Rallitek and this includes 2 maps and tuning software. It is generally believed that the PPP adds about 10 hp to your current setup. Warning: the following thread should be considered before purchasing / installing PPP.
http://forums.nasioc.com/forums/show...t=cracked+coil

One word of caution the PPP requires that you splice the piggyback into your ECU wiring harness. This may deter some from using it but I believe a competent shop or friend could help if this is the case. Rallitek does offer a PnP harness, this is only available for ’05 / ’06 models according to their site.

Standalone systems such as linx and hydra give the user full control over the engine. These essentially replace the stock ECU. These systems require a fair bit of user knowledge from what I can tell and are quite expensive, $2000 - $4000 depending on capability.

[color=red]For the those of us who like to tinker, there is the megasquirt system. Essentially a stand alone system that you can build from scratch to meet your exact needs. The basic kit starts around $250 and provides full control over a/f ratios, timing advance, IAC control etc. Check out http://www.megasquirt.info/ for more information.

I forgot the I-speedusa ECU reflash. This seems to be effective for many ppl. You give I-Speed your ECU and mods and they reflash the chip for additional power. As you add mods you will have to update the reflash. The initial license for N/A apps is $350 with the updates at $125.

New information is out on the COBB Accessport for NA cars. Se the following threads, we'll be watching. http://forums.nasioc.com/forums/show....php?t=1034195

On to bigger projects

CAMS
Cams provide more aggressive power curves by changing lift and duration of the valvetrain. They generally come in 3 flavors: Street/Stage 1, Spicy/Stage 2, Race/Stage 3. I will really only address the first two and the race versions tend to make the car less than streetable. Changing cams also requires a decent level of comfort with pulling your engine part. Generally it helps to remove the engine and partially disassemble the heads. Power gains are significant, 15 – 18 HP.

Where the gain is realized is determined by the “stage” of the cam. Street cams provide power in the mid and upper range of the redline. Spicy cams provide most of their gains after 4000 rpms and can benefit from raising the redline. This however requires additional upgrades such as stronger springs and EM. There is some debate about this however. I have not seen a definitive answer to this issue.

COBB and TWE both offer cams at both levels. Both require a core return. Your intial outlay will be $900 for the COBB cams, then a $400 refund when you return your old cams to COBB. TWE sells both levels for $540 for SOHC versions.

A common route for cams is to have them reground to specific lift and duration. Deltacams is the most common and trusted supplier of regrinds. Keep in mind this requires you send them your cams (engine no worky) and they send them back modified. The process requires they weld new material on to the existing cam and regrind the material into a new lobe. Delta carries two grinds last I checked that correspond with the “street” and “spicy” monikers. The beauty of the regrind is that it cost about $75 per cam. So a SOHC owner spends $150 for improved performance. An interesting thread on Delta's 220 grind

Labor for cam work can be expensive so search around a fellow NASIOC member in your area may be able to help.

PORT AND POLISHED HEADS

Port and polished heads provide better and greater airflow for the combustion process. This translates into more power. Coupled with a/f control, cams, intake and exhaust mods significant power gains are possible. Generally port and polish assumes a multi-angle valve job.

Again this procedure requires that you remove your engine from the car and take the heads completely off the motor and disassemble the heads completely. Then send the heads to folks like Crucial racing for the work.

This procedure follows the typical 3 stage format. As before Stage 3 is intended for the track and is likely to make the car difficult to use as a daily driver. It also is likely to significantly reduce low end power and require stand alone EM to be worthwhile.

COBB sells stage1 heads for $1375 assuming you send them your heads otherwise there is an $800 core charge.

TWE offers all 3 levels of head work. Stage 1 is $1500 and Stage 2 is $2000. The valve job is extra at $250.

Most other vendors charge between $1000 and $2000 for similar work. HP gains are highly dependent on supporting mods. EM is also very helpful as this work coupled with intake can begin to make Subaru’s running very lean (not good) at higher RPMs.

I have seen used heads with this work already done for sale but generally they are not any cheaper than having the work done to your existing heads. I have also pulled good heads from my local junk yard for $100, so you may be able to avoid having the car out of commission for extended periods.

One final note on this subject, I have spoken with ExtrudeHone about their process and its cost. They claim similar gains and charge $600 to ExtrudeHone a set of 4 cyl Subaru heads. I don’t have any information on power gains, anecdotal or otherwise.

INTAKE MANIFOLD

Swapping the intake manifold is another power gainer that is available to the owner willing to put in time to figure out how to do it. The consensus is that the ’04 and ’05 intake manifolds provide better air flow to the cylinders and therefore more power. Pricing on this is all over the board as these are OEM parts and also available from salvage yards.

The biggest hurdle appears to be the retro fitting of the newer intakes to older EJ25 motors. For the ’05 intake look here:
http://forums.nasioc.com/forums/showthread.php?t=976482

Extrudehone also works their process on intake manifolds. If you search COBB’s site you will see that their initial N/A build project car used an ExtrudeHoned Manifold. Again I don’t have any data on the benefits of this process. The pricing from ExtrudeHone was $300.

HIGH COMPRESSION PISTONS

This is the big dog of mods. Not necessarily because of power gains, of which there are good ones, but because of the work necessary to do this. The pistons raise the compression of the EJ25 from its decent 10:1 ratio to some where near 11.2:1 for street purposes. Anything beyond this requires high octane race gas to run correctly as well as standalone EM. At the 11.2:1 level the motor will require good quality premium all of the time. It has been brought to my attention that 12:1 compression may be the safe limit for 93 octane use. But a quality EM system is highly recommended, otherwise engine may BOOM!

This mod usually requires that the bottom end be beefed up. This means better main bearings, better rods and forged crankshaft for reliability. The pistons themselves cost around $700 -$800. TWE shows $719 on their site just for the pistons. The additional block work and parts will likely run another $700 - $800 assuming you do the assembly.
Additionally some owners are using the Sti’s EJ257 block as it has the necessary reinforcement already. New Sti Blocks cost about $1700 though used ones can be had for around $1000.

Exerp from http://forums.nasioc.com/forums/showthread.php?t=1022154

[UnderPoweredRS]

CAI(cobb is best for the 2.5rs) Eq length headers pullies and a reflash from me :-D

[VolantGC8]

Wow I can't believe nobody posted the Kartboy Short Shifter and bushings. That definitely makes driving a lot better in itself. Otherwise I'll try to rattle off a bunch of things(obviously some repeated but I'm just doing it to make sure I don't skip over anything)

Cobb intake, borla header, random tech high flow cat, stromung (or whatever cat-back of choice), Kartboy short shifter and bushings, Sport clutch and lightweight flywheel (Exedy or ACT), struts (KYB AGX's), springs (P1's, Eibach, SPT, Whiteline), Bigger sway bars (most people just beef up the rear to start with), solid endlinks, better tires for sure (Pirelli P Zero Nero, Toyo Proxes4 so on and so forth), 17s with stickier rubber as well, and I guess if it comes down to it go for cams.

IMHO the intake, header, high flow cat, cat-back system and short shifter will make for a nice punch, while all the handling mods speak for themselves in the twisties.

Also don't forget that making a car faster will require better braking performance which comes with better tires first and foremost and stainless steel brake lines, better pads and rotors or if you want to go bigger than stock there's the 4/2 pot like the WRX's and other cost efficient ways. And if you have a lot of money just blow it all on a BBK.

Good luck and have fun! Hope this helps a little :)

[Renegade_]

The short shifter does shorten throw, and the bushings do tighten it up, but it you still gotta replace the linkage because the bushings would be close to gone at this point in the car's life. I am planning on doing this sometime because the bushings still don't get rid of all the wobble

[jkjersey]

Cobb is bringing out an AP reflash for the 2.5RS.
And I believe they have a set of cams too.

I just saw an article in some new issue of the gains they got out of the Cobb AP reflash now available for 05/06 RS 2.5 engines.

Sick gains. Thing was doing close to 170 whp. I think the only thing the test car had on it was an intake and exhaust.

I wish they offered this for older RSes. My brother has one and could use the signficant bump in power.
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Impreza GC8 JDM STI VI conversion
05 MCS

Drop by my page @ http://www.myspace.com/jkjersey

[Renegade_]

Stop posting with that annoying **** in the post - seriously, there is a reason why there are no images in sigs allowed

[RyanG]

since you have the intake. header,exhaust etc etc. with basic mods we were able to pull a 14.9 out of just bolt-ons on our GC. Your times may vary due to the heavier chassis. Why not nitrous?