This FAQ is a summary of commonly asked questions and comments that I’ve come across. Thought I would throw this together as there seems to have been an increase of 2.5i owners on the forum as of late (welcome).
2005-2009 BP/BL Subaru Legacy 2.5i
How can I get more power out of my car?
Well, this is not an easy task, there really are only a very limited number of modifications available to increase power in the N/A 2.5 engine. This is a list of “bolt-on” modifications that can net you minimal gains:
-- high flow intake panel air filter:
increase flow of air towards engine. many types available from several manufacturers. AVO filter is used with high success from many members due to its ease of maintenance (no oil required) and easy cleaning (soap + water)
-- throttle body spacer:
supposedly will allow for increased efficiency in combustion by tumbling the incoming air charge. Available from Group-A
-- lightweight crank pulley as well as alternator/steering pulleys
decrease in rotational mass of the engine will allow it to spin more freely. Available from several manufacturers, Perrin, Group-A, Cobb etc
-- intake manifold spacers (potentially has greatest benefit):
if you examine the engine assembly you will note that the intake manifold sits on top of the engine block and as such becomes very hot over the course of engine operation, manifold spacers separate the intake manifold and decrease the temperature of the incoming air. Available from Grimspeed
(diagrams taken from Grimmspeed website illustrating the concept for STi engines which feature a metal intake manifold as well along with TMIC)
Can I put CAI on my car to increase HP?????
Many inquire about the use of a CAI (cold air intake) for gains but particularly with intakes that replace the stock air box (cone type filters) it can throw off the MAF sensor and cause the engine to run too lean, or rich to compensate. Some have also run into issues with CELs. There is a more detailed article here from NASIOC:
Generally it’s not recommended and is more reliable to use a high flow filter (see above) with the stock air box. However, there are also members who have had success with CAIs, so not to say it’s impossible. Usually intakes for the Impreza 2.5RS will fit as they have essentially the same basic engine design.
Recent developments (06-2010) by AVO japan on a 2.5i platform have shown that their GT power filter kit is compatible with the 2.5i, full results still pending
“Where can I get the boxer rumble that Subaru is so famous for?” the rumble that is infamous on WRX and STi’s (also the LGT) is due to the unequal exhaust length (UEL) headers. Unfortunately the 2.5i features equal length headers and thus does not emit the noted boxer rumble.
However, there are several aftermarket exhaust options available, though they will not give your car the boxer rumble sound, they can still change the exhaust note favorably. All axleback options for the LGT will bolt right up to the 2.5i. The SPTv2 CBE has also been successfully installed on a 2.5i as well. This link http://legacygt.com/forums/showthrea...on-130408.html
contains a compilation of aftermarket exhausts for the 2.5i
Aftermarket UEL headers can be fit onto the 2.5i, but at the moment there are no plug and play solutions available. See this thread for more details on how to customize the header setup for the 2.5i http://legacygt.com/forums/showthrea...ei-153134.html
4) Suspension Modifications
All of the Legacy GT suspension components are interchangeable with the 2.5i, as such, all
aftermarket components for the LGT will also work in favor for the 2.5i
The only suspension piece that is not compatible is the front sway bar, however Rallitek has been kind enough to fabricate a 2.5i specific front sway bar. It is advisable to use reinforced mounts and brackets when installing sway bars as this has been a noted weak point in our suspension (both the LGT and 2.5i). In addition to the Rallitek front sway, it has been found that the 25mm front sway from the Subaru Tribeca is compatible with the 2.5i, more on that here:
edit: aftermarket front lower arm bars/underbracing are also not compatible, this is due to different configuration of the exhaust piping and heatshield which prevent the FSB and bracing from fitting correctly.
With regards to the OEM struts, it is generally believed the 2.5i has the same struts with slightly softer valving, but this is unconfirmed. The external housing and suspension assembly is the same however, thus all Legacy GT parts, OEM and aftermarket will bolt right up, including:
-- aftermarket struts (Bilstein, Konis, Tokico, Ohlins etc)
-- aftermarket springs
-- rear sway bar
-- strut tower bars
-- rear sub-frame braces
-- misc components (LCAs, LCA/steering bushings etc)
-- etc (they all fit)
This is probably the single greatest area that 2.5i owners can take advantage of with regards to aftermarket modifications and is likely the most worthwhile investment for your aftermarket dollars. Coupled with a set of top rubber, the 2.5i can be an excellent machine through twisties or auto-x.
LGT and the 2.5i do not share the same brake platform and thus aftermarket LGT brake components *are not* direct fitment to the 2.5i's brake system (pads/rotors/calipers are diff sizes). However, a full LGT brake swap is possible and theoretically the aftermarket BBK options (Brembo etc) for the LGT should also fit on the 2.5i but likely not necessary as the LGT brake system should suffice (particularly with aftermarket pads and rotors)
If a full swap is not something you'd want to tackle, there are some aftermarket brake pads options from Hawk and Carbotech specific for the 2.5i system. Braided SS lines from the GT are able to be swapped in as well to stiffen pedal feel. Additionally there is a Wilwood and RacingBrake kit out specific for the 2.5i that swaps the front calipers and rotors.
edit: Ion Performance has now released a slim 4-pot performance brake caliper which is compatible with the 2.5i and will fit with OEM wheels or other 17" applications
The clutch for the 5MT in the 2.5i is not interchangeable with clutch types from the LGT. Thanks to research from members here, we have found that Exedy offers an aftermarket clutch compatible with the 2.5i 5MT transmission.
KSB04 is an Exedy OEM replacement
15801 is product number for the Exedy Stage 1 clutch kit (rated to 196lb-ft torque)
FF02 is model number for the Exedy lightweight flywheel.
We have also found that the 08 GT rear limited slip differential is compatible with the 2.5i manual transmission and this has been successfully mated to take advantage of the performance and safety gains vs the open diff on the stock setup. The 05-07 5MT rear differential is also theoretically compatible with the 4EAT transmission as the ratios are the same at 4.111:1 but this has not been attempted on any cars yet.
LGT and 2.5i share a common exterior shell with noticeable difference being the 2.5i does not have a hoodscoop as we do not feature a top-mounted intercooler for a turbo. Thus installing a hoodscoop would not really be of any benefit to your engine. Additionally the 2.5i hoods are aluminum like the GT hoods, therefore there wouldn't really be any weight savings from swapping hoods (or swapping to CF). However, if you are interested in aftermarket lips spoilers or JDM conversions, these will fit and bolt right up.
Additionally the wheel sizes are the same at 17x7 with a 5x100 bolt pattern and +53 offset from the factory, earlier models ca 2005/06 came with 16" OEM wheels occasionally but aftermarket wheels for LGT in 5x100 pattern will be fine for all models; generally recommended you stay around +48 offset or higher for correct fitment, but lower offset can be done with some fender modifications.
8) Engine cont'd - “But I REALLY want to increase the power on my car, WHAT CAN I DO???”
AVO Japan has kindly been working on a low PSI turbo kit for our vehicles. The design is based of the kit that they have provided for Impreza 2.5 owners the past and has been installed successfully in many applications.
see link below for install on AVOs outback test bed:
as of 3/25/2011 the kits have been manufactured and shipped for the 2.5i, please visit AVO's website for more information:
as of 5/2011 members on this board have officially installed the turbokit on their vehicles, in particular member 1stick3pedals' thread has some useful information on the install:
Additionally there have been reports that an Accessport (for engine tuning) is available for the Legacy 2.5i now, though at this time we still await testing of the product by one of our members.
Rallitek has also put out an aftermarket camshaft kit for the 2.5i which supposedly can create gains of 20hp (crank, I believe). A tune and use of their valve spring kit when installing these is highly recommended (ie. necessary)
Rallitek does offer some other internal components that can allow the hardcore 2.5i enthusiast to really build up their motor. For most applications, I would suggest sticking with what has been laid out in points 1-6 as those are all tried and reliable options from members here.
But for more information on internals, one member here has posted logs and additional information here in this thread:
Hopefully this guide will serve as a basic map for new 2.5i owners coming to this board. I have put together this guide based on some of my experiences in modifying my vehicle. There may some editing that will be required, since I don’t know EVERYTHING but I’m hoping fellow members can chip in as the guide is really a summary of the collective experience of 2.5i owners on here who have tried many things and have discussed many aftermarket components and issues re: them. So thank you to everyone who has contributed to the N/A section over time and LGT.com as a great place for all this information.
Also special thanks to N.sane for helping contribute to the FAQ
Special thread of note: Paul Hansen from AVO has documented a number of installs / repairs on their project outback, very useful thread with excellent walkthroughs and tips.
LINK HERE --> http://legacygt.com/forums/showthrea...-1-140263.html