STI JDM Rear Diffuser

Part #: STI ST91225FE000
( 12 reviews )



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Brand: STI
Color: Black
Installation Location: Rear
Installation Method: Factory Mounting Hardware
Material: Plastic
Mounts To: Chassis
Mfgr. Warranty: 1 Year
Return Policy:

RallySport Guarantee - 30 Days

Items that are covered under the RallySport Guarantee offer a 30 day no questions asked return policy.

RallySport Guarantee items may be returned within 30 days of the original invoice date and must include all the original parts and contents for a refund.

The RallySport Guarantee does not apply to products that have been modified, damaged, misused or abused. All returns require an RMA (Return Merchandise Authorization) Number, and freight charges are strictly non-refundable. For more information regarding our freight refund policy, please refer to our return policy page found HERE.


Subaru Impreza
WRX STI 2004, 2005, 2006, 2007WRX STI Limited 2007WRX 2002, 2003, 2004, 2005

The STI Rear Diffuser came standard on the 06-07 USDM STi. It channels the air underneath the car to help with high speed stability. You can either purchase the diffuser alone if your car already came with one from the factory or you can purchase the additional hardware in order to bolt it onto your vehicle, such as the Cusco Diffuser Mount and Hardware.

The hardware you will need when installing this on a WRX or 04-05 STI is as follows:
1x CUS 672 487 S
1x CUS 673 487 A
4x SUB 901000365

REVIEWS ( 12 )


Verified Purchase
04 STI
illysti 2 years ago
So much easier to order it here, than from the dealer. I did have to trim it a bit to make sure it didnt hit my aftermarket exhaust. Looks great!
Verified Purchase
Looks good
tim95211 2 years ago
I admit I bought this mostly for looks, but I got the added benefit of a stiffer rear end with the Cusco rear subframe brace. Pretty good quality and fit is dead on.
Verified Purchase
Looks great!
bladesti 3 years ago
Looks great on the car! Love it! Thank you rsd
Verified Purchase
simply awsome
chrispy bacon 3 years ago
Once i got the Cusco sub-Frame bar and brackets install, this thing took seconds to install. It just complete the back end. Love it! Thanks RSD !!
Verified Purchase
02-07 JDM Rear Diffuser
cmartin 3 years ago
I installed the rear diffuser on my 2004 wrx, fitment was perfect with the bracket, remember to buy 4 bolts for the diffuser also. Pretty simple to install, also fit with my aftermarket exhaust


  • AnswerQ: 04 FXT Fitment  BeMoore1984 16 days ago

    Will this fit a USDM 2004 Forester 2.5 XT?

    • A: This will not be a confirmed fit for your vehicle. Confirmed fitments are located on the left hand side of the product page.

      Trevor C. 15 days ago

  • AnswerQ: 2002 wagon  Austin117 5 months ago

    Will this fit a 02 wrx wagon? Also, Will the cusco bracket have to be used?

    • A: Yes, this will fit a 2002 wrx per the application list. You will need the part numbers in the description above for installation.

      guest55fc85a42a8d25a9578b4ffe 5 months ago

  • AnswerQ: ??  Qsj408 6 months ago

    Do I need to purchase the bracket girl this?

    • A: Yes, here are the parts you will need for WRX and 04-05 STI: 1x CUS 672 487 S 1x CUS 673 487 A 4x SUB 901000365

      Josh P. 5 months ago

  • AnswerQ: Fitment with a DrawTite hitch?  Slowpoke842 9 months ago

    I have a drawtite hitch used to haul my tire and fuel trailer to the track. Will this diffuser accommodate the hitch the dealers sold?

    • A: It doesn't look like the diffuser would work with a hitch on the back without modification.

      9 months ago

  • AnswerQ: GC8 Fitment  iRomey 2 years ago

    In conjunction with the Cusco Rear Lower Subframe Bar, what else is needed to install this on a GC8?

    • A: 1x CUS 672 487 S 1x CUS 673 487 A 4x SUB 901000365 But some modifications might be needed as the parts are designed for the GD and we have not done fitment of this part on a GC to say exactly what is all needed or what is different.

      Kirill C. 2 years ago