STI JDM Rear Diffuser ( Part Number:STI ST91225FE000)

STI JDM Rear Diffuser

MODEL # STI ST91225FE000
Manufacturer Part # ST91225FE000


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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
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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.


Verified Purchase

A need for the GD Chassis
tehaviata88761 12 days ago
All I can say is it really completes the rear end for me. It looks great and it's easy to fit. Depending on your exhaust you will need to trim it. I have a Tomei Expreme Ti and it does clash. If you don't trim enough you'll get a horrible vibration noise as you come back through the revs so defintely give the exhaust at least 1/2 inch clearance.

Verified Purchase

04 STI
illysti 3 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 3 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 4 years ago
Looks great on the car! Love it! Thank you rsd
Verified Purchase

simply awsome
chrispy bacon 4 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 !!

  • Q: 2005 sti diffuser  Marsden87 4 months ago


    I want to purchase the diffuser for my 2005 impreza sti; but as you noted, it needs the bolts and frames/mounting plates. Do you sell this as a complete package and how do i ascertain the cost?

    • A: As noted in the product description: 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

      Josh P. 3 months ago
  • Q: Bolts  coffey171878590 7 months ago


    Does this come with new bolts also?

    • A: No, the bolts are not included. You would need x4 SUB 901000365SUB. You will also need CUS 673 487 A and CUS 672 487 S if installing on a 02-05 WRX or 04-05 STI.

      Evan M. 7 months ago
  • Q: Fitment  07RS 8 months ago


    What all would it take to get this to fit on a 2007 Impreza?

    • A: We do not have a confirmed fit for 2007 NA Impreza models and it would likely require custom brackets and installation.

      Nick S. 8 months ago
  • Q: Suitable for 2006 WRX Wagon  Jackie.C 9 months ago


    I would like to know, is it fit for 2006 wrx wagon thx a lot

    • A: This is not confirmed for the 2006 WRX models.

      Nick S. 9 months ago
  • Q: Fitment  Sonic yellow wrx 11 months ago


    Will it fit my sonic yellow 03 wrx

    • A: To allow this product to fit you will need additional hardware, such as the following quantities of each of these part numbers. 1x CUS 672 487 S 1x CUS 673 487 A 4x SUB 901000365

      Nick S. 11 months ago
    • A: Can i get the adiditonal hardware on rally sport direct

      Sonic yellow wrx 11 months ago
Subaru Impreza
WRX STI 2004, 2005, 2006, 2007WRX STI Limited 2007WRX 2002, 2003, 2004, 2005