Maxton Design Street Pro Rear Diffuser for Subaru Impreza WRX STI Mk3 Facelift
Give your WRX STI a sharper, motorsport-inspired rear end while helping tidy airflow under the car. This Street Pro diffuser sits neatly under the bumper to add depth and a more planted look without going over the top.
Designed to fit Subaru Impreza WRX STI Mk3 Facelift models from 2011 to 2014. For other trims or years, use our vehicle lookup or check the Vehicle Fitment tab to confirm.
Made from 10 mm thick ABS plastic for strength and durability. It is impact and scratch resistant, with a UV-protective surface that stands up to sun, rain and road grime. No painting is required. If you choose to paint, apply primer first. Available in matte black or matte black with a red core. Each part carries authenticity labelling and arrives with a protective film.
The diffuser can help smooth airflow at the rear and may add a small stability benefit at speed. Expect a visual upgrade first and foremost on a road car.
- Street Pro rear diffuser
- Mounting kit
This product has TUV MATERIALGUTACHTEN certification for material quality.
Safety note: Test fit before final installation or painting. Install using the supplied hardware and recheck fixings after initial miles.
Choosing a Kit
Our vehicle registration lookup system cannot detect factory trim level. It is important for customers to check the specification of their own vehicle against the product description, and if their vehicle has an existing sports trim level, body kit or factory enhancement that may cause it to look different from other similar models.
For example: Volkswagen R-Line, BMW M-Power/M-Pack, Audi S-Line, Ford ST-Line, Merc AMG-Line, Seat FR.
These kits will not fit models that don't meet these specifications.
Returns
Purchased the incorrect kit for your vehicle? Or not sure you like the surface finish when it arrives? No problem!
Maxton Design products are eligible for return if the product has not been fitted, drilled, modified or damaged in any other way and still has the protective factory film intact. Unfortunately, there are no exceptions, this applies to fully removed and partially removed films.
Products with a protective film in place are clearly marked with this sticker, if you believe there to be an issue with the product but you can't tell without removing the film, please contact our support team directly for assistance.

DO NOT REMOVE THE FACTORY FILM UNTIL YOU'VE LINED IT UP, AND YOU'RE READY TO FIT THE PART.
See our Terms & Conditions for more information.
Installation & Fitting
Instructions & Guides
Maxton Design provide either an online reference (below) or printed instructions with their products, we can't stress enough how important it is to follow these guidelines. Not only does this create a safe, aesthetically well fitted product, but it increases the longevity and lifespan of the kit.
Neither Progressive Parts nor Maxton Design will be able to provide and support or warranty for products fitted incorrectly. For example, front splitters require the front bumper to be removed, without doing so the bolts will be incorrectly positioned and may not be able to cope with the down-force exerted on it. Straying from the guidelines in this manner must be done so at the owners risk.
Fibreglass & "Non-Prepped" Products
By adding these products to your basket you are agreeing to the below statement.
All Maxton Design Fibreglass products including certain bumpers, spoilers, spoiler extensions and skirts will require “prep” before installing.
These are not a simple 'ready to fit' modification. In transit, the items may get chipped or marked and as such prior to painting it is important you understand that the parts may require filling, sanding and repairing (defined "prep") prior to paint being applied, which can be undertaken by any reputable body shop at minimal cost.
Return requests based on not anticipating the definition above are not accepted, please be aware you have agreed to this statement and the definition of “prep” work required prior to purchasing.
Product images shown for sale often indicate a finished product, the colour shown on the vehicle is for illustration purposes.
Fitting Manuals
Please note, Maxton Design products are only available for UK shipping.
Including Northern Ireland, Scottish Highlands and Channel Isles. Delivery fees apply.






