A downpipe is one of the first modifications that should be done on your car, as the OEM downpipe contains two very restrictive catalytic converters. Replacing these with our single high-flow unit will dramatically improve performance potential while maintaining the use of a catalytic converter. Our complete line of downpipes feature a high-flow, 300 cell catalytic converter, fully machined and contoured flanges and the option to add black ceramic coating.Whether you're racing time attack or to work and back, we've got the perfect downpipe for you.
We use 3D scans of 10-15 OEM downpipes to identify the variances within stock parts and ensure that our fitment is perfect across the board. We then pull those scans in 3D CAD and design our downpipe with flange locations, transmission tab locations, O2 bung locations, firewall clearances and material selection in mind. Bend locations, tube lengths and divorced wastegate re-entry point are all checked for healthy flow using CFD (computational fluid dynamics) simulations in CAD. With even the largest stock location turbine outlets utilizing factory exhaust gaskets, we used a reduction process to smoothly transition from the 2.5" turbine outlet to our 3" downpipe material. The outlet of the downpipe has a standard 3", 2-bolt flange that will mate up with most aftermarket catback exhaust systems and the secondary O2 bung that we've added will save you time and money when you decide to use a wideband O2 sensor/gauge in the future.
As engineers and enthusiasts, we take great pride in the work that we put into our design process and it shows in the finished product.
Material selection is a very important, but often overlooked, part of an aftermarket exhaust system. The tubing we chose is a thick 3in, 16ga 304L Stainless Steel tubing and our meaty 1/2" flanges will resist warping and leaks in even the most extreme environments. Stainless steel, particularly 300-series alloys, have terrific durability and corrosion resistance but are still quite cost-effective for fabrication of this type. Lower grade alloys (400 series, for example) may be more prone to corrosion over time, reducing the life and beauty of your parts while higher grade alloys introduce unnecessary cost. All flanges use a fully-machined bolt pattern to ensure very tight tolerances and flawless fitment. Each tube is CNC mandrel bent and CNC laser cut for perfectly repetitive fitment and accuracy.
The catalytic converter that we've selected is custom sized and utilizes a metallic substrate for increased effectiveness, higher flow and better durability than other, lesser units. We selected a 300 cell count mantel for a perfect compromise of performance and function.
This is where the rubber meets the road. Every single 02-07 downpipe is welded in the exact same master fixture. Our competitors build their welding fixtures around a single OEM downpipe. We build our fixtures to the average (found using the CAD data mentioned above) of a number of OEM downpipes and turbo/catback flange locations. We periodically re-check our fixtures using our FARO arm to ensure that heavy use and heat cycling don't affect their accuracy. Each downpipe is TIG welded by our expert welders. Don't be fooled by shiny imitations where a robotic TIG pass has been made over a wire-fed MIG weld; real TIG welding takes the skilled hand of a true craftsman. We take the structural integrity and beauty of our work very seriously and when you handle your new GrimmSpeed downpipe, you'll know it.
For those looking to take the finest downpipe one step further and wring out every last ounce of performance, we offer our 'Limited' line of downpipes. Limited downpipes use flanges made of the very same 1/2" 304L Stainless material, but are fully machined with recesses for each tube as well as a beautiful 3D contour to smoothly transition the irregular shape of your internal wastegate outlet into our divorced tube for tighter boost control. Limited downpipes also come in a ceramic thermal coated version which are some of the best downpipes you can buy for your Subaru.
NOTE: Once you have added our downpipe to your vehicle, you must be tuned. Replacing your factory catalytic converter sometimes causes a ‘cat converter efficiency’ check engine light. You can either use tuning to delete this CEL or you can use a mechanical fix. GrimmSpeed aftermarket downpipes modify OEM emissions control devices and are intended only for off-road racing applications.
TD04 Turbo Note: The IWG in some TD04 Turbos is slightly different than others for which the downpipe divider tab may need to be adjusted. It's a very simple process, but please contact GrimmSpeed customer service representatives if you have any questions.