One of the best modifications you can make to a Mazdaspeed 3 is replacing the stock, restrictive, turbo downpipe with one that flows more air. Allowing the engine to breathe better improves boost response and more importantly it also allows you to increase the boost. Which increases the fun factor. Because racecar (that is starting to be my go to answer for everything isn’t it?).
I had researched a long time trying to figure out which downpipe to go with. Cobb, Corksport, Ultimate, OBX, there were numerous manufacturers to choose from and not only that, I had to decide if I wanted extra bungs for adding a wideband later, if I wanted to run a catalytic converter or not, if I wanted one long pipe or a short pipe with a mid pipe, it was a bit mind-boggling. I finally sat down after reading a lot of reviews and doing some reading myself and decided to go with the QKspl Turbo Downpipe ($522.99, w/catalytic converter $622.99) from Custom Performance Engineering a.k.a. CP-e.
The reasons why I decided to go with the CP-e downpipe was that I wanted to get a long downpipe (one piece) because it was less likely to develop exhaust leaks. I also wanted to run a catalytic converter (catless does provide a few extra horsepower, but I don’t want to smell like exhaust everywhere I go) and the CP-e unit came standard with extra bungs so I can add a wideband and exhaust temp gauges later on. I like to add modifications to the car that have a bit of future proofing and the QKspl checked all the right boxes.
Installation and removal of the factory downpipe is a nightmare. Ask any Mazdaspeed 3 owner which is the modification that gave them the most hassle, the downpipe would be in the top 3.The factory downpipe consists of two pieces, the headpipe and the midpipe. The midpipe comes out easy after removing two bolts and sliding off some exhaust hangers. The headpipe, on the other hand, can only be removed from the bottom of the car. That involves lots of twisting and cursing, because there is a specific way the factory headpipe has to be twisted in order for it to clear the body bracing. It was possibly the most frustrating part of the process. But once the factory stuff is out the way, installing the QKspl is a breeze, just make sure to get that downstream o2 sensor started BEFORE you bolt up to the turbo flange.
After you get everything installed and tightened down, do not be surprised if the downpipe starts smoking as you let the car warm up. There is a coating that CP-e adds to the downpipe in the manufacturing process that burns off and cures after the first startup. Mine smoked for about 10 – 12 minutes after I warmed up the car and drove it around the block, checking for exhaust leaks. Since then, I haven’t smelled anything burning or seen any smoke.
Now that I have finally installed a downpipe, I can almost begin the process of tuning. I still have a few bits to go before I can get really into the process. Living with the downpipe has been easy, although I think my neighbors might not like the cold starts in the morning, the car now pops and crackles on startup, and will occasionally do the same while driving. Throttle response has improved and the turbo pulls MUCH stronger now while under boost. I am glad that I added an upgraded RMM a while back, torque steer will definitely become more pronounced after this upgrade. I think I need to finish off this combo and get the CP-e catback exhaust as well!
Words of advisement, though. If you are going to add a downpipe but do not have a Cobb Accessport, or have upgraded High Pressure Fuel Pump Internals, I highly advise getting them first! The stock tune will run VERY lean with an aftermarket downpipe installed. After I installed the downpipe, I reflashed my ecu with a Corksport Stage II OTS tune that was a bit conservative (17.5 psi boost target) just to make sure I did not run lean until I can get a formal tune. It’s better to be safe than sorry!
Now that I have the downpipe installed, I am one step closer to my goal. But I can’t decide if I want to finish the exhaust or get a front mount intercooler? Guess its time for more research!