Since the last post I have done a few things to the car. My original plan was to start with the suspension and start adding power after that. With the weather being the way it is here in Denver and the massive potholes left by two huge blizzards, I decided now is not really the time to lower the car. I have Tein S-tech springs and a Whiteline rear sway bar ready to be installed once the road repair crews have some time to work. So with suspension put on hold I decided to start amassing parts to make some more power.
The first thing I added was a BPM cross pipe and uppipe. Together BPM calls this package their "virtual header". Replacing the uppipe removes a very restrictive catalytic converter that is in the pipe right before the turbo. Having a catalytic converter or "cat" in the uppipe allows Subaru to obtain a lower emissions rating. But, adding a cat in the uppipe creates a significant restriction in the exhaust system before the turbo as well as creates the potential problem of having some of the cat material break off and get sucked into the turbo effectively ruining it. Removing it does two beneficial things:
1. It removes a significant restriction in the exhaust system before the turbo, allowing faster spool.
2. It reduces the amount of heat the turbo and all other under hood parts must endure.
My little disclaimer: I do not condone or urge you in any way to remove a working catalytic converter from your vehicle. To do so would be illegal unless the car is used off road only. BTW- The STi does not come with a cat in the uppipe, so that should say something that Subaru knows it is a big restriction.
The second part of the package from BPM is the cross pipe. This replaces the stock pipe that carries exhaust from the drivers side manifold to the passenger side manifold. BPM found that replacing this one pipe increased exhaust flow and effectively eliminated the need for a complete header system.
Below you see the stock cross pipe vs. the BPM XVR Pipe
As you can see the BPM piece is much nicer looking (though nobody sees it) and is larger diameter piping increasing the exhaust flow.
When I put an uppipe on my '02 WRX the gain in spool up and top end power was very noticeable. I had heard that the 2.0 liter motor in the early 2002-2005 WRX's responds much better to the uppipe then the 2.5 liter turbo motor found in the Forrester, Legacy GT as well as the 2006-up WRX's. The difference mostly comes down to engine displacement and turbo size. With the 2.0 liter motor trying to spool up the turbo with a big cat in the way was difficult. Increasing the displacement to 2.5 liters and spinning nearly the same size turbo is much easier for the engine, even with the cat in the way. After I added these parts I noticed a minimal gain in spool up time from the turbo, maybe about 200 RPM faster to full boost, but the real gains were found when I freed up the exhaust restriction after the turbo.
After the uppipe and cross pipe were done I focused my time, and money, toward the post-turbo exhaust. I purchased a COBB downpipe and heatshield from a vendor on LegacyGT.com as well as an XO2 catback exhaust off EBay.
I chose the COBB downpipe for a few reasons. First off they have been known to produce very high quality parts for Subarus for years. Their parts are expensive, but it's because they are well made and engineered very well. Their downpipe uses a cast bellmouth design and replaces the two cats found in the stock downpipe with either one high flow cat or none in their racing downpipe. Second the COBB downpipe has a bung in the top of the downpipe where you can add a wideband oxygen sensor. This becomes a very handy feature when you take the car to get tuned on a dyno, but more on that in another segment. Adding a downpipe to a late model turbo Subaru car is on e of the best "bang for your buck" mods you can do. The stock downpipe design is, in a word, horrible. Imagine running at full speed through a doorway. Imagine that doorway is very small and you barely have enough room to fit through it. Do you have to slow down before you go through the doorway? Of course, or you will run into the frame and hurt yourself. Now imagine if that doorway was the size of a garage door. Do you have to slow down to run through an opening the size of a garage door?
Nope, full speed ahead captain!
Ok, so the gases are at full speed through the downpipe, but Subaru designed the Legacy to be very quiet, like a luxury car. Quiet means restriction in the performance world. The next biggest restriction in the Legacy exhaust system is the mufflers. An aftermarket cat back exhaust fixes this problem quite well. There are many choices for the new Legacy in all different price ranges and audible ranges. I wanted a system that was loud and free flowing. The Legacy has always been way too quiet in the cabin for me. I normally use my ears to tell me when to shift rather than looking at the tach, but in the Legacy with the stock exhaust it was nearly impossible to tell if the car was even running. I chose the XO2 or "Ebay" catback because of its looks and its attractive price. I paid $400 including shipping for this system, where as the Perrin catback I was looking at was going to run me about $900 shipped. To me that's a significant difference. I am all about paying for quality, but I think sometimes in the automotive world people pay for brand names, and they pay alot for the name. I happen to know that nearly every exhaust system made is made in one of three places in Taiwan. Most of your "premium" brands are made right next to the "economy" systems.
I felt like, after reading the reviews on this particular exhaust system, that it was a good deal and I was not looking for a "quiet" system which was the major complaint from the people who had bought it. After putting on the downpipe and catback the car is definitely louder, but not to the point where it is annoying to me. I love the exhaust rumble of a Subaru, I could listen to a straight pipe exhaust all day long! If I don't want to hear the exhaust I just turn the radio up to level 7 and it's barely noticeable. Performance wise the car has become a rocket. Punch it in one of the lower gears and boost comes on instantly. Spinning wheels are very common with any amount of sand on the road. Punch it on the highway and 100mph comes before your ready. The car is almost scary fast at this point, and I rarely have the opportunity to even get into boost around town. But when I do have the chance, it puts a smile on my face from ear to ear. The really scary part is that I expect to get another 10-25 wheel hp from a AccessPORT and a custom tune.
Stay tuned, here in the near future I'm taking the car to the dyno and getting tuned. Expect my updates to come more frequently as the weather gets nicer and I have a track day to prepare for!
No comments:
Post a Comment