Nissan SR20 Downpipes are like people: There are probably billions of them out there, and even more designs yet. Due to the immense popularity of the SR20, it was only natural that the aftermarket would embrace the engine design with everything from radiators to forged crankshafts. But this article is about downpipes, so lets get to it!
The whole purpose of the downpipe (or dump pipe, if you're australian) is to channel the rapidly cooling exhaust gasses away from the turbine section of the turbocharger. The idea behind a bigger downpipe is simple: Less restriction. By reducing the restriction in the exhaust after the turbocharger, the engine doesn't have to work so hard to evacuate its spent gasses. The end result is more power, torque, and potentially better fuel economy as well. An engine under less load requires less fuel to do the same work. By chosing to upgrade your SR20 downpipe, you are doing your engine a great service, not to mention your foot. The freer flowing exhaust gasses will make your engine more responsive and more pleasureable to drive. With more torque available lower in the power band, driving from light to light will be easier, and feel as if it requires less effort.
Flex pipes and flanges
There are several things one must take into account when looking for a downpipe to purchase for their SR20 engines. You'll need to ensure the flanges are correct for your turbo elbow and catalytic converter (or straight pipe, if you have no cat). You'll also need to chose between a solid pipe or a pipe that features a flex section. The flex section is said to help prevent unwanted cracking around the welded areas on the downpipe. Personally, I've been running a 3" downpipe with no flex pipe for the better part of two years and have had zero issues. It's mostly personal preference. You'll probably find opinions are mixed on the topic as well, with some saying a flex pipe is a waste of time, while others will share stories of broken welds and general headaches.
You'll also need to chose between downpipes that may or not have optional O2 bungs pre welded into the pipe. If you ever plan on picking up an aftermarket widebang gauge and sensor, I'd recomend chosing the downpipe with the O2 sensor bung. Even if you don't buy the wideband for a year, when it comes time to finally install it, you won't have to go through the hassle and expense of having a bung welded in for you at a shop.
Circuit sports SR20 downpipe
The Circuit Sports downpipe features a stainless mesh flex section, as well as a bung designed for a "fat" O2 sensor. It features 304 stainless construction and mandrel bends for maximum exhaust flow. The downpipe comes fully polished with a mirror-like reflection, and includes all gaskets and bolts required to completely replace your stock SR20 downpie.
Megan Racing Downpipe
The Megan Racing SR20 downpipe features 304 stainless steel construction, as well as a flex section to prevent cracking. The inner diameter of the pope measures in at 3", and features mandrel bends for smooth exhaust flow. The pipe comes with a mirror-like finish, and is resistant to rust thanks to its stainless construction.
Blitz SR20 Downpipe
The Blitz SR20 downpipe features full stainless steel construction, with a 3" inner diameter. The pipe connects to the OEM turbo elbow via its 3 bolt flange, and most aftermarket elbows. Blitz felt that the flex section wasn't necessary, and so left it out to simplify things. This pipe does not delete the catalytic converter, so a test pipe will be required for a true straight through exhaust.
Trust Greddy Downpipe
Featuring a mild steel construction for reduced cost to the consumer, the Greddy SR 20 downpipe features mandrel bends and beautiful welds that will hold up for years under even the most demanding drivers foot. Comes with all hardware required for a straight bolt on affair.
JVT Racing Downpipe
The JVT Racing SR20 downpipe I came across on ebay caught my eye because of the low price, the flex section, and the visual quality of the flanges and welds. Some advise against "ebay brand" parts. This is one of those situations where I would probably buy the downpipe myself if I needed it. Full stainless construction with mandrel bends make it a great choice for budget racers.
KO Speed Downpipe
I can't say much about the <$50 downpipes that you find on Ebay. I can say that it'd be a fun experiment to see how long it would last in both daily driving as well as competition. If you've tried one, let us know how it's working out for you. At under fifty bucks, it could just turn out to be the deal of the SR20 century!
The Ebay decision
With so many options for SR20 downpipes out there, it makes you wonder how anyone makes any money at all. Especially with the hyper cheap "Ebay brand" downpipes that have been on the scene for years now. The only thing I can recommend as owner and driver of a turbo car with an after market downpipe, is don't expect OEM lifetimes out of them. They'll last, sure. But they won't last for twenty years. It's just a fact of life, and probably the reason why a new OEM down pipe costs three or four times as much as a high quality aftermarket pipe.
If you plan on picking up an Ebay sr20 downpipe, let me know in the comments. Myself and may others want to hear your experiences with them. Do they last? Did it crack three weeks after you bought it? Did it arive in the shipping box broken in three pieces?