The possibilities for a vehicles aftermarket exhaust are endless. That sounds a bit cliche but it’s the truth. You can have your local muffler shop fabricate almost any type of setup you could want, out of whatever parts and piping you want. Or you could browse through all the different models and styles of exhausts made by aftermarket companies for your car. It’s like being in a candy shop. In some applications, the exhaust is purely for sound, in others, it’s focused more on power gain, and in most average applications, it’s focused on both. The problem is, an exhaust is located underneath your car. It faces the elements with no protection, constantly getting bombarded by debris, dust, road salt if you live in an area where it snows, water, stones, and rocks, in addition to extreme heat from your engine, so it needs to be very well designed and fabricated. Here is what you should know when choosing an aftermarket exhaust, or fabricating your own custom design;
Material – Usually the goal here is to save weight, while providing strength and durability. Titanium exhausts are top-notch and ultra light weight, but they carry a corresponding price tag, and are best suited for racing applications. Stainless steel is the most common, and most companies will advertise that their exhaust is made out of “nuclear alien grade” etc. stainless steel. In order to test the quality of stainless steel to determine if its pure metal or mixed and prone to rust, take a magnet and see if it sticks to the exhaust. If it sticks, the strength of the pull will tell you how impure the stainless steel is.
Piping Thickness – Once you know that your exhaust is made of good material, you can’t call it a day. Piping thickness will directly affect exhaust gas temperature, and that affects scavenging exhaust gas out of the cylinders. This is why you’ll see race cars with wrapped exhausts and manifolds. Not only does it prevent heat escaping and soaking your engine, but if you took chemistry in high school, you’ll understand why keeping the gases nice and hot helps them to flow out.
Flange Thickness – Flanges are where different sections of the exhaust bolt together if it’s not all in one piece. If an exhaust has thin flanges, they could bend or warp under stress and heat over time, and eventually you’ll wind up with an exhaust leak.
Diameter – Bigger is not always better. As a matter of fact, you’re probably loosing power on your Honda Civic with the 4 inch muffler on the rear. Pressure equals Force divided by Area (P=F/A). If you’re piping is too large for your application, you could be loosing back pressure needed to scavenge gas out of the engine quickly. Do your research on the optimal sizing for your application first.
Divorced Wastegate – Divorced wastegate refers to the design of the downpipe coming off the back of the turbocharger. The point of a wastegate is to regulate exhaust pressure and release excess exhaust, therefore controlling the amount of boost. A proper divorced wastegate downpipe will have an additional opening for the wastegate, instead of forcing the gases to hit a plate and then merge at an angle with the main exhaust gasses. In addition, the best divorced wastegate designs have a separator plate between the wastegate and main exhaust so that the two are funneled down and merged later, rather than pooling at the head of the downpipe.
02 Sensor Position and Depth – Many aftermarket systems move the position of the 02 sensor, and unless they’ve tested or developed the new position (your eBay exhaust probably wasn’t), it could actually mess up your car’s tune and computer readings of exhaust gas. The closer to the factory location, usually the better. Depth also matters. If the 02 sensor isn’t inserted far enough, it could be getting an incorrect reading, and that throws everything off.
Flex Points and Joints – Flex points or joints on the exhaust are important. Your exhaust is mounted to the chassis by hangers on rubber mounts, but at the far end, it’s bolted to your engine, which bucks and moves under torque. Imagine then what your exhaust looks like straining while the engine rocks. For the same reasons you would install better engine mounts or engine dampers is why you should check if the exhaust has good expansion points or flex points, to compensate and allow the exhaust to move fairly freely.
Welds – Good, clean, thick, pulsed, high quality welds are what you’re looking for here. The point of a weld is to hold something together. Now imagine what could happen if that bond isn’t very high quality. No me boosta.
And some final tips for installing your new exhaust when you do get it; It’s a good idea to inspect the factory rubber hangers and determine if they need replacing, since it’s the perfect time to do it. Also, OEM exhaust gaskets are usually of higher quality than what comes with the exhaust, so invest in some if you need them.