The Auto Garage - Performance 101: Exhaust
by Eric Bonneman
FeedTheVillage.com - The Auto Garage - Performance 101: Exhaust
The next step after your intake modifications is releasing the burnt byproduct just as fast as it came in. Enter, exhaust. Remember, that an improved flowing intake will create more power with more air. This air does not just dissapear, and it must be evacuated. The factory exhaust system on your car is built to evacuate the factory intake calculated amount of air. Now that we are producing more air, we must balance the system. The first step in creating the exhaust is by replacing your factory exhaust manifold with a high flow header. The header is designed to flow air more smoothly and rapidly from your engine. This reduces the "back pressure" caused by the increased exhaust that is created with your intake. You do not want to eliminate back pressure completely, it helps build engine torque. You, however, do not want it to cause a loss in power either. Again, you must find the balance with your set up. Generally you find a header designed for your application and have it installed. Now, we still have the catalitic converter and factory muffler inline, still creating back pressure. If you have not built up your motor internally, and are strictly using bolt ons for power, very little gain will be seen from the rest of the exhaust. But, a gain WILL be seen. Bringing you to part two, a high flow muffler. A high flow muffler has been known to create lots of power on large engines, and none on smaller engines. I see it as this, no matter what, from none to some, there is a positive gain, not a reduction. So, I believe that all set ups benefit from this. The last step is the catalytic converter, I currently have mine on my car, factory, I am running a micro compact with a 1.5 liter engine, and know that with the setup I have, I may start losing power by replacing this. However, as the engine gets larger, compression increases, or boost pressure is used, this becomes another choke point for your exhaust. There are plenty of high flow catalitic converters out there, that still perform its job as an emissions device, yet create better flow. There is also the option of installing a test pipe (no cat) or running a straight pipe exhaust (again, no cat). Doing this really only helps those higher powered engines, and is not recommended for street use. If you do remove your cat on a 1996 or newer vehicle, you will get a check engine light, for reduced catalyst efficiency. For certain model cars they sell O2 simulators to trick your cars computer into believing the cat is still there and functioning, eliminating the light. For those that do not have this option, you can install an anti-fowler in line of the rear O2 sensor and trick the sensor into seeing less exhaust, again thinking everything is okay. Exhaust pipe size, well there are lots of arguments relating to pipe size, my rule of thumb, match the pipe size to the header outlet size, and all should remain balanced. On vehicles with dual exhaust, an "H" pipe or "X" pipe is highly recommend, to attach the two exhaust banks to each other and help balance out back pressure, so both sides share a minimal amount, and perform equally on each bank of the engine.
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