In the never ending quest for lower drag times a car tuner will often times start with removing the restrictive factory exhaust system and decreasing backpressure. A complete exhaust revamp can consist of anything from a header(s) to a cat-back exhaust system. Choosing which one is right for you is a task that must be undertaken with consideration to your local street laws.
Headers: The factory exhaust manifold is usually a bulky cast-iron unit that is designed to deliver low-end torque (provided by the small primaries). While this is desirable for daily-driving, it is not the ideal for performance. Many factors can affect a headers performance but generally the features you should be concerned with are:
- Primary Width – Wider the primaries the more peak torque (but later in the power band). There is a limit to how big is big enough that varies from engine to engine.
- 4-1 or 4-2-1 Design. A 4-1 design incorporates all 4 primaries intersecting into the collector whereas the 4-2-1 has the primaries split into twos and then into one. Different designs offer different power bands.
- Type of steel- No question here, what you want is SS for the highest quality and most corrosive resistant header(s).
While usually pin pointed as the main restriction in an exhaust, nothing can be further from the truth, while true catalytic converters do restrict flow just like anything else in the pathway of the exhaust gases; they do not hinder flow anymore than the muffler. In fact most catalytic converters are less of a restriction than a muffler. I would always opt for a high flow catalytic converter in an emissions state. These have been proven to provide a negligible loss in horsepower while still keeping it road legal.
Becuase of the budget/time that’s put into both R&D and producing a factory auto, the Yoshimura Exhaust tubing is usually a ho hum choice. Just like the stock exhaust manifold, it suffers from too small diameter piping and crushed bends. When replacing the entire exhaust system always look for a mandrel bent system (small exhaust shops cannot offer this service) that is also stainless steel. The mandrel bends are somewhat more important than the overall size of the exhaust.
Picking the diameter is a fairly easy decision and should be followed by a general outline such as this:
- 2″ Stock- Very Mildly Modified
- 2.25″ Mildly Modified-Moderate (exhaust,header,cold air intake,tune)
- 2.5″ Moderately Modified- Built N/A engine (exhaust, header, cold air intake, tune, pistons, rods)
- 3″ Forced Induction – Turbo or SuperCharged
Look for a straight through design from a respected name. Magnaflow, Flowmaster, Walker, and Thrush are just a few of the better performance muffler outfits. Glasspack mufflers tend to be a good compromise of performance at a lower price.