EGR Valve:Like the catalytic converter, an engine's EGR (exhaust gas recirculation) system is designed to reduce nitrogen oxides. It does this by recirculating a small portion (5-10 percent) of the engine's exhaust gases back into the intake stream and combustion chamber. In theory, the EGR system might sound like a bad thing at first, diluting the intake charge with hot, crappy exhaust gases. But it's not. In fact, by diluting the intake charge with chemically inactive exhaust gases, combustion temperatures are actually lowered. The inert gases don't actually do anything once inside the combustion chamber but occupy space. They can't since they're inert. Lowered combustion temperatures are better for performance and they also help reduce nitrogen oxides. A win-win, for the EPA and for you. The less heat that's given off to the cylinder head, valves and pistons through thermal transfer, the more can be used for mechanical power production. Vehicles that don't use EGR valves accomplish this same end result but in a different way - through valve overlap. Many Honda engines, for example, use intake and exhaust valve overlap to trap exhaust gases in the combustion chamber, just like the EGR does. Contrary to popular belief, removing an EGR valve will actually hurt performance. It's tempting to get rid of this stuff since an EGR's vacuum connections are often the source of boost related woes, but a properly functioning EGR will help reduce knock-induced detonation through cooler combustion temperatures. EGR systems are fed either internally, through a port in the cylinder head, or externally, via a tube exiting the exhaust manifold. Either way, gases are transferred to the vacuum assisted valve that opens and closes according to engine load. Modern EGR valves are ECM-controlled, which means the vehicle's computer tells it when to open and close via a solenoid.
EVAP System:The tailpipe isn't the only place vehicle emissions can come from. Underhood gasoline vapors are just as harmful and there's a whole system designed to alleviate just that - it's called the evaporative emission control system, or EVAP. EVAP systems trap and hold gasoline vapors through a series of components. They use what's called a charcoal canister to trap the gas fumes from the tank. These canisters really do consist of charcoal since charcoal (carbon granules) is one element that can attract gasoline vapors (also carbon based). In other words, carbon attracts carbon. But the fumes don't stay in the canister; manifold vacuum draws them back out and, like the EGR system, sends them to the combustion chamber and into the catalytic converter for cleansing. A vacuum valve or computer-controlled solenoid dictates how much and when this all happens. OBDII vehicles take the EVAP process a few steps further with the addition of an EVAP system monitor that constantly tests for purge volume and leaks. In these systems the vehicle's ECM controls when and for how long the system purges. A typical purge system only works at idle and under part throttle so such systems affect wide-open throttle performance little.
It's tempting to get rid of the smog stuff. PCV valves, emissions vacuum lines and EGR valves can often complicate the power-making process and, frankly, things like a nice looking charcoal canister won't contribute to your trophy at the next car show. But there's really no reason to get rid of this stuff. Take Turbo's Project Integra for example: we're pushing close to 300 flywheel horsepower with our emissions legal Edelbrock turbo kit and completely un-tampered emissions system. Low emissions and high performance might not ever go hand in hand, but there's no longer an excuse for them not to be able to at least coexist.