Emission Controls

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Revision as of 04:08, 25 November 2006

Emission controls, first introduced in the US in 1964, have proven over time to be a good thing -- today's cars have very low emissions, but high power. However, some of the early systems were bad for performance.

Which controls can be eliminated?

For a race car, any you want may be removed -- though some are good for the engine.

For a road car, it depends on the local laws. Here are some thoughts on the technical aspects:

• Positive Crankcase Ventilation (PCV). This first of the emissions controls aims to prevent the crankcase from dumping fumes right into the atmosphere. This is a good system, and can actually helps power and fuel economy. Before 1964, US cars had a 'breather pipe' that led from the block down to the underside of the car. Normal blowby gases were thus simply vented to the atmosphere. Worse yet, when the engine rings became worn, a visible trail of smoke could be seen eminating from the bottom of the car. The PCV system consists of three components: 1) vacuum operated valve connected to the intake manifold 2) crankcase breather tube, generally from the engine block to the air cleaner 3) breather hose from rocker cover to the valve. Fumes are thus routed to either 1) air cleaner, when engine speeds are high and so able to 'suck' the fumes in or 2) intake manifold, when idling where vacuum is high and so opens the valve slightly and pulls the fumes out of the crankcase. This is where the efficiency comes in. Since at idle the pistons are operating under low vacuum, the PCV valve equilizes the forces in the crankcase, hence less oil is sucked into the cylinders at idle. Race cars are often required to use an oil/vapor seperator instead of or in addition to the PCV valve. <li>Ported vacuum for vacuum advance. Ported vacuum is the carburetor fitting tapped just above the throttle plate. This gives zero vacuum at idle, but full vacuum at just above idle. This is an OK system, no need to remove it or using full-vacuum advance. In fact, hooking up the distributor to the intake manifold can cause timing setting problems, as the standard specifications are for ported vacuum. <li>Fuel Tank vapor recovery. This is a good thing, as why let gas fumes get into the air? They are easily controlled by venting the tank and the carburetor float bowl to a charcoal cannister. See your Datsun repair manual for an explanation of the various schemes used over the years. <li>EGR (Exhaust Gas Recirculation) was fitted starting at around 1974. This one hurts performance, and should be blocked for a race car. The easiest way is simply to remove the vacuum hose and block it with a plug. For a more streamlined look, remove the EGR valve and replace it with a block plate, and the hoses that control it. For a detailed explanation of EGR, see the AutoZine Technical School article. <li>Air Pump. This takes power to run, so for an off-road car should be removed. Remove the pump, block the exhaust manifold opening for it, and block the air hose fittings that are on the air cleaner. <li>Catalytic convertor. First fitted to Sunnys around 1980 or so. The converter fits into the exhaust pipe system, and filter/converts unburned hydrocarbons (unburned fuel) into less-harmful substances namely water and oxygen. Early convertors were a restriction in the exhaust system, but newer designs have high-flow. Not too bad of a system, although some use the Air Pump to supply extra oxygen to the convertor.