Emission controls and engine performance
Many hobbyists have long loathed Emissions Control Systems. For muscle car enthusiasts, the advent of Emissions Control Standards has meant poor performance and equipment restrictions. Recent legislation in California ended the "Smog Check" requirements for 1973 and older vehicles in favor of voluntary compliance.
Owners are still required to keep their factory-installed emissions systems intact, but these vehicles are no longer subject to periodical inspection for compliance. And, as you might expect, many enthusiasts have mistakenly interpreted this legislation. This has lead to the removal of emissions control equipment in an effort to improve engine operation and performance.
Much of the pre-1972 "hang-on" emission systems did little to effect engine performance. Much of the effected performance was due to the drop in compression and the switch to lower octane fuels. Design changes, such as "Lean-Burn" concepts through cam re-design, severally effected engine performance. But, to many, the added emissions equipment was to blame and that thinking has not changed much over time.
Proper engine ventilation - PCV control of engine emissions
To correct low performance and poor operation of these early engines, some hobbyists have mistakenly removed anything that they deem "emissions" related from their engines. This has included the removal of everything from air pumps to PCV controls. But, does the removal of these controls really result in better performance?
The answer is, no. The removal of emissions equipment alone, will not improve the performance of engines produced in this era. The fact is, several parts of the emissions control system serve a real benefit to an engines overall performance. The most beneficial of all of these systems, is the "Positive Crankcase Ventilation" system or PCV control.
A brief history
Essentially, engines are air pumps, both in terms of the combustion side and the crankcase side. As the pistons take in or exhaust gases on the combustion side, air needs to be expelled or taken into the crankcase to compensate for the mechanical changes in crankcase volume.
Along with air volume changes, the process of combustion creates gases that need to be vented from the crankcase. These gases are a combination of ring blow-by, oil mists, condensation and unburned fuel vapors.
Failure to properly ventilate these gases will result in sludge, rust, oil leakage and an overall loss of performance. In extreme examples, improper crankcase venting can force oil up past the rings into the cylinder, producing poor engine performance and fouling.
Early venting methods
PCV control, as is it known today, can be traced back to some of the very first combustion engines. he need to ventilate the crankcase on early engines was as important as it is today. But, before the advent of PCV controls, early engines where vented by the use of a "Draft Tube". A tube fitted to some part of the crankcase were it was routed down under the engine. As the vehicle moved down the road, air blew over the end of the tube creating a lower pressure in the crankcase. This pressure differently allowed fresh air to be pulled into the engine through a breather cap, usually in the valve cover, while expelling crankcase gases through the draft tube.
While draft tube systems worked fairly well, there were some drawbacks. They did not work well in "stop and go traffic" and they did not move enough air through the engine. Draft tube systems were fitted with oil control screens to prevent oil from being blown out of the crankcase. While the screens were effective in trapping most of the crankcase oil, some oil did make it past the filter screens. This resulted in oil being expelled on our roads and highways, not to mention coating the underside of the vehicle as well. Another negative aspect, was the location of the draft tube. Located in front of the passenger compartment, exhausted gases would sometimes make their way inside the vehicle. This, of course, was not a desirable attribute.
The passage of the Clean Air Act in 1963 brought to an end the use of draft tube systems on a national scale. Tougher mandates on engine emissions made it necessary to improve emissions control technology. The first of these improvements was the incorporation of the PCV control system. California saw the introduction of PCV controls in 1961 and in 1963 is was made a 50-state requirement.
PCV systems allow for the controlled circulation of air through the engine crankcase without the direct loss of blow-by emissions. This is accomplished by drawing in air through a filtered breather cap or more commonly, through the engines own air cleaner and circulated it through the crankcase to a point where it enters the engine intake system. This process ventilates crankcase gases and re-burns them in the combustion process, thus keeping the engine clean while reducing engine emissions by as much a 25 percent.
Why all the fuss
After attending several shows this year, it's obvious that many hobbyists and restorers are unaware of these facts. Many of the engines we looked at, lacked any type of PCV control at all. Street Rodders were the worst offenders. While their engines were all agleam, their air filters and dipsticks showed something else. They showed the effects poor crankcase ventilation and over-pressure on valve cover gaskets.
In some cases where PCV control was applied, cheap aftermarket valve covers without oil control baffles were found to be mucking up the intake system with oil blow-by. This is an important consideration to take into mind before your next valve cover purchase.
Last but not least, improper venting and control of emissions makes the engine STINKY! You all know what it's like to smell hot oil, unburned fuel and blow-by. Unless you're controlling these emissions properly, plan on having them inside the passenger area. Also, plan on oil leaks, especially around the valve covers.
We know that informed individuals will make the right choices. Therefore, we encourage enthusiasts to learn and understand these systems before taken any action that will result is improper control of engine emissions. With the proper understanding and maintenance, emissions control systems are truly a benefit to the health of your engine and to the health of our environment.