Longer exhaust duration

Most stock camshafts from production 4 cylinder engines manufactured today are ground with the longer exhaust lobe duration,or that they are ground with shorter intake durations. This can be viewed that either the Exhaust Ports or Exhaust Pipe system is somewhat restrictive, and needs assistance, or that the intake system is very efficient and cam timing can be trimmed back without a sacrifice in power, in order to maximize throttle response and cruising efficiency. There is no absolute correct viewpoint in a stock engine running at conservative RPM levels, for the sake of overall efficiency, fuel economy and a quiet smooth running engine, this staggering of intake and exhaust duration is quite common and appropriate.

High Performance is another thing entirely. Change one factor, such as the exhaust system installing headers and larger pipes and the need for that longer exhaust lobe has been eliminated. Now add to this change a different carb system and camshaft and you have really changed the equation. But, why is it that so many racers & cam grinders insist on running a cam with longer exhaust duration regardless of what equipment is used? The answer is habit, many have been somewhat successful in doing it this way and will never change unless forced by circumstances.

The best result comes when we realize that an engine is basically an air pump. Air is pumped in and out and there are problems when one side or the other is restricted. Balance and flow is our objective, unless you are NOT trying to make more horsepower!

Most experienced Tuners run a single pattern cam, equal on intake and exhaust duration. This type of designed cam always make more torque.

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