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Video Multi-cylinder Engine
Video Inl. 2-cyl. 4-stroke
Video Inl. 2-cyl. 2-stroke
Video Opp. 2-cylinder
Video 2-cyl. V-engine
Video Inl. 3-cylinder
Video Inl. 4-cylinder
Video Opp. 4-cyl. 1
Video Opp. 4-cyl. 2
Video Inl. 5-cylinder
Video 5-cyl. V-Engine
Video Inl. 6-cylinder
Video 6-cyl. V-inline-engine
Video 6-cyl. V-engine
Video Opp. 6-cylinder
Video 8-cyl. Firing Order
Video 8-cyl. V-engine
Video 8-cyl.-V-Classic
Video V-8 Cylinder Block
Video V8 Turbo Engine
Video W-8 Cylinder Block
Video V-10 Cylinder Block
Video V-10 Diesel Engine
Video V-10 Porsche Engine
Video V-12 Engine
Video V-12 Cylinder Block
Video V-12 Ferrari Engine
Video W-12 Cylinder Block
Video W-12 Engine
Video Radial Engine
Video Rotary Radial Engine

Video Multi-cylinder 1
Video Multi-cylinder 2

          A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Valve Overlap


Why do engines feature a valve overlap? The early opening of the intake valve and the late closing of the exhaust valve? In order to improve the filling of the cylinder with pure air (diesel engine) or with fuel-air mixture (petrol engine) and to improve the removal of the old gases or to reduce them consciously.

How it works

The valve overlap is the sum of the angles of opening the intake valve before TDC and the closing of the exhaust valve after TDC. If the piston is positioned between the 4th stroke (exhaust) and the 1st stroke (intake) at TDC, both valves are open. Exhaust gas and fresh gas can exchange their kinetic energies. In this process, the old gas leaves the cylinder more completely, and the fresh gas takes up its space. Because we are talking in this case of an open exchange of gases for a short time period, it only functions optimally in the speed range of the highest torque. The higher the nominal speed of an engine, the larger the valve overlap. It can amount (taking the as crankshaft reference point) up to 180 for racing engines.

If the engine features adjustable camshafts, it is possible to adapt the valve overlap to the single speed ranges. In addition, valve overlap is used as "internal" exhaust gas recirculation. 06/08               Top of page               Index
2001-2015 Copyright programs, texts, animations, pictures: H. Huppertz - E-Mail
Translator: Don Leslie - Email:

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