Editing Two-stroke engine (section)

====Loop scavenging====<!-- This section is linked from [[Exhaust pulse pressure charging]] -->
[[File:Ciclo del motore 2T.svg|upright=1.3|thumb|The two-stroke cycle
{{ordered list
| Top dead center (TDC)
| Bottom dead center (BDC)
}}
{{legend|#10ff00|A: Intake/scavenging}}
{{legend|#639eff|B: Exhaust}}
{{legend|#ffae21|C: Compression}}
{{legend|#f00|D: Expansion (power)}}
]]
{{Main article|Schnuerle porting}}
This method of scavenging uses carefully shaped and positioned transfer ports to direct the flow of fresh mixture toward the combustion chamber as it enters the cylinder. The fuel/air mixture strikes the [[cylinder head]], then follows the curvature of the combustion chamber, and then is deflected downward.

This not only prevents the fuel/air mixture from traveling directly out the exhaust port, but also creates a swirling turbulence which improves [[combustion efficiency]], power, and economy. 
Usually, a piston deflector is not required, so this approach has a distinct advantage over the cross-flow scheme (above).

Often referred to as "Schnuerle" (or "Schnürle") loop scavenging after Adolf Schnürle, the German inventor of an early form in the mid-1920s, it became widely adopted in Germany during the 1930s and spread further afield after [[World War II]].

Loop scavenging is the most common type of fuel/air mixture transfer used on modern two-stroke engines. Suzuki was one of the first manufacturers outside of Europe to adopt loop-scavenged two-stroke engines. This operational feature was used in conjunction with the expansion chamber exhaust developed by German motorcycle manufacturer, MZ, and Walter Kaaden.

Loop scavenging, disc valves, and expansion chambers worked in a highly coordinated way to significantly increase the power output of two-stroke engines, particularly from the Japanese manufacturers Suzuki, Yamaha, and Kawasaki. Suzuki and Yamaha enjoyed success in Grand Prix motorcycle racing in the 1960s due in no small way to the increased power afforded by loop scavenging.

An additional benefit of loop scavenging was the piston could be made nearly flat or slightly domed, which allowed the piston to be appreciably lighter and stronger, and consequently to tolerate higher engine speeds. The "flat top" piston also has better thermal properties and is less prone to uneven heating, expansion, piston seizures, dimensional changes, and compression losses.

SAAB built 750- and 850-cc three-cylinder engines based on a DKW design that proved reasonably successful employing loop charging. The original SAAB 92 had a two-cylinder engine of comparatively low efficiency. At cruising speed, reflected-wave, exhaust-port blocking occurred at too low a frequency. Using the asymmetrical three-port exhaust manifold employed in the identical DKW engine improved fuel economy.

The 750-cc standard engine produced 36 to 42&nbsp;hp, depending on the model year. The Monte Carlo Rally variant, 750-cc (with a filled crankshaft for higher base compression), generated 65&nbsp;hp. An 850-cc version was available in the 1966 SAAB Sport (a standard trim model in comparison to the deluxe trim of the Monte Carlo).
Base compression comprises a portion of the overall compression ratio of a two-stroke engine.
Work published at SAE in 2012 points that loop scavenging is under every circumstance more efficient than cross-flow scavenging.