the single stage Snow Commander (2001-2008) & 2 stage Power Max 726TE/6000 (2004-2008); the extra horsepower was obtained using transfer ports in the piston and cylinder wall, and this model ran at the same operating speed as the 6.5 hp engines (4000rpm). Production stopped in 2011. Innovations The aluminum engine – This was introduced in 1953 as a means of having a lighter-weight engine for applications such as rotary lawn mowers. It was improved five years later in 1958 with the introduction of the Kool-Bore (all aluminum) and Sleeve-Bore (aluminum, with a cast iron cylinder liner). Easy-Spin Starting – This compression release, implemented as an extra hump on the intake lobe of the camshaft, was introduced in 1961 to reduce the effort required to start an engine. In 1982, a new U.S. federal safety regulation required lawnmower blades to stop spinning within three seconds of the operator letting go of the handle. The least costly, most common way of complying with the new regulation was to put a flywheel brake on the mower engine, to stop the engine (and therefore the blade) immediately when the handle was released. Briggs & Stratton engineers found engines with the Easy-Spin camshaft were unacceptably difficult to restart after being braked to a quick stop. The Easy-Spin lobe hump was moved to the exhaust valve, but this reduced engine performance. The intake-side Easy-Spin remained in use on Briggs & Stratton's engines larger than those used on mowers subject to the brake requirement, but was discontinued in 1997 due to tightening emission regulations. The Synchro-Balanced Engine – This 1966 innovation was designed to attenuate vibration caused by the reciprocating mass of a single-cylinder engine. The design was a series of counterweights opposing the crankpin. The Twin Cylinder Engine – This engine was introduced in 1977 as a means of competing with Briggs & Stratton's rivals, particularly Japanese firms like Honda who were cutting into traditional Briggs & Stratton markets by producing lawn mower engines (and later, complete lawn mowers). These first models were rated 16 hp (11.9 kW) and displaced 40 cubic inches (656 cc), but were joined in 1979 by 42 cubic inch (694 cc) models rated at 18 hp (13.4 kW). The original price for the version was $70 lower (at US$228) than their single-cylinder cast-iron version bearing the same power rating. Industrial/Commercial (I/C) – This series of engines, initially ranging from 3 to