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Posted by Marty [50.68.51.62] on Monday, April 02, 2012 at 13:27:45 :
In Reply to: Re: now that we are on roll posted by clueless [201.202.24.94] on Monday, April 02, 2012 at 13:21:09 :
Undersquare engine examples
Many inline engines, particularly those mounted transversely in front-wheel-drive cars, utilize an undersquare design. The smaller bore allows for a shorter engine that increases room available for the front wheels to steer. Examples of this include many Volkswagen, Honda, and Mazda engines. The 1KR-FE-engine used in the Toyota Aygo, Citroën C1 and Peugeot 107 amongst others is an example of a modern long-stroke engine widely used in FF layout cars. This engine has a 71 mm bore and 84 mm stroke giving it a bore/stroke ratio of 0.845. Some rear-wheel-drive cars that borrow engines from front-wheel-drive cars (such as the Mazda MX-5) use an undersquare design.
Despite their reputation as low-speed torque machines, some undersquare engines are designed for quite high speeds. The Honda Integra Type R's B18C5 engine has one of the highest redlines (8,400 rpm) of any production engine, yet features an undersquare design. The 2011 Ford Coyote engine is a modern undersquare engine with a 7,000 rpm redline.
Many British automobile companies used undersquare designs through the 1950s, largely because of a motor tax system that taxed cars by their cylinder bore. This includes the BMC A-Series engine, and many Nissan derivatives.
The Chrysler Slant-6 engine, in its most common 225 cu in (3.7 litre) version, is a massively undersquare engine, with a 86 millimetres (3.39 in) bore and a 105 millimetres (4.13 in) stroke (bore/stroke ratio = 0.819), producing most of its power right on the peak of its torque curve. The Achilles heel of this engine, otherwise known for its exceptional durability, is being over-revved by inexperienced drivers. Red line for a factory engine is under 4,500 rpm; red line with aftermarket connecting rods is about 5,500 rpm. On the other hand, a well-maintained Slant-6 can be made to idle as low as 75 rpm (though this is not a recommended speed - neither the alternator nor the oil pump will function adequately).[original research?] In some circles, the Slant-6 is nicknamed "The Stump-Puller" for its diesel engine-like low-speed torque. Appropriate gearing and driving skill is required for performance use.
Willys also used mostly undersquare engines; in fact the L134 and F134 engines, with their fairly small 79.4 mm (3.125 inches) bore and 111.1 mm (4.375 inches) stroke (bore/stroke ratio = 0.714), are probably the most undersquare engines ever built (for Jeeps).
The Dodge Power Wagon, among other vehicles, used a straight-six Chrysler Flathead engine of 230 cu in (3.8 litre) with a bore of 83 millimetres (3.27 in) and a stroke of 117 millimetres (4.61 in), yielding a substantially under-square bore/stroke ratio of 0.709.
The 292 Chevrolet I6 is also under square, with a bore of 3.875 in and a stroke of 4.125 in (bore/stroke ratio = 0.939).
Virtually all piston aircraft engines used in military aircraft were long-stroke engines. The PW R-2800, Wright R-3350, PW R-4360, Rolls-Royce Merlin (1650), Allison V-1710, and Hispano-Suiza 12Y-Z are only a few of more than a hundred examples.