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AA hypereutectic aluminum alloy flat top pistons and cylinders, 77mm 36hp and 40hp, 83mm big bore 40hp, 85.5mm, 87mm, 88mm , 90.5mm , 92mm, 94mm, stock and stroker, A & B for VW Volkswagen. AA pistons and cylinder for VW Volkswagen have been used by engine builders and racers for years. Stock pistons were always cast but hypereutectic aluminum alloy pistons will endure higher temperatures with less distortion than stock cast VW pistons. For nitrous or other extreme applications, forged pistons will endure more punishment. When using big bore piston sets (88mm-94mm), machining to the engine case and heads are required. Although using slip in big bore pistons sets (87mm and 88mm) can be convenient, there is a downside. If you enlarge the piston size from 85.5mm to 87mm or 88mm and do not increase the outside diameter of the cylinder, you are boring the cylinder thinner to accommodate larger pistons. Now you have less cylinder material to dissipate heat and the strength of the cylinder has been compromised. Excessive heat will want to distort the barrel and raise the oil and head temperature. Your best bet when choosing larger pistons and cylinders is to bore the case and the heads larger. 90.5mm cylinders are the thickest and will run cooler than 92's. 94mm cylinders are thicker than 92's but require 8mm head studs. 90.5's are usually for the guy who wants more power but and still run cooler. 94's are for the guy who just wants the make most horsepower and stomp everyone else. Stock 1600cc motors have a 69mm crankshaft. 69mm and 74mm cranks require stock stroke pistons and cylinders. 78mm-90mm cranks require stroker pistons. 76mm cranks can use either stock stroke pistons or strokers. If you use stroker pistons with a 76mm crank and stock cc heads, you can not get the compression ratio higher than about 7:1 due to the large amounts of deck height of pistons and cylinder. If you want the compression ratio higher with a 76 crank, you must use stock stroke pistons and a barrel shim to achieve desired deck height. Calculating compression ratios is only one of the key components if you want you motor to live. It is always a good idea to have your engine parts balanced , tap your engine case for full flow, so you can run an oil filter system, and keep you compression ratios conservative for pump gas. Keeping the oil clean and cool will keep it alive.
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