Stroking an engine

Many people agree with the phrase “there’s no replacement for displacement”. While technology can also accomplish this, having a larger displacement engine can produce a large gain. You may have heard of people saying, I went 60 or 30 over, on my engine’s bore. This is a machining process that is done to enlarge the engines bore to straighten worn out cylinders. While this is fun to say to your buddies it gives very little performance gain. The bore is usually kept as small as possible by your engine builder. Some engines have enough bore to hone out and could gain some power but most don’t. This is why more people are looking at stroking their engine. I would have to say that stroking engines first became popular with drag racers. This whole sport is centered on how much horsepower you can make. Many people were building big block engines then stroking them to make huge displacement engines. Companies then started realizing there was a demand and built several length crankshafts. Probably the most influential engine of all time, the chevy 350 smallblock, is a also a popular stroked engine.

 

At some point someone realized that by taking a chevy 400 ci engine crankshaft, and putting into a 350 gives you a 383 ci engine. This unlike boring, is a significant increase in displacement. Many aftermarket retailers sell these kits (crankshaft, pistons and rods) as an inexpensive upgrade during the engine rebuilding process. These kits use all the engines same outer components and look completely stock! The price of these kits is usually only marginally more than the standard rebuild. Many trucks and sports cars use these kits. A stroked engine refers to the length from the centerline of the crankshaft to the centerline of the crank pin. The rods sit on the crank pins obviously the new crank pins have to match the rods now being used. If you were to only insert the crankshaft you would have big problems. The increased reach would smash the piston into the head and possibly come down too low and hit the crankshaft. To advert this disaster either shorter rods are used or usually special pistons. The modified pistons move the piston pin up usually weigh less and have shorter skirts for less friction. All of these modifications are good when your trying to make more horsepower anyway. Stroking engines is becoming more popular all the time. Many of the import cars, especially honda, are now offering kits. This is perfect for import cars as they generally start with very small displacement engines. Many motorcycles, especially harley, and now many sport bikes offer larger displacement kits also. Probably the only downfall to stroking an engine is the fact that the piston speed has increased. Increased piston speed doesn’t have to be a bad thing as long as the new parts you have used are better quality than stock. If the parts are comparable to the stock engine pieces, it should be restricted to a lower redline. The advantages are clear and that is why many people are now stroking engines.