What is a stroker motor?

A stroker motor is any engine that has been modified to increase its displacement by extending the length of the piston stroke. This involves changing the crankshaft, and possibly the connecting rods and pistons, to increase the maximum combusion chamber size inside the engine. Compression ratios may also be changed, or the design may involve using additional parts to negate this. The net result is usually an engine with significantly more power than the regular engine but lower revving.

A 'bored' engine is an engine that has larger-than-factory pistons installed in it. This involves machining the piston chambers in the block to a larger size, and the installing oversize pistons to match. This again increases the displacement of the engine, and allows the user greater flexibility in choosing their overall compression ratio. The intention, again, is to eke more power from the engine.

If both of these methods are used on an engine, the engine is said to be 'bored and stroked'. Since performing one process usually takes a significant amount of labor, many people find that they may as well do both. Also, people who really want the power are likely to really want to do both. Both methods involve modifying the lower half of the engine.

The stroker motor is an extreme (and extremely expensive) method of increasing power; it is not a popular mod on DSMs or any other car because of the high initial expense, overall complexity and relatively small margin for error. 

One little-known but useful fact for overbore proponents is that Mitsubishi sells factory overbore pistons. 1G owners can purchase 0.25mm, 0.50mm and 1.0mm overbore - 0.50mm and 1.0mm overbore are available in 2G style. Since the pistons are interchangeable between 1G and 2G engines (with accompanying changes in compression ratio), these provide additional options to the engine rebuilder. The best part is price - at the time this page was last updated the cost for the 2G pistons was less than $40 ($US) each.