When you stroke a motor your increasing the piston travel in the cylinder bore up and down.

You move the wrist pin in the piston so that the piston will travel farther down in to the cyl but not out the top.

Thats my understanding of it. Might not be right though.

 

OK, I just learned that you make a stroker by moving the wrist pin upwards on the piston.

Not quite right. You make a "stroker" by increasing the stroke length by installing a crank with longer throws. The travel of the piston increases in the downward AND upward directions by the amount of the stroke increase. It's OK if if drops down the hole farther ( to a point) but it can't stick up out of the hole any further. That's why you need to raise the pin location in the piston, so that it travel tops out where it did before the increase in stroke. HTH.

 

Right, it is the combination of the longer throw/stroke of the crank and the raised wrist pin location that makes more cubes out of the original size bore. Mfgrs. establish the cu. in. displacement goal and build an engine to that goal. Some apps. need longer strokes to provide the needed performance for torque, shorter strokes make for a higher operating engine speed.

 

Wrist pin placement is a byproduct of different measurements. IE, 1/2 Stroke + Rod Length + compression height (wrist pin) = deck height.

Raising or lowering the wrist pin does nothing to increase or decrease displacement. Take the common sbc 383 for example. It can be build with 3 different "off the shelf" rod lengths that all have the wrist pin in a different location on the piston but the displacement stays the same.

The only way to increase displacement is to add more stroke (crankshaft) and/or bigger bores.

 

Why not make every motor a stroker in the first place from the factory? Cuz it looks like "free" extra displacement.

The simplistic answer is that you can only make an engine so big before it won't fit in your Chevelle's engine compartment any more. I know, now your next question is, why didn't they make Chevelles bigger. Do you remember the energy crisis? Do you remember paying $4.00 a gallon for gas recently?