Ford Stroker Engine Sizing

Below is a quick outline of what displacements are produced using different bores and sizes. Keep in mind, the stock 5.0L Foxbody V8 engine is a 4.0" bore. When you 'stroke' an engine, you do not change the bore... well not really. A common misunderstanding is that a 347 using a different bore size from a 331. Actually, they both use a 4.030" bore (which is 0.030 larger than the stock 302 cu bore). Changing the cylinder bore size is done to clean up the bore after years of use. That is why you see engines that are speced as '302 bored 0.030 over'. What that means is the cylinder diameter was increased an additional 0.030" to remove imperfections during a rebuild. The stroke length of the engine is what differentiates between a 347, a 331 and the stock Foxbody 302. When you 'stroke' a motor, you increase the stroke length, and thus the displacement.

To calculate displacement, you use a very simple formula. Simply calculate the volume of each cylinder, and multiply by the number of cylinders. In a few neat lines, engine displacement formula is:

Engine Displacement Formula
(volume of cylinder) * (number of cylinders) = displacement
[pi*(bore/2)^2*stroke)] * (number of cylinders) = displacement

4.000" bore
3.00" stroke: 301.6 in3 (4.94L)
3.25" stroke: 326.7 in3 (5.35L)
3.40" stroke: 341.8 in3 (5.60L)

4.030" bore
3.00" stroke: 306.1 in3 (5.02L)
3.25" stroke: 331.6 in3 (5.43L)
3.40" stroke: 347.0 in3 (5.69L)

4.040" bore
3.00" stroke: 307.7 in3 (5.04L)
3.25" stroke: 333.3 in3 (5.46L)
3.40" stroke: 348.7 in3 (5.71L)

4.060" bore
3.00" stroke: 310.7 in3 (5.09L)
3.25" stroke: 336.6 in3 (5.52L)
3.40" stroke: 352.1 in3 (5.77L)

Stroking the stock 5.0L/302 cu engine is a great way to make more power. If you want to read more on how to make some power using a stroker, check out the Ford Engine Performance FAQ. It'll walk you through horsepower goals of 300rwhp, 400rwhp and 500rwhp either using a naturally aspirated stroker engine or forced induction.

-special thanks to kpgubert for submitting the stroker size table above.