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 uses a different (larger) bore size than a 331. In actuality, both 347 and 331 cubic inch engines 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. (A factory 302/5.0L block has a 4.0") 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.