[PKRWUD]

There is a formula based on piston speed (and thus, stroke length), that determines an engines theoretical top speeds. It sheds some interesting light onto which engines would be better for high rpm modification. For example, all things being equal, a Chevy 327 has a max potential of 11,077 rpms, while a Pontiac 326's max is only 9600 rpms. Why is it that the Chevy has a max potential that is nearly 1500 rpm higher than that of another GM engine of virtually the same size? The stroke. The Pontiac 326 crank has a stroke that is 1/2" longer than the Chevy 327.

Using this formula and late 1980's parts, and classifying the engine as Stock (stock), Heavy Duty (stronger, factory parts), Built (mid budget aftermarket parts and machine work), and Race Only (the best parts and machine work available), the following are the theoretical limits for Ford engines:

Engine / Stroke / Stock / Heavy Duty / Built / Race Only

Small Block

289 ci / 2.870" / 7,317 rpms / 8,362 / 10,452 / 12,544

302 ci / 3.000" / 7,000 rpms / 8,000 / 10,000 / 12,000

351 ci / 3.500" / 6,000 rpms / 6,857 / 8,571 / 10,286

400 ci / 3.750" / 5,600 rpms / 6,400 / 8,000 / 9,600

Big Block

390 ci / 3.780" / 5,556 rpms / 6,349 / 7,937 / 9,524

427 ci / 3.780" / 5,556 rpms / 6,349 / 7,937 / 9,524

428 ci / 3.980" / 5,276 rpms / 6,030 / 7,538 / 9,045

429 ci / 3.590" / 5,850 rpms / 6,685 / 8,357 / 10,028

460 ci / 3.850" / 5,455 rpms / 6,234 / 7,792 / 9,351

Now, keep in mind that these numbers reflect the rpms at which the engine will hold together. For the actual max rpms, other factors need to be considered. This, however, is an excellent starting point for referencing an engines potential.

Take care,
-Chris