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Original Message
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| A Ford 427 is 426 CID plus change |
| By Dave Shoe - 11/17/2000 6:41:19 PM; IP 12.2.11.131 |
The base 427 bore was 4.2330+-.0002 (grade 1 bore diameter) with 3.784 stroke. This gives it a 426.017" displacement. A grade 2 bore is .0004" larger. Grade 3 another .0004" larger and these first three all used one piston grade ('color code red' piston). The next three bore grades, 4, 5, 6, used the 'color code blue' piston. There were two more grades, called A and B, which were got a third sized piston known as the '.003" oversize' piston. It wasn't exactly .003" over, but more accurately .0024" over the base piston. A 427 with all grade "B" cylinders (4.2358+-.0002") had a displacement of 426.581 CID.
Note that in 1966 the piston diameter spec for the 427 was 4.2287+-.0003" (red), 4.2299+-.0003" (blue), and 4.2311+-.0003" (.003" oversize). I believe the piston diameter spec would have sometimes changed depending on year or application, but the cylinder diameter spec would have always been the same.
Note that there were probably no blocks which had only grade 1 or only grade B cylinder bores. It's tough to keep all bores identical on a production line because the cutting stones wear so rapidly (pistons are made with hard tooling, and are probably much easier to control the size of) and all 8 bores are cut with 8 different cutting tools. Each cylinder was typically different from the neighboring cylinder. The large characters painted in the galley of the new blocks indicated the cylinder bore grade, and thus told the production line assemblers which piston to put into the bore.
Ford engineers, no doubt, picked the bore and stroke so that it would be as close to 7.0 liters (427.166 CID) as possible without being so close that some engines would end up being over the class limit due to machining tolerances.
The 428FE was 4.1302 X 3.984 (grade 1 cylinder) which is 427.013 CID, keeping it legal for 7-liter racing. A Grade B cylindered 428 weighed in at 427.592 CID, so I don't quite understand how this motor squeaked in under the limit. Additionally, a 428 bore is spec'd at 68 degrees F, so even a grade 1 cylindered block block would teeter right over the 7-liter wall due to thermal expansion when outdoor temperature reached 96 degrees. Does this mean the 428 was not allowed to race on hot days???
I also don't know why the 427 had a slightly longer stroke than the 390 (at 3.781"), but this is a fairly consistent spec in the manuals I've run across.
Final note: I generally round pi to eight decimal places in my calculations.
As usual, my facts are mixed with rumor,
Shoe.
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