Re: Straight Eight Compression Distance

Posted by Eric Boyle On 2007/12/23 0:28:50

That's what I thought, between the 288 and the 327 using the same pistons. Which would mean that they made up the difference in stroke by shortening/lengthening the rods, or changing the deck height. The 288 has a 3.75 stroke, and the 327 has a 4.25 stroke. A 7.6875" rod in the 327 + 2.125" for the piston + 2.125" (1/2 the stroke)= 11.9375", which is the approximate deck height of a 327.

A 288, at 7.9375" rod, + 2.125" pin height, + 1.875" (1/2 the stroke)= 11.9375". Which means they have the same deck height. Now, change this up a little, put the 288 rod in the 327 engine, now you have: a 7.9375" rod, + a 2.125" (1/2 the stroke)= 10.0625", the total length of the 1/2 stroke and the rod. Now, take the 11.9375" deck height - the 10.0625", and you come up with: 1.875", which is now the new pin height.

OR

You could have just done this: asked me! All this holds true if the deck heights are the same. I won't even go into the 356 as it's a different breed of engine, and from what I can tell from repair manuals, the rods from the later engines won't fit into the 356.

Now, the point of this exercise is twofold: #1-To obtain a shorter pin height piston that is more easily available in custom forged pistons than the stock piston pin height. 2.125" is a tall piston in a 3.5" bore configuration.

And #2-To increase the rod/stroke ratio. Everyone knows that a longer rod makes more torque, since the piston stays longer at the top and bottom of the stroke. Now, in my particular application, this will be most beneficial. As long as, the longer rods don't meet the sides of the block or the camshaft. Hence the need for a 327 9 main engine over the 356 or even the 359. Shorter stroke on the 327, plus the longer rods of the 288, and I should be able to make more torque at lower revs than with the stock rods. Plus, I get the added benefit of less friction on the cylinder walls with the shorter piston.

Have I lost it? Probably!!