396ci Small-Block - Tech

This popular big-block displacement comes in a new flavor!

David Vizard Jan 10, 2011 0 Comment(s)
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So where do we stand if the stroke is limited to 3.875 instead of 4.00 inches? Here is Walters’ take on the situation. First, using a 3.875-inch stroke instead of 4.00 inches with the typical 0.030-inch overbore results in 12 less inches: 396 instead of 408. But this shorter stroke and a slightly better rod-to-stroke ratio cuts down on side thrust and means less piston-to-wall friction. The result is that we don’t lose the benefit of 12 cubes compared to the 408 but something more along the lines of 8 cubes. Also at this displacement, top end output is dictated more by the cylinder heads than the displacement. At the end of the day the 396 should make as good a top end as a 408 and have a torque output equivalent of about 8 cubes less than a 408. All this comes with greater reliability and a lot less cash investment in the block.

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For cranks and rods Walters works almost exclusively with Scat and not unexpectedly they have some major contributions toward the justification of the 396 as a top choice for a stroker 350 deal. Because of their extensive experience in the stroker business Scat continually strives to design cranks and rods that allow the most to be achieved within the confines of a 350 crankcase. Scat’s efforts in this department played right into Walters’ hands as far as being able to build a 396 for only the additional cost of a forged crank instead of the usual 383 cast-steel crank. Scat’s latest offerings allow a 3.875-inch stroke rotating assembly to just about fit where a typical 3.75-inch stroke normally fits. The bottom line here is that if Walters is right, we should get a 396 that delivers as good or maybe a shade better in terms of peak power while only sacrificing torque consistent with about 8, not 12, cubes less. All this sounds good in theory, so let’s see how it works out in practice.

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The Block

To build big power numbers, it requires a stout block, so the starting point for a TWPE 396 is eliminating the less-than-desirable candidates by means of sonic testing. After a block has been selected it goes through all the procedures one would expect of a top-dollar race engine. This includes cutting the clearances for the rods and the subsequent 100-psi pressure testing.

Rotating Assembly

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The heart of this 396 stroker build is the Scat 3.875-inch crank. There is considerably more to the design of a crank than you may at first suspect. For strokes as long as or longer than that of the 400 small-block (3.75-inch) an external balance is the norm because of a lack of crankcase space for the counterweights. For what it’s worth external balancing is a Band-Aid fix as it causes an increase in crank snout flexing at high rpm. This may not be an issue for a grannymobile but it can be for a high-rpm race unit. Most small-block Chevy cranks have insufficient counterbalance mass for the two inner cylinders. Being aware of this, Scat designed a crank that has the potential to be internally balanced to achieve the best possible solution. To make the counterbalance more effective, hollow rod journals are employed.

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Although designed to be internally balanced the Scat 396 crank still needs to be teamed with appropriate rods and pistons. First the pistons, not only must they be tough, have a top-notch ring package, but also be light to fall in line with an internal balance job. Here Walters uses pistons from SRP equipped with Total Seal rings. Why Total Seal? There are quality rings out there that cost less than the gapless Total Seal design but Walters’ answer here is: The dyno tells me I should use them!

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