Chevy Stroker Kits Insight - Long-Armed Bandits

Small-Blocks Are The New Big-Blocks, And Big-Blocks Are Now Approaching 800 ci. How Big Do You Want To Go?

Stephen Kim Mar 1, 2009 0 Comment(s)

383/406
Some consider the venerable 383 antiquated, especially in light of the near-500ci potential of modern small-blocks, but the 383 is arguably the simplest stroker motor to build. Essentially a 0.030-over 350 with a 3.750-inch stroke, the 383's extra cubic inches are almost free when compared to the cost of retaining a stock 3.480-inch stroke. Gone are the days of digging up a 400 crank out of the junkyard and grinding down the mains to fit inside a 350 block. The 3.750-inch stroke small-block Chevy crank, whether cast or forged, is one of the most popular aftermarket cranks ever produced. Furthermore, the relatively short stroke allows fitment of rods up to 6.125 inches while still retaining 1.000-inch of compression height with a standard 9.000-inch deck height. "The rod bolts will hit the cam whenever duration exceeds about 220 degrees at 0.050 lift, but a small base-circle cam eliminates that problem," explains Judson Massingill of the School of Automotive Machinists. "Other than that, when using an aftermarket oil pan, the only other clearancing required is some minor grinding at the bottom of the cylinders when using a factory block."

If you manage to luck out amongst the dwindling supply of production 400 blocks or have the means to ante up for an aftermarket piece, matching a 3.750-inch crank with a 4.155-inch bore nets 406 ci. The advantages of this arrangement are gloriously over-square dimensions and ease of assembly right on par with a 383. The large bore helps unshroud the valves and coax extra cfm out of the cylinder heads, while the short stroke reduces piston speed and friction.

396/408
Adding an extra 0.125-inch of stroke to the ubiquitous 383 yields a total of 396 ci, and adding another 0.125-inch of stroke on top of that (4.000 inches total) results in 408 cubes. Realistically, these two displacement combinations are as large as you can go with a stock 350 block due to cylinder wall thickness and internal clearance issues. While some intrepid enthusiasts have successfully bored 350 blocks as large as 0.060 over, few will sonic-check well at that bore size, and overheating and block integrity can become issues even if there is sufficient cylinder wall thickness. In other words, the six bonus cubes you'd stand to gain by punching a 396/408 another 0.030 over aren't worth it.

Perhaps the biggest drawback of building a 396 or a 408 is the amount of additional clearancing required. "A 3.750-inch crank fits in a production block beautifully, but a 3.8750- or a 4.000-inch crank is a real pain to work with," says Judson Massingill from the School of Automotive Machinists. "When grinding the block to clear the rods, it's very easy to hit water." Moreover, compared to a 383, the longer stroke pushes the wrist pin higher up in the piston for any given rod length and results in a less favorable rod-to-stroke ratio. That said, if you're willing to put some extra effort into your stroker build, the 396 and 408 represent the ultimate in production-block-based power potential. In theory, the additional cubic inches and stroke should pay dividends in torque production.

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