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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Now we come to the rods. This is a critical aspect of the build. The problem with many rods is that they require a lot of block cutting to give the bolt shoulder clearance with both the block and the camshaft. In addition to this, the bolt head also runs into the pan rail so that also needs to be cut for clearance. The Scat stroker rod aggressively addresses these issues. By utilizing top-grade material for the rods, minimizing bolt thread engagement to the shortest length possible without compromising strength and a compact design on the cap’s bolt platform Scat has reduced the rod’s mass in the areas most critical to a stroker. The result is that the rod actually has as much as 0.060-inch clearance with a stock base circle cam.

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Now you may ask what’s the deal here? It takes next to nothing in the way of effort to order a reduced base circle cam. As Walters will tell you in short order a lot of effort went into the utilization of as big a base circle cam as possible in his Pro Stockers. The reason is that the bigger base circle cams allow for more lifter acceleration before roller lifter side thrust limitations are reached. Also, preserving as large a base circle as possible allows for a more aggressive profile (a key element in power production) while still retaining streetable reliability. So, in a secondary way, the Scat rod combined with the 3.875-inch stroke is worth power because it allows a more aggressive cam to be used. The cam is a subject discussed in more detail below, but for now it should be clear that in addition to costing a lot less than a 408 stroker this 396 is looking good in the way of output potential.

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Compared to a stock mill, this engine has a lot of cubes to fill. Without exceptionally good heads those cubes will be starved of air and be underutilized. Here, Walters favors heads from AFR and Dart. For this build the heads are Dart 200cc runner castings hand-ported by a highly experienced and championship-winning head porter friend of Walters’. The intake runners started at an average of 197 cc and, when finished, at 208 cc so not much came out of them. The key here was flow from an efficient port and not a big port, that way the port velocity was higher. This has the benefit of delivering better low-speed output as well as enhancing the top end. Also, a high-efficiency intake valve seat was used that delivers low and mid range flow figures more akin to a 2.150-inch intake valve rather than the 2.08-inch used. Conceptually, the exhaust ports were the same as the intakes in as much as they were modified for maximum flow from a highly efficient shape rather than just a big port. Velocity probing showed that the velocity distribution across the port was far more even than most heads we have seen. This is yet another factor toward good low-speed manners. In short, these heads had more than enough flow to easily exceed 600 hp from a race 350 so it would be interesting to see what our 396cam’d more for the street and with just a 10.5:1 CRwould do.

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