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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There are four factors that dictate whether or not a valvetrain can be considered successful. These are reliability, valve event timing, valve lift, and, of course, cost. The valvetrain for our 396 was a very conscientiously spec’d setup centered around what, until recently, COMP Cams called their Busch profiles. These profiles are fairly aggressive to make really good power yet, when accompanied by appropriate valvetrain parts, pack the reliability to be streetable. Part of this reliability equation is the fact that the Scat rod will allow the use of a stock base circle cam. This not only cuts block-wearing side-loads but also improves dynamics. As for valve events, be aware that what works optimally for a 350 won’t even be within 25 hp of what’s needed for this 396. In this instance the cam profile used was a COMP 4875S on both intake and exhaust. These lobes have an advertised duration of 280/242 degrees at 0.050. The lobes are on a 106 LCA and, because of the strong low- and mid-lift flow of the Dart heads, the cam was timed in at 1 degree retarded instead of the more normal 4 degrees advanced. Just for the record, there is about 12 hp and an equal number of lb-ft difference between these two timing points.

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The COMP Cams Busch grind has a 0.381 lobe lift and to get the valve lift needed for outputs of 580 hp plus a 1.75:1 rocker ratio is needed. For the build here, a Crane set was used because Walters’ client for this engine already had a set with only an hour or two of use. The final valvetrain ingredient, and it’s of major importance, are the valvesprings. These are made by PAC for a third party, which is where Walters sources them. With only moderate spring forces on the seat and over the nose (net lift is 0.650) this spring will allow the valvetrain to turn a perfectly behaved 8,150 rpm with steel valves. This means it has plenty of margin for the 7,500 redline as our 396.

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Induction & Ignition

Just like everything else, there is nothing inconsequential about the induction system. The carb, which flows some 960 cfm, is specifically (available through TWPE) built for Walters by AED in Richmond. At 960 cfm it may be big but it services the engine as if it were a 750 down low and a 960 up topjust what is needed for a street/strip engine. The AED carb is mounted on a mildly prepped Edelbrock Super Victor, and for spark a 9,000-rpm capable Performance Distributors HEI with a custom curve was used.

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Dyno Time

The engine was loaded on the dyno and broken in. Next, it was given a post break-in service and made ready for some serious pulls. Nothing was very far off optimal on the first pull but at TWPE they don’t use the dyno to see how much horsepower the engine hasthey use it to see how much more they can find. After optimizing cam timing, fuel, and ignition this 396 pumped out 603 hp and 538 lb-ft of torqueall on pump gas.

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Now those are impressive numbers but let’s put that into prospective. First, a stroker is supposed to be about making torque. Sure, any stroker will make more torquethe question here really is did it make as much as it should have? A good torque output per cube for a streetable 10.5:1 small-block Chevy is 1.3 to 1.32 lb-ft per cube. That means to qualify as good our 396 needed to make 515 to 523 lb-ft. It made 538 lb-ft so on that basis it scored very well. As for horsepower, anything that is truly a street driver that makes 1.5 hp or better per cube can be rated as excellent. Our 396 made 1.522 hp per cube. Within the same cost, compression ratio, and cam duration bracket most 408s don’t crack the 1.5 hp per cube or 600 hp.

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For a build like this from TWPE figure $8,500 as entry level and about $9,800 for a replica of what’s presented here. (TWPE can also supply parts and subassemblies at very competitive prices.) So the price is good and that leaves us with only one question: What’s not to like? CHP

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