In terms of heavy ordinance, a Howitzer is a big gun designed to do damage by propelling a large projectile with a seriously unruly velocity. The aim of our big-block Chevrolet build is to achieve a very similar goal, but with Hunkins' '68 Chevelle playing the part of the projectile. Moving a big street machine in heavy-hitting fashion is best done with a heavy-hitting powerplant. You can read that as big on cubes, big on torque, and, of course, big on power. Those three characteristics pretty much define the objectives of our Howitzer 496 stroker. Our goal was to build the engine using quality parts on a realistic working man's budget, which may be a little more than what an odd-jobber or alley-dwelling wino can spend, but a lot less than many cost-no-object builds we've seen.
The 496 big-block Chevy stroker has become a popular combination, based on a 454 block bored .060 inch, and fitted with an aftermarket crankshaft with an increase in stroke to 4.250 inch from the factory 4.00 inch. Frankly, when the engine is receiving a full rebuild, that quarter-inch of stroke comes mighty cheap. Our Scat rotating assembly retails at $1,268 when sourced from Survival Motorsports, and includes a cast-steel crank, I-beam rods, SRP domed pistons, JE rings, and Clevite bearings. Not a bad deal for most of the bottom-end hard parts, and a real bargain considering the extra 36 cubes bagged in the deal. When considering to build a fresh 454 with new rods and pistons, the ante is just not that much more to step up to a full 496 rotating assembly and let those extra cubes work.
 "I have a hard time sleeping...  "I have a hard time sleeping at night, thinking about this 496 in the Chevelle. This thing is going to scare the neighborhood kids silly."-Johnny Hunkins |  Although it isn't a forging,...  Although it isn't a forging, the Scat cast-steel crank is substantially stronger than a production cast crank, and has been proven in performance street and race applications. Notice the filet radius at the journals, net-shape counterweights, and nicely detailed oil holes. The Scat assembly is close enough in balance to assemble at home as-is, but we had the guys at B&T Performance (Pomona, CA) balance ours to our specific flexplate and balancer. |  Viewed side by side, it's...  Viewed side by side, it's easy to see the extra beef in the new Scat I-beam rod, compared to a stock rod (left). Harder to see is the advantage in materials, with the Scat rod's 4130 steel having significantly more strength than the 10-series OEM carbon steel. |
Of course, more cubes naturally have a heartier appetite for air, so taking advantage of the displacement increase means a healthy set of cylinder heads. We knew that we wanted a set of aftermarket aluminum heads. Though there are some good iron heads on the market, the weight advantage of aluminum is a definite plus when considering the conspicuous heft of an all-iron big-block. Before jumping off the deep end, it pays to have a set objective in mind when shopping the virtually unlimited range of big-block Chevy cylinder heads. Our notion was to build a torquey pump-gas street piece, not an all-out drag engine. We would select a hydraulic roller cam for long-term durability and low maintenance. The cam selection, along with the moderate street bottom end, dictates a maximum reliable engine speed between 6,000 and 6,500 rpm-not 7,000-plus rpm. For this max rpm range, a moderate performance cylinder head would serve the engine's needs handily. We went with the Racing Head Service 320cc (intake runner) heads. At just over $1,800 (per pair, assembled), these heads are reasonably priced, and with over 350 cfm of max airflow on hand, we had more than enough air to make power in our street combination.
A stroker with nearly 500 ci will naturally produce torque in abundance, and torque would be key to effortlessly heaving the Street Sweeper Chevelle. We decided not to fight the natural tendency for torque, but instead sought to maximize it in the rest of our parts selection. To complement the cylinder heads, an Edelbrock Performer RPM Air Gap intake was selected. A two-plane with 180-degree runner separation and ample runner length will always have a torque advantage in the low- to mid-range compared to a single-plane. The Air Gap is about as good as it gets in terms of out-of-the-box flow from a two-plane, and the divorced runners maintain a cooler, more powerful fuel/air charge. Ensuring adequate air with fuel mixed in the proper proportion, we coupled the manifold to an 850 cfm Mighty Demon carb. Sure, a single-plane would likely bring in a higher peak horsepower number at the top of the rpm range, and many builders will make that trade. Our plan was to go for the fatter torque curve over a wider portion of the engine's operating range, and retain the stock flat hood in the deal.
Similarly, when it came time to select the camshaft, we had a few alternatives. A hydraulic roller has just too much going for it to pass it up in this type of application, particularly in a big stroker that doesn't need extreme rpm to make power. Few will argue the reliability advantage of a hydraulic roller in comparison to a solid roller or a flat-tappet design. While either of the alternative solids can provide the benefit of easier high-rpm potential, the beauty of a stroker is that you don't have to go there to reap its performance rewards. As with the rest of the combination, we were looking for a camshaft profile that would come on with strong torque, and yet pull without argument to the 6,000 rpm range.
 With a longer stroke, the...  With a longer stroke, the piston requires a shorter compression height, which is the distance from the center of the piston pin to the top of the piston. Note that the piston pin hole is machined right into the oil ring land. |  Scat's Budget 496 RecipeBig...  Scat's Budget 496 RecipeBig cubes can mean big power, and one of the best ways to easily get 496 inches is a matched stroker kit. Rather than a piecemeal set of parts, Scat's Series 9000 kit (around $1,300, mail order) has everything, including a cast steel crank, I-beam rods, forged SRP pistons, JE Pro Seal moly rings, and Clevite bearings. The balance factor was accurate to within 2 grams on our internally balanced kit. Basically all the guts you need in a pre-matched package, ready to assemble. |  The SRP pistons are manufactured...  The SRP pistons are manufactured by JE, and are a part of its affordable line of high-performance forged pistons. These PN 212157 pistons are made for Scat's .060-over stroker combination, with the correct compression height and skirt clearance. Ring grooves are 1/16-1/16-3/16, and the domes measure 18 cc, to give a final compression ratio of 10.2:1 when used with a 118cc combustion chamber. |