A relatively narrow lobe separation is key for brutal, hard-hitting mid-range torque, while plenty of overlap and extra exhaust duration is the usual call for making an engine hang on into the higher revs. We found both of these qualities in COMP's new Thumpr line of camshafts. A COMP Big Mutha Thumpr (BMT) PN 11-602-8 stick got the nod, which is an off-the-shelf grind featuring 243/257 degrees of duration at .050 inch, .570/.554-inch lift, and a tight 107-degree lobe separation angle. To make the most of the camshaft, a reliable valvetrain was assembled with components from COMP, including COMP's retrofit hydraulic roller lifters to fit out a Mark IV block, COMP Hi-Tech 3/8-inch pushrods, and aluminum 1.7:1 roller rockers. A final trick to really make the big engine spin to its full potential was to specify COMP's Beehive valvesprings on those RHS cylinder heads. RHS obliged this request and now features this setup with a dedicated part number (11001-05).
 An oil ring support rail is...  An oil ring support rail is used to retain the oil ring when the pin breaches its groove. A small dimple on the rail lies face-down in the slot created by the pin hole, keeping the rail in position. |  A key part of the Howitzer's...  A key part of the Howitzer's power-producing scheme was a set of high-flowing aluminum heads. For the rpm range we intended, these RHS 320cc cylinder heads proved to be ideal. |  With a hydraulic roller cam,...  With a hydraulic roller cam, maintaining high-rpm valve control can be a challenge. We ordered our heads fitted with COMP's beehive springs, which can significantly improve valvetrain control and stability. RHS now offers this combination as an option on its big-block Chevy head package. |
With this, we had our basic combination, and the promise of mega torque. We took the load of parts-including oil system components from Melling, all-new tin from AAMidwest, an MSD HEI setup, and ARP bolts to screw it all together-to Andy Mitchell's Outlaw Racing Engines (Upland, CA). Andy oversaw the assembly, and measured everything to blueprint specs, while Hunkins and Outlaw part-timer Tim Martindale, helped work the nuts and bolts between shooting photographs and cooking ribeyes on the grill. What emerged was a hot-looking 496 that will fit under the stock Chevelle hood, chomping at the chance to prove its stuff come dyno day.
It wasn't long before the big-block was hauled to Westech Performance Group and bolted on a SuperFlow 902 dyno to validate the combination. Dyno master Steve Brul performed the preliminary checks of base carb and ignition settings, and the rat fired with authority. With a hydraulic roller combination, the cam break-in drama of a flat tappet is completely sidestepped, but the engine was run through a programmed load cycle to help seat the rings and prepare for the action to come. With a compression ratio of 10.2:1, there was no need to feed the Mighty Demon carb anything but standard-issue pump premium fuel. A few static checks under load helped sort the jetting.
With the formalities out of the way, it was time to let it rip. As the numbers rolled in, the big-block showed its true character. Want to propel a heavy street machine with explosive power? The Howitzer was revealing itself to be the ideal weapon, with a numbing 600 lb-ft churning right from 3,200 rpm, climbing to a peak of 635 lb-ft at 3,800 rpm. Wow, that's a lot of torque, and it comes in right now! We've seen some engines build a lot of low-end torque, only to give up low in the rpm range with no big horsepower bang up top. This isn't the case with The Howitzer. Our big Chevy just kept coming, making power right up to 6,000 rpm, and beyond. Torque recorded over 600 lb-ft right up to 5,300 rpm, and power held strong to the top, recording a peak of 626 hp, coming in at 5,900 rpm. Even past peak, the engine only slowly came off the crest, pulling easily higher. This is an engine that will hit like a cannon out of the hole, and keep pulling like an artillery piece barreling headlong to a shift point just over 6,000 rpm. Our Howitzer is one engine that's earned its name.
 We brought the RHS heads to...  We brought the RHS heads to Westech Performance Group where they were tested on a SuperFlow 600 bench to evaluate flow. The 320cc intake port delivered an impressive 328/350-cfm peak flow on the intake ports, and 276 cfm on the exhaust. |  Big Mutha Thumpr:When COMP's...  Big Mutha Thumpr:When COMP's new Thumpr hydraulic roller cams first came out, many thought it was just a noise cam, but we knew otherwise. With a long exhaust duration and a narrow 107-degree LSA, we saw a recipe for big street power. Retrofit hydraulic lifters are needed for engines not originally equipped with a hydraulic roller cam, so we also ordered the retrofit lifter kit for our BBC. Thumpr cams are available for small- and big-block Chevy, Ford Windsor, and small-block Chrysler. Three unique grinds are available in each engine family-we chose the biggest for our Rat Chevy (299/319 advertised duration, 243/257 at .050, .570/.554-inch lift, 107 LSA). |  File-fitting the rings allows...  File-fitting the rings allows a builder to control the end gaps for minimal compression leakage. Outlaw uses go/no-go feeler gauges to quickly and accurately determine the end gap. We were shooting for a .020-inch gap for the top compression ring, .022 inch for the second, and anywhere between .016 and .028 inch on the oil rings. |