BOB's engine
Larry's Track Pro 422ci Small-Block
Building a small-block on a $6,500 diet to make big-block power means you'd better come to the party with a decent amount of displacement. With this lofty goal, I penciled out a plan to gain 422 ci from a production 400 small-block with a Scat 3.875-inch-stroke crank, Scat 6.00-inch rods, and off-the-shelf Ross forged pistons. Through the help of Jim Escamilla of Larry's Performance, we uncovered a useable 400 small-block core. This block was a 3951509 two-bolt item, originally installed in a '79 Chevy delivery truck, and it only required general machine work and a 0.040-inch bore job to be squared-to-the-world and ready for assembly. If a modest budget and shrinking calendar were not the limiting factors, I would have opted for even more cubic inches.
The central goal for this competition was to make as much big-end power as possible and run it on high-test (91-octane) pump gas. This meant it would not be a well-mannered street-performance motor with a big, broad power curve. Instead this would largely be a single-purpose powerhouse, a welcome breaking away from decorous convention.
With these parameters drawn, I selected a series of performance parts designed to make lots of power above 4,500 rpm. I considered several cylinder heads for the test that would flow a large amount of air, were easily obtainable, and came at a budget price. Next I wanted a cam with off-the-map lift numbers and lots of duration. On the intake manifold side, the engine needed to draw hordes of air and fuel quickly into the engine. Because the price of carburetion wasn't part of the $6,500 budget, I decided to mount a pair of 750-cfm double-pumper four-barrels to a tunnel-ram intake manifold. Again, this engine's single purpose was to make as much upper-rpm power as possible. On a street- or weekend-performance car, this engine would be a hassle to drive, sort of like using a racehorse to pull a cart.
By the time I had the engine completed and ran a tally, the numbers fell just dollars below our $6,500 cap. Had there been a little more time, I would have liked to spend some time on a flow bench improving the cylinder head's flow capabilities, and with the big cam it would have been possible to run more compression in this engine on the dyno. As with any engine build, though, you walk away with a to-do list for next time. What's especially noteworthy with this 422 is that after we finished the dyno pulls, the little powerhouse outperformed its competition with 1.36 hp per cubic inch. All in all, I think I would have traded that triumph for the higher horsepower mark.
With a solid roller camshaft...
With a solid roller camshaft producing 0.686 inch maximum lift, we ran into some clearance issues during assembly between the bottoms of the rocker arms and the retainers. To achieve the needed clearance, we carefully ground the bottom sides of each rocker (arrows), without making any sharp edges.
Our Comp Cams valvesprings...
Our Comp Cams valvesprings produced 300 pounds on the seat at 1.900-inch installed height. We also used Pro Comp 1.52:1 roller rockers, 10-degree locks, and 8.10-inch pushrods. The total of these components allowed each valve to reach maximum lift without any clearance issues.
To achieve lots of high-rpm...
To achieve lots of high-rpm power, we added an Edelbrock Victor Ram tunnel-ram intake manifold. This is largely designed for high-rpm operation and would not work well in a street-driven vehicle where low-speed torque (below 4,500 rpm) is used to provide good acceleration.