The 420 Mega Blower was equipped with a pair of blower-specific 750 Holley carbs and dual-
We made full use of the valve relief in the Probe Racing forged pistons by replacing the wimpy hydraulic flat-tappet cam run previously in the 461 with a custom hydraulic roller cam. Comp Cams supplied the Xtreme Energy hydraulic roller profile, which offered a 236/242 duration split at .050 along with over .600 lift. The intake featured a tad more lift, checking in at .646, while the exhaust was down only slightly to .623. The cam featured a wide 114 lobe separation angle, helping produce a broad power band and minimizing overlap. The custom Comp hydraulic roller cam was run with a set of Comp hydraulic roller lifters, hardened pushrods and a double roller timing chain.
The use of the hydraulic roller cam required a cam button to control the cam movement. Unlike hydraulic flat-tappet cams, roller profiles do not have angled lobes to keep the cam from walking forward. It was necessary to set the cam button lash using the shims provided in the two-piece timing cover kit. The two-piece aluminum timing cover made the necessary adjustments to the cam button much easier, not to mention kicking the cool factor up a couple of notches.
On the dyno, the blown 489 pumped out 728 hp and 690 lb-ft of torque at just 4.3 psi of bo
With more cam and cubes, we turned our attention to the cylinder heads. Though we had good luck with the factory 049 heads (ported by Joel Marsh of Competition Heads in Fullerton, California), we knew the aftermarket had much to offer in the way of performance headgear. We contacted Canfield cylinder heads, and they shipped out a set of their 310cc aluminum heads. Right away the Canfield heads were a step up from the 049 heads, as the aluminum heads offered a dramatic weight savings (ever had to lug a set of big-block Chevy iron heads?) along with a reduction in detonation potential thanks to the superior heat dissipation of aluminum.
The final improvement involved the flow rate of the Canfield heads. Though we installed the heads out-of-the-box with no porting, the Canfield 310s easily out-flowed the ported 049 heads, by as much as 40-50 cfm per runner. The Canfield heads were equipped with a 2.25/1.88 stainless steel valve combination and treated to a performance three-angle valve job. The headwork was performed by Dougan's Machine shop in Mira Loma, California. The Canfield heads were completed with dual valve springs, retainers and spring seats, all from the Comp Cams catalog.
Each pulley combination was run on the dyno, with predictable results. As we increased blo
The only thing missing from the 489 stroker long-block was an intake, carb and ignition. We installed 2-inch Hooker Super Comp headers (for a Chevelle chassis) used previously for dyno testing, but the Canfield heads were topped with an Edelbrock Performer RPM Air Gap intake. We chose the dual-plane intake for its superior torque production. Sure, the racy single-plane Victor Jr. or Super Victor will make more peak power, but we were interested in having a broad torque curve capable of offering impressive acceleration and even improved fuel consumption over a single plane. For street use, nothing beats a dual-plane intake for maximizing torque production.
The Air Gap intake was topped off with a Holley 950 HP carburetor to ensure plenty of air and fuel for our thirsty stroker. Additional mods included a TCI Rattler balancer (external 454 balance), an MSD billet distributor (and wires) and a set of 1.7-ratio roller rockers. The motor was run on the dyno with the Hooker headers feeding a 3.5-inch exhaust equipped with mufflers.
After running the 489 in normally aspirated form, we yanked the RPM Air Gap and 950 HP car
After filling the pan with Lucas oil and a proper break in procedure, we were initially rewarded with 545 hp and 571 lb-ft of torque. After playing with the ignition timing, the carb jetting and finally installing a 1-inch carb spacer, we managed to coax 577 hp and 592 lb-ft of torque out of the normally aspirated 489 stroker. Even more impressive was the fact that the power came on Union 76 unleaded pump gas, thanks to a compression ratio of just 8.25:1.
Satisfied with the results of our normally aspirated 489, we quickly got to work and yanked the Performer RPM Air Gap intake and 950 HP carb and replaced them with the 420 Mega Blower and dual 750 (blower specific) Holley carbs. We reduced the ignition timing from 35 to 31 and proceeded to make some serious power-after all, the low-compression stroker was built with supercharging in mind.
Not surprisingly, adding the Holley 420 Mega Blower made a dramatic difference in the power output of the 489. Running a 56-tooth blower pulley and a 50-tooth crank pulley produced a blower drive ratio of roughly 11 percent under-driven (meaning the blower was spinning only 89 percent of the engine speed). The result of the 11 percent under-driven Mega Blower was an increase in peak power from 577 hp to 728 hp. The drive ratio produced a peak boost pressure of just 4.3 psi, with most of the run registering under 4 psi.