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Big-Block Chevy Supercharger - Super Street Stroker

We Install A Holley 420 Mega Blower On A 489 And Mess With The Pulleys To Achieve 720 Hp.

By Richard Holdener

When it comes to forced induction, perhaps the best thing about owning a supercharged Chevy is the ability to literally dial in the desired amount of horsepower. If the motor is assembled properly using the right performance components, it is possible to adjust the boost pressure to achieve the desired output.

To illustrate the power gains offered by supercharging in general and then by pulley changes in particular, we decided to build a supercharged stroker and subject it to the rigors of the dyno. What follows is the build up of the dedicated big-block Chevy street stroker, along with the effects of adding a supercharger. After installing the Holley 420 Mega Blower, we took it upon ourselves to adjust the boost pressure by altering the blower drive ratio (via pulley changes).

After it was all said and done, we increased the power output of our already impressive normally aspirated stroker motor by a whopping 223 hp. What enthusiast wouldn't want an extra 223 hp?

The Holley/Weiand Roots blowers offer more than visual horsepower, as instantaneous boost provides immediate response and a wave of torque. The immediate boost response and impressive low-speed torque is one reason the Roots blowers continue to be so popular. When it comes to getting that big Chevelle, Camaro or even Impala moving in a big hurry, there is nothing like the feeling of a blown big-block. Taking the more-is-better route one step further, we decided that the only thing better than a big-block is an even bigger big-block. Combining additional cubic inches and forced induction can elevate your powerplant right to the top of the proverbial performance food chain.

Our test subject started out life as a 461 big-block. The 461 was originally equipped with a set of ported 049 oval-port heads, an emissions-legal Crane cam (203/212 duration) and an Edelbrock Performer 2-O intake. So equipped, the 461 produced 432 hp and 542 lb-ft of torque. For our needs, the 461 had two strikes against it in terms of performance as an optimum blower plant, namely the displacement and static compression. The displacement was too low while the compression was too high. Though the 461 offered decent low-speed torque production, our plan of attack was to build an even more impressive combination capable of bettering both the normally aspirated horsepower and torque production of the 461 while simultaneously allowing the combination to run effectively and effortlessly with our Holley 420 Mega Blower.

Given its mild state of tune, bettering the power output of the original 461 was not particularly difficult, as all we had to do was improve the efficiency of a few key components, namely the cylinder heads, cam and intake manifold. While adding free-flowing heads, a wilder cam and a high-rise intake manifold would surely improve the peak horsepower number, we also wanted to improve the torque peak-without sacrificing the impressive low-speed power already present.

Making life even more difficult was the fact that we had to achieve all this while dropping the compression down near 8.25:1 in preparation for boost. The game plan chosen was to combine the required low compression with an increase in displacement and efficiency. The additional cubic inches came from a stroker crank offered by Coast High Performance. The stock 4.0-inch (454) crank was ditched in favor of a cast 4.25-inch crank. Completing the stroker assembly was a set of forged I-beam rods and Probe Racing pistons. The forged pistons featured a single intake valve relief, as there is generally plenty of piston to (exhaust) valve clearance. The 4.25-inch crank was combined with the .030-over pistons to create a final displacement of 489 cubic inches.

By Richard Holdener
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