What do you know; it's that time already. Just like we promised, here's part two of the Vrbancic Brothers Racing pump-gas blown 383 stroker. Oh yeah, this time we brought some friends along. What friends you ask? How about numeric friends? The dyno results are in. We're pretty sure you won't be disappointed.
Before we get started, lets have a little review. For those of you not familiar with Part I, the goal for this engine was simple. Get 700 horses out of a big-inch small-block with a supercharger while still having a streetable motor. What's the definition of streetable? In this case something that would idle at a stoplight, and could be filled up with 91-octane at the gas station. Also if you're wondering about the compression, it's 8.8:1. The build was based on a World Products Motown race-prepped 350 block that is built to handle the high-combustion pressures of a supercharger. The supercharger chosen to complement the block was a D1-SC centrifugal supercharger from ATI Procharger. Rounding out the motor is Holley Systemax parts, including a matched set of intake manifold, heads, and valvetrain along with an entire rotating assembly. Various parts from other performance companies topped it all off.
Once the motor was finished, it was time to see what she was made of. The 383 took a trip (of about 15 feet) to the Vrbancic Brothers Racing state-of-the-art DTS dyno. Arco 91-octane gas was the choice of fuel for the application, based on the fact it's the cheapest high-octane gas in the So Cal market. The 383 was placed on the dyno with the Carb Shop prepped Holley CF 750 carb jetted with 74s in the primaries and 86s in the secondaries. For the initial dyno run the timing was set at 28 degrees. The first pull posted more than respectable numbers. The 383 cranked out 685.9 hp and 600.3 ft-lb of torque at 6,000 rpm with 11 pounds of boost. The motor even pushed out 462.8 ft-lb of torque at 2,800 rpm! Can anyone say burnout? Any streetcar would light 'em up with that kind of power; however, the goal was 700 hp.
For the second run, Bob Vrbancic knew some changes were necessary to climb into the 700 range. Vrbancic Racing decided to change the primaries from 74s to 72s and switch to 84s, instead of 86s, in the back. Also to help aid in the quest for 700 hp, Red Line 50WT synthetic race oil was added to the mix. The timing was also changed to 34 degrees. Included in the MSD ignition is a boost retard control. The retard control allows users to instantly retard the boost one to three degrees. Bob decided to retard the boost one degree, which calculates out to 1-degree retard per pound of boost.
For the second pull Vrbancic decided to rev the motor higher. This time the 383 would be revved to 6,100 rpm instead of 6,000 rpm. As it turned out the changes made were just what the motor needed. The second pull pumped out 35 more horsepower and 20 more ft-lb of torque. That's right the motor jumped from 685.9 hp to 720.3 hp and the torque went from 600.3 to 620.1 ft-lb. Not bad! The boost also increased to 13.2 pounds. I guess I'd put that in my car, but only if I had to!