Plymouth Roadrunner Torque Monster - Mopar Project Car

Indy Cylinder Head's recipe for reliable street performance delivers a broad powerband and 700 lb-ft of torque.

Grunt, Oomph, Twist. That's real power.

Power is what Mopars are known for. At the root of that power, the key to wheel-lifting launches and asphalt-rippling burnouts is torque.

Torque is also what defined '60s muscle cars. While today's four-valve, DOHC, fuel-injected vehicles offer performance, you don't hear much about torque-nor do you feel it. Today's high-revving, light-switch-for-power engines are super-efficient, clean burning, and high-revving. But they lack pin-you-in-your-seat power that forces you hang on when the pedal hits the floor. Heck, in some cases, a torque monster doesn't require even moderate accelerator pedal travel.

Perhaps that is why when Holley chose to build ten project cars-one from each decade of the company's existence-there was no question that the automotive selection for the decade beginning in 1960 would be a big-block Mopar. Holley Performance Products and its brands including Lunati, Hooker, Earls, Holley Superchargers, Weiand, and Nitrous Oxide Systems all have an affinity with large cubic inch, V8 muscle. The choice to go with a Mopar for a decade as important as the '60s is significant commentary regarding whose muscle cars made the most power consistently.

Torque is the back-to-basics commentary-but how would one add a twist of today's trends. When Holley approached us about their Project Roadrunner, they asked who we thought should engineer the Mopar-specific powertrain combination. Certainly, the answers could range from a crate Wedge or Hemi from Mopar Performance Parts, but that might reduce the potential content of Holley brands in the engine assembly. With the goal of exhibiting Holley's brands, we suggested that Indy Cylinder Head be the engine builder. With their loyalty to the Mopar community-displayed in their long list of products made specifically for Mopars-as well as their far-reaching reputation, we knew that Indy would be the place to go.

Holley agreed-in fact they had already come to the same conclusion prior to our suggestion. Holley would look to Indy Cylinder Head for the gospel according to Mopar big-block power. In the early discussions with Ken Lazzeri of Indy Cylinder Head, it was apparent that there were several options-maybe a mid 400ci low-block stroker or perhaps a huge displacement 440-based RB. The intended use is what helped to make the final decision of which displacement big-block Mopar to build.

The Holley Performance Products Project Roadrunner would be a street car. Sure, it might do a quarter-mile once in a while, but primary use would be cruising-even long distance Hot Rod-style Power Touring. This Roadrunner would be four-speed shifted backed up by the stoutest Hemi A833 possible, yet produce enough torque that you could basically leave it in Third all the time.

Lazzeri told us, "We have built many 500ci pump gas engines and they were capable of 600 to 610 lb-ft of torque and nearly equal horsepower-in street compression. Additional displacement was the key to building a torque monster." Ken also knew that a bit more displacement may pull down the horsepower figure, but the torque would rise exponentially. "When you try to create a torque monster on purpose, the equation is fairly simple-moderately high velocity heads and a relatively small camshaft. You sacrifice peak horsepower."

Sacrifice horsepower? "Heresy," you say. Ken continues, "The reality is that building high-torque engines puts horsepower on hold. Our goal was torque first." Remember, horsepower is a function of torque. The polar moment of inertia happens sooner when the fulcrum favors the power source rather than the object to be moved.