There’s No Replacement for Displacement

The Real Story Behind the First GTO’s Engine Size

By Christopher R. Phillip

To understand how Pontiac successfully put a 389ci engine—normally only available in full-size cars—into the intermediate size LeMans, you’ll need a calculator … but don’t worry, the math is easy.

General Motors had a policy not to exceed 1 cubic inch per 10 pounds of vehicle weight, with the only exception being the Chevrolet Corvette.

Depending on which version of the 1964 GTO produced, factory-shipping weight came in at 3106-3360 lbs.

Now do the math: 3106(lbs.)/10(lbs.)=310 (cubic inches). Pontiac’s engine with the closest cubic inch displacement was the 326.

By GM rules, there was no way Pontiac could officially put a 389 into the LeMans.

So how did Pontiac do it? Smart-thinking John Z. DeLorean followed GM’s rule but not its intent. He knew that the policy applied to car models—such as a Tempest or Catalina—but not to option packages on a model.

He cleverly made the GTO an option package on the LeMans, bypassed the GM rule, and invented America’s very first muscle car.

Now it’s your turn. Go to to win a prime example from the GTO’s history. Dream Giveaway Garage’s 1965 GTO is fully restored and autographed by DeLorean’s Assistant Chief Engineer Bill Collins.