Timing is Everything:

Distributor Tuning for Power and Economy (Part 2)

Text and Photos by Chris Holley

The two test Darts, a ’67 Dart (foreground) and a ’75 Dart (background). The motivation for both Darts were stock 225 slant six engines. The pre-distributor modification testing resulted in a peak of 119 lb/ft of torque at 2800 rpm and the horsepower was 76 hp at 3600 rpm for the ’67 Dart. The ’75 Dart performed slightly better with the slant six’s output climbing to a peak of 127 lb/ft of torque at 2700 rpm and the horsepower was 78 hp at 3600 rpm.

As an introduction to part two of the distributor modifications testing series, a little refresher of what was covered in part one with the two vintage Dodge Darts is necessary. The objective of this two-part series was to attempt to increase the power output of the Darts (one is a ’67 Dart and the other is a ’75 Dart, both sporting 225 slant sixes), while increasing the fuel economy of the ’75 Dart. In part one of Timing is Everything: Distributor Tuning for Power and Economy, the harmonic balancer alignment marks were verified for top dead center (TDC) on both engines. The speedometer gauge on the ’75 Dart was tested for accuracy on the Pennsylvania College of Technology’s Mustang chassis dynamometer. To reduce the variations between the ignition systems, the ’67 Dart’s points ignition was replaced with an electronic ignition very similar to the ’75 Dart. A baseline of rear wheel torque and horsepower was established with three runs ranging of 2600 rpm to 3800 rpm for each Dart. The ’67 Dart’s slant put down a peak of 119 lb/ft of torque at 2800 rpm and the horsepower was 76 hp at 3600 rpm. The average numbers through the rpm range were 113 lb/ft of torque and 72 horsepower. The ’75 Dart was a little more impressive (but not too much) with the slant six output climbing to a peak of 127 lb/ft of torque at 2700 rpm and the horsepower was 78 hp at 3600 rpm. The average numbers through the rpm range were 121 lb/ft of torque and 73 horsepower. With the overview concluded, the newly modified distributors were now ready to play a substantial part in the increase (hopefully) of the performance numbers of each slant six.