I had some really good Mopar friends that were super honest and had high end cars. They had a friend (they told me) that had bought a new '71 Duster, 340 4 speed, and tried for a year to get a 13 second pass. They tried different RPM launch's and shift points, they tried adjusting the metering rods and timing (only turning the factory adjustments, no altering), but never got their 13 second pass. They would go 14.0X's to 14-teens. But never got a 13.99.