Whats the best time for a factory stock duster 1/4 miles ??

This post is exactly right ....see post #50 Hersbird for a good summary....

Ronnie Sox in a factory equipped totally stock 1970 Duster 340 with a factory 4 speed and equipped with a 3.91 Sure Grip did a best of 13.98 ET at around 100 MPH in a Rapid Transit System test that was reported back in that timeframe.
Sox was one of the very best drag strip legends and he could shift a four speed like no one else.

These cars improved and responded well to basic bolt-on mods - cam, headers, intake, carb, ignition upgrade, torque converter upgrade with higher stall and maybe a valve body update....and a pinion snubber with larger good sticky rear tires.

But these mods were NOT part of a factory equipped car or factory option package.

One of the draws to buying the original 1970 Duster 340 was the low MSRP of $2,547 - well equipped. Also, Chrysler Plymouth provided a 5 year - 50,000 mile factory warranty on the drive train - the best in the auto industry at that time.
The Duster 340 was less expensive than the 1970 Dodge Dart Swinger 340 and it was marginally faster due to shorter wheelbase, and slightly lower weight.
Car Craft Magazine in May 1970 tested the 4 budget muscle cars - the Duster 340, the Dodge Dart Swinger 340, the Chevy Nova SS 350, and the Ford Mustang Mach 1 351 Cleveland - the Duster 340 won the 1/4 mile drag test and was the least expensive car in that group.