How to build a 13 second 340 Duster

Well, some depends on gearing and how well you can stick the tires and shift. My old '74 Barracuda was a 340 4sp (original 318/3sp) with 3.23 sure grip. The engine was a ring and bearing job on a '68 340, I ran a Comp Magnum 268H cam, matched springs, a '71 Thermoquad intake and carb, and 1 5/8 cheapo headers. I could run a 13.0 on Dunlop radials. With the NOS, it went 12.50s without using in in 1st, and spinning the same radials when it hit.

That was the 80s. With better machining and parts, you should be able to run 13.0 easy. I'd run KB243 hypereutectics set to 0 deck, stock rods, stock crank, file to fit rings, factory heads with either 1.88 or 2.02 intake valves (doesnt really matter to me), have a good 5 angle vlave job, replacing anything that is marginal. Static compression with a typical Fel Pro gasket comes out around 10:1 normally, depending on how big the cahmbers are. The valve job is the single most important thing you pay for. Make sure it's a good one, on good eqiupment. For a cam, an XE268 with matching springs. I'd keep the Thermoquad and intake. They are quite good. If you want to upgrade, the Edelbrock RPM airgap with an Edelbrock Thunder AVS would be my coice for it. In a Dart, that is enough for under 13.0 running a street friendly 3.55s of 3.91s, and with you using a tire that can stick.