1970 340 High Performance Mill Dyno - Dyno Derby 340

Last month, we endeavored to build a '70 340 High Performance mill as close to factory original specifications as possible, just to see how much power one of these engines would really make. The plan was to use this as a baseline, and then add a careful sprinkling of aftermarket components to see if they delivered more power for the already stout factory package. Would it work? The fresh but bone-stock 340 was loaded up, and we headed to Westech Performance Group, one of the premiere independent dyno facilities in the country, to let the 340 show its stuff.

Phase I: Stock As A Rock
For the baseline dyno pulls, the engine was mounted to Westech's Superflow 901. At this stage, the engine was dressed out with the rare factory 340 HP exhaust manifolds, the original '70 cast-iron dual-plane intake manifold and an original 340 manual-trans Carter AVS carb. The cam was a factory 340 HP reproduction from Super Stock Industries (PAW), linked to the valves with the original stock solid pushrods and nonadjustable stamped-steel rockers. We used Chrysler's electronic ignition rather than the authentic dual point from the day.

Experience shows that the electronic and the dual point will produce the same output, if both are functioning properly. The electronic got the nod purely from reliability and consistency, and because these days they probably outnumber the dual point 100:1. The distributor was a remanufactured unit from Pep Boys, switched by a Borg Warner ECU, also from the 'Boys. A Mopar Performance wiring kit (#P3690152) and ballast resistor (#P5206436) linked the relative components. When we arrived at Westech, Steve Brule cut a fresh set of MSD wires and the 340 was ready to run.

The 340 fired on the first spin of the crank, and was given the customary 20-minute break in. We loaded the Superflow, pulled the handle, and had our baseline figures: 281.3hp at 5200 rpm and 328.5 lbs/ft at 3900 rpm. The factory rating on the 340 HP was 275hp at 5000 rpm, and 340 lbs/ft at 3200 rpm. Our 340 had topped the factory rating by a handful of horsepower, but was all well? Crunching the numbers from our baseline dyno sheet, it was clear that the mixture was too lean for peak power. Although the AVS carb was sporting the original jets, there were likely internal problems not remedied by our hasty soak and carb-kit rebuild (this carb began as one of the roughest and filthiest cores we've ever rebuilt). A jet change may have gotten us the fatter mixture the engine needed, but the jets were frozen in place with corrosion. Still, the 340 exceeded the factory power rating, and it was time to move on to Phase II.

Phase II: Edelbrock's Big Carb
Last year, Edelbrock unveiled a new 800 cfm version of its AFB carb. Similar to the AFB used as OEM equipment on some performance Mopars, the new 800 cfm Edelbrock carb is larger in terms of airflow than any of the OEM Carter AFB or AVS carbs. Those old enough will remember that it was popular to swap out the original small AVS (about 600 cfm) for the larger bore version (about 750 cfm) from the 440 Magnum. It was no secret back then that the 340 responded favorably to the increased carb capacity, suggesting that a larger carb would add to the horsepower bottom line.