By the time Edelbrock's new aluminum big-block Mopar heads were introduced at the SEMA show last year, we already had a close-up look at the new aluminum castings at the Edelbrock's design and research lab. We reported those initial impressions in the Feb. '01 issue of Mopar Muscle and were generally pleased with the design. It wasn't the shiny-silver look of a fresh aluminum head that grabbed us, though; what really made them interesting were the nicely shaped port and bowl forms, the quench combustion chamber, and the deeper, angled spark-plug position. The clincher was when the factory engineers said, "Go for it!" when asked if we could run comparison flow bench testing versus a standard No. 906 casting. That final tally showed 291 cfm of intake airflow (against 233 cfm for a stock No. 906 casting) and 223 cfm versus 171 cfm on the exhaust side. It seemed as though some power would be had here.
While the design changes were obvious and the flow numbers looked promising, the bottom line is how they stack up in power production on the dyno. We already had a fresh '71 440 Six Pack motor on the stand (see sidebar, Builder's Notes-The Combo), so we ordered a set of the new Edelbrock pieces and headed to the Westech dyno. The rules were simple: start with a stock set of No. 906 heads, swap to an out-of-the-box set of Edelbrocks and see if they deliver the goods. Moreover, we brought along a couple of different Edelbrock intake manifolds, the old standard high-rise TM-7 single-plane, and the more recent Performer RPM two-plane. We'd run both intakes on both sets of heads and let the numbers tell the tale.
Baseline Our baseline combo consisted of our stout Comp Cams solid street roller- equipped Six Pack short-block with the ubiquitous No. 906s up top. The heads had the production valves and were unported, though a quality rebuild was performed, including a precision race-type valve job and a minor blend of the sharp bottom cut in the bowl. In other words, cheater No. 906's, but they were the stockest fresh heads we had available and representative of a well-detailed set of production units. Since we were running a solid roller cam, the appropriate dual valvesprings were installed to achieve the required spring loads and were bolted on with fresh Fel-Pro head gaskets. On the entry side of the heads, we installed the Performer RPM intake crowned with an 850-cfm annular discharge booster Speed Demon carb; on the exit side we bolted up a set of tti 2-inch primary headers.
After a few base pulls to establish the jetting (it turned out nearly dead-on out-of-the-box), we had the first numbers on our 440: 483 hp at 5,500 rpm and 529.7 lbs.-ft. of torque coming in at 4,000 rpm. Even with the relatively stock heads, the 440 was making serious power for a street engine. Credit the excellent Comp roller cam.
Next, we swapped to the TM-7 single-plane, an ancient design race single-plane that's still available new from Edelbrock. A retest with the intake change showed that power was down across the board when compared to the Performer RPM, with the figures now coming in at 517 lbs.-ft. at 4,100 rpm and 471 hp at 5,400 rpm. We already knew from previous dyno testing that the Performer RPM is tough to beat, even with a good single-plane intake, so the old TM-7 didn't have a chance, especially in the under-6,000-rpm power range of this street engine.