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The larger 750-cfm Speed Demon shined as the power numbers began to rise. Our dyno airflow meter showed almost a 20-cfm gain in airflow usage because these heads consumed 652 cfm at their volumetric peak.
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The peak horsepower numbers also screamed performance, boasting another best number of 399 hp at 5,400 rpm. Soon, the dyno showed 365 lb-ft of torque at 2,000 rpm, and moments later revealed a new best torque number of 434 lb-ft at 4,000 rpm. We checked each stud to make sure they were torqued, lashed the valves, and set the fuel and timing at their previous settings. Scoggin-Dickey also offers a large-runner 203cc Bow-Tie Vortec head for the high-rpm enthusiast.The OE Vortec heads feature pressed-in rocker studs, whereas the Bow-Tie version comes with 3/8-inch screw-in studs. The ports look very similar to the OE Vortec castings but are obviously designed to make power for the die-hard street enthusiast. The cool thing about the Bow-Tie Vortec head is that that it features both center-bolt and perimeter-bolt valve cover mounting bosses, plus, "Vortec" is cast into the head above two of the spring perches and a neat little Bow Tie Chevy emblem in the exhaust face of the cylinder head. "We ordered these heads from Scoggin-Dickey fully assembled and with a maximum valve lift good for 0.545-inch. Grind #119831 w-.509/528 liftīelow is the Scoggin Dickies vortec head for comparison : The airgap intake was used in a 355ci motor and a crane roller cam was used. Considering these heads weren't designed for performance, they did quite well."Īdvertised AirflowMeasured at 28 inches of H20 The average numbers were 393 lb-ft of torque and 289 hp across-the-board. Without a doubt, these heads would see a major improvement with a little polishing around the valves and porting the intake runners to match the intake gaskets. This told us that the small runners were restricting air through the cylinder head becuase the actual ports themselves were moving all the air they were given. What's interesting is that the little 165cc intake runner was able to consume a whopping 633 cfm at its highest point of volumetric efficiency. Peak horsepower was 384 at 5,400 rpm, showing a definite restriction in intake runner size. Soon enough, the engine was ready and we pulled the handle.Low-speed torque was down a hair, 361 lb-ft at 2,000 rpm, but peak torque was 424 lb-ft at 4,000 rpm. The Dart and Vortec both have center-bolt and perimeter-bolt valve-cover patterns, screw-in rocker stud bosses (studs not included), and feature the nicest raw casting of the bunch.
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One felt that the 165cc intake runner would limit intake flow while another thought that the 3cc (0.3:1 compression difference) larger combustion chamber would hurt torque across-the-board. We figured it would be interesting to see how well this OE replacement head would fair against performance pieces that were designed to make power.During the assembly session there was a sense of uneasiness in the dyno cell as each of us had our opinion as to how the Dart head would do.
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After numerous phone calls and a promise that we would be clear about the head's intention, Dart decided to join in the fun. Instead, it was conceived as an inexpensive OE replacement for major engine rebuilding facilities across the country, and that given the end user, Dart racing technology was not incorporated in this casting. Initially, we were told that Dart wasn't interested in competing in a power test because this particular head was not designed as a power piece.
#Summit racing head porting kit pro#
Dart Machinery is a high-tech company that uses its knowledge in NHRA Pro Stock racing to develop cylinder heads, blocks, and intake mani-folds for the high-performance enthusiast. Here are the results from the Summit/Dart vortec heads: I decided to go with Summit Racing Vortec heads.There is not much info on these heads and over the last month, or so, I decided to really dig into the internet and find the information I have desired.I found this information, since several have said that these heads are not as good as original GM Vortecs.Well, Chevy High Performance Mag did an article on ALL the vortec heads available out there. I am in the process of getting parts and a GM crate motor to put into my RV. Dart/Summit Vortec heads VS SGD Vortec heads