King Vortec

GM Bow-Tie Vortec Intake... 

   

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GM Bow-Tie Vortec
Intake runner: 180cc
Combustion chamber: 65
Intake valve: 2.00-inch
Exhaust valve: 1.55-inch
Maximum valve lift: 0.545-inch
Material: cast-iron
Fully assembled: PN 25534421
Price: $980
Average torque per dollar: $2.43
Average hp per dollar: $3.33

We ordered these heads from Scoggin-Dickey fully assembled and with a maximum valve lift good for 0.545-inch. 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. The ports look very similar to the OE Vortec castings but are obviously designed to make power for the die-hard street enthusiast. 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. We checked each stud to make sure they were torqued, lashed the valves, and set the fuel and timing at their previous settings. 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. The peak horsepower numbers also screamed performance, boasting another best number of 399 hp at 5,400 rpm. Our dyno airflow meter showed almost a 20-cfm gain in airflow usage because these heads consumed 652 cfm at their volumetric peak. The larger 750-cfm Speed Demon shined as the power numbers began to rise. Looking back, we were sure that we could have squeezed one more horsepower by cooling the engine or altering the air/fuel mixture. Overall, the average power numbers displayed a stout 403 lb-ft of torque and 294 hp. Porting and polishing these heads would most likely reveal a bit more power, but we decided to save this test for another day.

Dart OE replacement Vortec... 

   

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Dart OE replacement Vortec
Intake runner: 165cc
Combustion chamber: 67cc
Intake valve: 1.940-inch
Exhaust valve: 1.50-inch
Maximum valve lift: 0.620-inch
Material: cast-iron
Fully assembled: PN 10024370A
Price: $711
Average torque per dollar: $1.81
Average hp per dollar: $2.46

Now for the aftermarket. 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. 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. 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. After numerous phone calls and a promise that we would be clear about the head's intention, Dart decided to join in the fun. 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. 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. 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. 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. Peak horsepower was 384 at 5,400 rpm, showing a definite restriction in intake runner size. 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. 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. 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. The average numbers were 393 lb-ft of torque and 289 hp across-the-board. Considering these heads weren't designed for performance, they did quite well.

Edelbrock E-Tec Intake... 

   

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Edelbrock E-Tec
Intake runner:170cc
Combustion chamber: 64cc
Intake valve: 1.94-inch
Exhaust valve: 1.55-inch
Maximum valve lift: 0.575-inch
Material: aluminum
Fully assembled: PN 60979
Price: $1,080
Average torque per dollar: $2.65
Average hp per dollar: $3.63

The Edelbrock E-Tec was the only aluminum head in the test. It is offered in a 170cc intake runner version or a larger 200cc intake runner size (also with larger valves), but they didn't fit our test perimeters. The E-Tecs are cast with perimeter-bolt and center-bolt valve cover bosses and come fully assembled with guide plates and rocker studs. If the guide plates are used a standard rocker arm is required. However, if you have self-guided rockers on-hand, the guide plates can be removed and washers can be installed under the screw-in rocker studs. The aluminum pieces look cool and are better able to disperse heat from the combustion chamber to allow a higher compression ratio. Since the Hye-Tech small-block was already on the edge of pump-gas compression using cast-iron cylinder heads, to keep the testing fair we left the compression ratio alone. As an added attraction, the E-Tec head weighs nearly 20 pounds less than its cast-iron counterpart.The slow speed numbers showed the lowest torque numbers of all at 360 lb-ft, but as the engine picked up speed, so did the power potential, posting 437 lb-ft of torque at 4,000 rpm and 408 hp at 5,500 and 5,600 rpm. Obviously, Edelbrock engineers spent some time inside these heads, because they bested the previous GM Bow-Tie numbers by 3 lb-ft of peak torque and 8hp peak. But what really matters in a street engine is the average numbers, and again, the E-Tec heads posted an average of 408 lb-ft of torque and 297 hp. The aluminum E-Tec heads edged out the GM Bow Ties by an average of 5 lb-ft of torque and 3 hp.