In the early-'90s, GM introduced the Second-Generation LT1 small-block. It featured reverse-flow cooling and an aluminum cylinder head with a new port configuration. In essence, the company created the best small-block Chevy cylinder head ever put into mass production. It was released on top of the '92 LT1 Corvette engine and later on the '93 LT1 Camaro. The new port/chamber design that began life as an aluminum casting eventually carried over in a cast-iron version. Unfortunately, just as the LT1 concept began its ascension, GM executives decided to put an end to its production. This superstar cylinder head dropped off the performance map because both the aluminum and cast-iron heads lacked a coolant crossover passage, rendering them useless to any engine series other than the discontinued LT1.
The LT1 prospered from 1992 to 1996 in various vehicles, but its days were numbered. In 1997, GM released its Third-Generation small-block engine, the LS1. While the new Corvettes and Camaros were about to receive yet another cylinder head breakthrough, the engineers at GM's truck division knew that the LT1 port still had something to offer. Subsequently, the '96 truck engine series hit the market with the infamous LT1 port in cast-iron production. It was called the Vortec design and became the most efficient mass-produced small-block Chevy cylinder head ever created.
When Chevy enthusiasts discovered the capabilities of the Vortec head, it didn't take long to take advantage of its coolant crossover passages and fit them to First-Generation small-blocks. As if building the ultimate OE street-performance head wasn't enough, GM Performance Parts sweetened the deal even further by announcing that each head could be obtained fully assembled for approximately $250.
The cast-iron Vortec heads were released in 1996 and produced through 2001. Abetted by a newly redesigned coolant crossover passage, these heads could be bolted directly onto a First-Generation small-block engine with the help of some aftermarket parts. The intake face of a Vortec head is cut at a slightly different angle than the First-Generation SBC heads and features an eight-bolt-hole intake manifold hold down as opposed to the standard 12-bolt design, so a special Vortec intake manifold and gaskets are required to put the Vortec heads on top of a First-Generation small-block. Furthermore, the OE-production Vortec valvetrain requires a self-guided rocker system that will not exceed a maximum valve lift of 0.420 inches unless the valvetrain has been modified. For more details about Vortec head installation onto a First-Generation small-block, visit our Web site at www.chevyhiperformance.com or dig up a Jan. '03 issue.
Now that the history of the Vortec port/chamber design is clear, we can move onto this month's king-of-the-Vortec-head test. We ordered every example on the market in applications featuring 185cc intake runners or smaller; the idea being that a Vortec head is a low-cost street piece and should be tested in a street fashion. Our evaluations would be run across a 0.030-inch-over bore 350ci short-block featuring all remanufactured OE parts that had been balanced and blueprinted by Hye-Tech Performance. Hye-Tech offers this assembly for $900 less oiling, timing cover/chain, and camshaft, or fully outfitted for a few dollars more.
To finish it off, we secured a Moroso baffled oil pan, pump, and pick-up, and then moved to the valvetrain side with a Crane Cam setup featuring everything but valvesprings, retainers, locks, and rocker studs. Once the cam pieces were lubed and set in place, we installed 0.040-inch-thick Fel-Pro reusable MLS (multi-layered steel) head gaskets. Since we'd be swapping five sets of heads, these reusable gaskets would cut the interchanging parts cost and offer consistency between tests.
We began with the OE Vortec casting that had only been valvetrain-modified by Scoggin-Dickey to accept valve lift up to 0.600-inch. We fastened them to the block using ARP head bolts covered in thread sealant. After torquing them to 65 lb-ft, we added a 1 5/8-inch primary pipe, long-tube Hedman Headers; proceeded to install the rest of the valvetrain; and lashed the valves on the self-guided rocker arms. We covered the assembly with center-bolt Proform valve covers.
At this point, the Edelbrock dual-plane RPM Air-Gap intake manifold was ready to go on. With silicone under the front- and rear-lifter valley rails and the Fel-Pro gaskets in place, we lowered the intake on top of our Vortec heads and tightened the eight fasteners in a cross pattern. We topped it off with a 650-cfm Speed Demon mechanical secondary four-barrel carburetor and finished the assembly with a Pertronix HEI distributor sprouting matching wires held in place by Made For You Products wire looms.
To even the testing ground for all of the heads, intake runners of 185 cc's-or-smaller would ensure every head was a true street contender and offer consistent torque at all engine speeds. All tests would be on 91-octane pump gasoline, which is why our Hye-Tech mule motor had its valve-relieved Speed-Pro pistons sitting 0.010-inch in the hole. When combined with the 0.040-inch-thick head gasket and 64cc to 67cc combustion chambers, the compression ratio would range from 9.7:1 to 10:1. With our camshaft specs, the motor was set up to pull 14 inches of vacuum at 800 rpm while running 36 degrees of total advanced timing. The key to running a 10:1 compression ratio with iron heads lies within the spark curve, which is why we used a box-stock Pertronix distributor set-up with a rather slow advance. By keeping timing out of the cylinders at high load/low rpm, the motor stayed out of detonation and made power across the entire rpm curve. Two other variables that we'd monitor and steady for consistency were the engine oil and water temperatures. Hot oil reduces friction, so we kept ours at approximately 180 degrees while the water circulating through the block and heads was kept as close to 160 degrees as possible. With all our variables under control, we were ready to begin.
The first test called for a baseline run using the OE Vortec heads. While the factory GM versions can only handle 0.420-inch valve lifts, we used modified valvetrain Scoggin-Dickey versions that accommodate a valve lift of 0.600-inch. No port modifications were made and the valves and valve job were untouched. The OE Vortec heads come fully assembled with 3/8-inch rocker studs and require a center-bolt valve cover. We used polished Proform rocker covers that proved sturdy from test to test and looked good as well. The only area of concern here is that some valve covers, like our Proform pieces, may have breather interference issues with certain rocker designs. The internal baffles can be removed and upgraded using an external breather design if clearance becomes an issue.We were surprised at how well the OE Vortec cylinder heads performed against the various aftermarket versions. Our first pull delivered some good numbers, but the dyno showed a reading of 633 cfm being consumed by the little Mouse. While our Speed Demon carburetor was rated at 650 cfm, we felt there may be a bit more power in a 750-cfm Speed Demon application. We watched the numbers climb: An amazing 364 lb-ft of torque at 2,000 rpm rocked the dyno screen and the motor was well on its way to posting a peak torque of 431 lb-ft at 4,000 rpm. In kind, the horsepower number was 391 at 5,400 rpm. So the OE Vortec really shined and left little room for the competition to claim a spot in our winner's circle. The average power numbers of 400 lb-ft of torque and 293 hp are good enough to move a 3,200-pound car to a solid 13-second quarter-mile time.
|Advertised Airflow Measured at 28 inches of H20|
After testing the untouched OE Vortec versions we wanted to see how lightly hand-ported pieces would do in comparison. The heads were the same part number as the previous ones, but touched-up using a Standard Abrasives porting and polishing kit. The actual amount of material removed was very minimal because no carbide cutters were employed. We rounded sharp edges to help create a smooth, flowing port. On the Superflow flow bench, our hand-ported parts delivered roughly 5-15 cfm more flow than the stock version and made us curious as to what the dyno would have to say.We fastened our ported Vortec castings to the Hye-Tech motor using the same Fel-Pro MLS head gaskets and ARP head bolts. Then we hooked the fuel line up to the 750-cfm Speed Demon carburetor and set the timing at 36 degrees. Our first pull delivered a slight gain in low-speed torque, posting 369 lb-ft at 2,000 rpm and a peak of 434 lb-ft at 4,000 rpm. So our home-porting job had moved the powerband up 100 rpm and delivered a peak horsepower number of 394 hp at 5,500 rpm. Though not much of gain, we felt it was still worth noting for grind-happy enthusiasts. In all, the average power numbers showed a gain of 3 lb-ft of torque and a loss of 1 hp.
|Advertised Airflow Measured at 28 inches of H20|
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.
|Advertised Airflow Measured at 28 inches of H20|
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.
|Advertised AirflowMeasured at 28 inches of H20|
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.
|Advertised Airflow Measured at 28 inches of H20|
During the testing, certain parts interfered with others, due to sizing variances. In an aftermarket version, it's not uncommon to see extra material around a stress-related area. Currently, companies like Edelbrock, Professional Products, and Weiand, are all making aluminum Vortec intake manifolds for carbureted applications. Other companies, such as Crane Cams, Comp Cams, and Proform Products, offer special Vortec self-guided roller rockers arms in 1.5:1 and 1.6:1 ratios. These parts are specific to Vortec applications and have slightly altered measurements as compared to stock GM parts. Whenever ordering cylinder heads, find out whose rocker arm will fit the head and valve-cover application. Also, make sure the heads have rocker studs and either guide plates or self-guided rockers. Below is a list of complied parts that were interchanged on our Hye- Tech short-block to test each of the heads.