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 The iron GM Performance Parts...  The iron GM Performance Parts Vortec head has got to be the best deal in town. |
 You can make 400 hp with ...  You can make 400 hp with a mild street 350 small-block using an unported set of these heads available complete for $480 a pair. |
 The Vortec heads come with...  The Vortec heads come with a very efficient 64cc chamber using 1.94/1.50-inch valves. Despite the conservative valve sizes, these heads flow extremely well in the 0.300- and 0.400-inch valve-lift areas. Both the intake and exhaust valves incorporate a 30-degree back-cut. |
 The stock springs will only...  The stock springs will only accommodate around 0.420 inch of valve lift. Other limitations of the Vortec heads include the press-in rocker studs and the required use of center-bolt valve covers (arrow). |
 The easiest way to identify...  The easiest way to identify a Vortec head is by the sawtooth pattern cast into the front. Look for casting number 12558062, but avoid casting number 10239906, which has a modified exhaust seat and loses 20 percent of its flow at 0.120-inch lift. |
 One area that can trip you...  One area that can trip you up when selecting a performance valvespring is this large guide- boss diameter of 0.900 inch (arrow). Most performance valvesprings have a smaller inside diameter, which requires this boss to be machined down to about a 0.630-inch diameter. |
 The Vortec head also uses...  The Vortec head also uses guided rockers to position the rocker arm over the valve stem. If you choose not to run guided rockers, then you must add guideplates to the heads with screw-in studs. |
 GM offers an excellent stock...  GM offers an excellent stock intake-manifold gasket that uses pins that precisely locate the gasket on the head. It requires no adhesive and uses silicone rubber seals around the ports. The Vortec head requires the late-model eight-bolt intake bolt pattern. |
 The GM valve-guide seals (0.560-inch...  The GM valve-guide seals (0.560-inch boss) are excellent items, but when the guides are machined, the valve-stem seal boss is generally cut to 0.530, which requires aftermarket seals. |
 There are several center-boltstyle...  There are several center-boltstyle valve covers available for the Vortec heads. You can even bolt on TPI-style magnesium covers, but these require minor machine work to clear roller rockers. |
 Additional valve lift from...  Additional valve lift from a big cam and/or 1.6:1 rocker arms will require minor pushrod hole modifications to prevent bent pushrods. You can perform this modification yourself with a drill motor and a 1/2-inch bit. Be sure to drill at the pushrod angle. Comp sells a tool that helps position the drill bit properly. |
 Using the Comp Cams tool with...  Using the Comp Cams tool with a handheld drill motor, we machined the valvespring seats out to 1.440 inches and reduced the guide diameter and the height with the second Comp tool. But even with better springs, you are limited to about 0.525-inch lift before you encounter coil bind. CHP |
Weve been getting a ton of mail with questions about how and when to modify the Vortec small-block iron headsso much mail that we decided to condense all the Vortec information into one concise story that should answer almost any question you have about this powerful iron cylinder head.
The Early Days
In 1996, GM incorporated the port design from the very successful iron LT1 engines used in the Impala SS, which was improved over the aluminum LT1 Corvette and Camaro engines. In essence, the Vortec head uses the iron LT1 chamber intake and exhaust ports in a standard-water-flow iron head. These production Vortec heads were used in the new Vortec 350ci engine intended for ½-, ¾-, and 1-ton Chevy pickups. Amazingly, this mundane, production-based 1.94/1.50-inch valve head performed better than the iron Bow Tie head. The deal of century occurred when GM Performance Parts decided to sell these heads as complete units for under $500 per pair, ready to bolt on. For you junkyard hunters, be forewarned that some ¾- and 1-ton trucks came with Vortec heads equipped with a specially hardened exhaust seat that kills low- and mid-lift flow. Casting number 10239906 should be avoided.
Chevy enthusiasts quickly discovered that these heads are capable of 400 hp right out of the box when teamed with a performance intake and a camshaft. But there are several changes that must be made before bolting this head onto your engine. Well run through all of them here and offer a few recommendations based on our experience.
Bolts, Springs, and Such
There are several important requirements dictated by the use of the Vortec head. The most important detail is that the Vortec uses an eight-bolt intake-manifold pattern that is different from the standard 12-bolt pattern. The Vortec requires a specific Vortec intake manifold available from both GM Performance Parts and Edelbrock. On dozens of dyno-tests, we have had the most success with Edelbrocks Performer RPM and the RPM Air Gap models. Professional Products also offers a specific Vortec intake. The intake ports are also significantly taller than typical small-block ports. While companies such as Jim Pace offer modified heads that will accept a standard 12-bolt intake, this requires a manifold with at least a 0.325-inch-tall sealing surface above the top of the intake port.
Most street intakes require welding and machining to create the proper sealing area. This is both expensive and time-consuming. Using a dedicated Vortec manifold is the best choice and probably less expensive.
The Vortec head also requires the use of center-bolt valve covers, and the good news is there are several styles to choose from. If you decide to use Corvette-style covers, you will have to trim the driprails inside the covers with a die grinder if you opt for roller rockers. Crane offers narrow-body rocker arms designed to work with center-bolt valve covers, but these are more expensive than standard roller rockers. Stock Vortec heads come with pressed-in 3/8-inch rocker studs and do not use guideplates. The rocker arms are guided (also called rail rockers) and employ a pair of guides or rails that center the rocker arm over the valve. This eliminates the need for pushrod guideplates. GM Performance Parts, Crane, and Comp offer self-aligning stamped-steel and roller-rocker arms that will bolt right on. Or, you can modify the heads to add screw-in studs and guideplates and then use conventional rocker arms, but be forewarned that this can add over $200 to the cost of the heads. Do not use guided or self-aligning rocker arms with heads that use guideplates, since this will cause pushrod bind and excessive wear. Also be aware that 1.6 rockers move the pushrod very close to the pushrod hole. Elongating the pushrod hole should be considered essential when using 1.6 rockers.
This leads us to valvesprings, which require the most attention in a performance application. Since this is an OEM iron head, GM designed the valve guide to also serve as the inside diameter (id) locating device for the valvesprings. The guides large diameter acts like a sleeve that keeps the single-wire valvespring located >> properly. The guide is also machined at the top to mount a positive-style, 0.560-inch-diameter valve-guide seal. All of this conspires to limit total valve lift to a safe figure between 0.420 and 0.430 inch. The limitation is the clearance between the bottom of the retainer and the top of the valve-guide seal.
Accommodating more valve lift requires modifications to the valvespring seat and valve-guide areas of the head. The best route is to increase the spring-seat diameter from the standard 1.25 inches to 1.440 inches. Both Comp and Crane offer tools that use a valve-guide arbor to position the cutter. The Comp Cams cutter increases the spring-seat diameter while simultaneously reducing the outside diameter (od) of the guide boss. The Crane tool also cuts the valve-guide-seal diameter at the same time. Comp sells a separate tool that cuts a new guide seal and reduces the guide height to create additional retainer-to-seal clearance. Both cutters machine the top of the guide down to a 0.530-inch diameter, which is the standard size for positive-type aftermarket seals. This requires purchasing new valve-guide seals, since the factory uses a 0.560-inch guide to locate the seals. Another way to go is to have a machine shop cut the guide boss diameter to around 0.760 inch and reduce the seal height and use either the Crane H-11 tool steel spring (PN 99846) or the Comp spring (PN 981).
Once these machining operations have been completed, you have the choice of several aftermarket valvesprings to match your cam profile. These machining operations will produce enough clearance to allow between 0.525- and 0.550-inch valve lift before running into valvespring coil-bind. Given a 1.440-inch valvespring seat diameter, Comp and Crane offer several single and dual springs that will work with the stock valves.
The Vortec heads offer a wealth of power potential for their extremely low price. In several tests of these heads, weve been able to make 400 hp and excellent torque with a relatively mild camshaft. If you include the cost of machine work and better valvesprings, the price does escalate a bit, but 400hp potential without porting with a stock set of iron heads is hard to beatespecially for so few dollars. Small-block street performance doesnt get much easier or cheaper than this.