Words And Photos: Jeff Smith
Let’s get this over with right now – if you will accept the concept of strength in numbers, the small-block Chevy is still the king. Sure, the LS family deserves all the hyperbole. But that doesn’t change the fact that there are more traditional small-block Chevys running around wild in the streets in hot street cars than all the others. It’s probably etched in a stone table somewhere. There are still rodders interested in budget-based small-block Chevy stories and this one deserves updating.
If you’re on a Mac ‘N Cheese budget but you’d still like a little torque under your right foot, you’ve probably heard about the power payoff of Vortec heads. For those who may be new to the game, the Vortec head was first introduced on the L31 350ci truck engines in 1996. Despite their journeyman use, these heads flow dramatically better than any other small-block Chevy production head, which makes them popular with just about anybody who wants to build a mild street small-block. Used Vortecs are still around or you can purchase these castings brand new from Chevrolet Performance. We found them on Summit Racing’s website for less than $330 apiece – complete and ready to run.
While these heads will bolt right on a small-block Chevy, there are several caveats that you should be aware of before you torque those head bolts down. First, these heads employ a unique 8-bolt intake bolt pattern that’s different compared to the standard small-block Chevy 12-bolt pattern, requiring a dedicated Vortec manifold. Next, the Vortec head employs a small, 64cc combustion chamber. This is great for stock short block 350 engines like the Chevrolet Performance 290 hp 350 crate engine that uses a dished piston with a 76cc combustion chamber head. That creates an 8.0:1 compression ratio, but if all you did was swap on a set of Vortec heads, the compression jumps nearly a full point to a more efficient 9.0:1. With a common, four-eyebrow flat top piston and a .041-inch thick head gasket on a 350ci engine, the Vortec head will bump the compression to around 9.5:1 depending upon the deck height.
There are other, smaller points that are important to know because they affect cam selection. If you intend to run a very mild cam with less than 0.440-inch lift, then simply bolt these Vortecs on and have a nice day. But today, even a stone stock 5.3L LM4 LS truck engine sports 0.466-inch lift, so building a street Vortec-headed small-block demands a cam with at least 0.475-inch of valve lift. But there’s the rub. The stock Vortec iron head will not tolerate more than 0.440-inch lift. We measured our stock iron heads right out of the box and the retainer-to-seal clearance was only 0.470-inch. Subtract the standard 0.050-inch clearance, this leaves only enough room for a 0.420-inch lift cam. That just won’t do. But don’t despair. Just get out your tools and make some modifications.
While some hot rodders would probably take their heads to their favorite machine shop and let their shop do the mods, we’re here to tell you that the mods these heads need are easy to do yourself with a custom milling tool, a ½-inch drill motor, and a clean spot on the work bench can accomplish.
The Vortec head features a very large boss at the base of the valve guide that measures 0.850-inch in diameter and is used to locate the 1.250-inch outside diameter (O.D.) valve spring. The head uses 0.560-inch I.D. seals mounted directly on the top of the guide. This guide boss is also very tall. This height restricts the room between the top of the seal and the bottom of the valve spring retainer at max valve lift. There are two simple approaches to modifying the head to accept a performance valve spring that will create the room necessary to allow greater valve lift.
The easiest solution is also the most expensive. COMP Cams builds a beehive style valve spring that drops right in place of the stock spring along with new retainers and valve locks. The beehive spring uses a much smaller retainer that produces additional clearance to the stock seals. With the beehive, this instantly improves the retainer-to-seal clearance to 0.500-inch, which means you could run a 0.470-inch lift cam with a tight 0.030-inch clearance. The beehive springs we chose (PN 26915) drop right in place and no machine work is necessary and even the original seals can be reused. The detraction to this approach is cost – the beehive springs are more expensive than a conventional spring and with retainers and locks, the price comes to roughly $260.
The second solution is less expensive but requires more effort and to purchase a machine tool to modify the valve guide boss to add clearance. COMP sells a slick little tool that will machine the guide down to a 0.530-inch O.D. seal size while also lowering the boss height. The boss height of our heads measured 0.730-inch from the spring seat. It is this height that minimizes the seal-to-retainer clearance. With the tool set up in our ½-inch drill motor, it took a few minutes to machine all 16 guide bosses, being careful to lower the guide height only enough to create 0.550-inch retainer-to-seal clearance. We discovered that our 981 spring would just clear the wider base after the top of the guide was machined because the damper was the only portion of the spring that hit the guide boss. If spring shims are required to set the installed height, you will need shims with an inside diameter of 0.875-inch to clear the guide boss. COMP also offers another machine tool that will narrow the guide boss and also increase the spring seat diameter, but we elected not to use that tool. With our machining completed, we cleaned all the cast iron shavings, reassembled the heads, and the job was complete.
For those who would rather buy a set of heads already converted, Scoggin-Dickey Parts Center in Lubbock, Texas offers several options that are a good deal. We did the math and if you have a set of used Vortec heads, the conversion to the COMP 981 springs will cost $236. But if you are considering buying a brand new set of Vortec heads, Scoggin-Dickey offers an already modified and assembled Vortec head. The guides are machined to increase retainer-to-seal clearance to accept 0.0525-inch valve lift and the heads include a set of Z28 springs and retainers. You might as well buy the Scoggin-Dickey heads because their price is almost exactly the same. We couldn’t find the specs on the Z28 springs but we’ll assume the springs are roughly equivalent to the COMP 981 springs.
Just to give you yet another option, Chevrolet Performance also makes what is called a Vortec Bow Tie head in two different port sizes. Both the small- and large-port heads feature 2.00/1.55-inch valves, 66cc combustion chambers, are drilled and tapped for screw-in 3/8-inch rocker studs (no guideplates), the intake port is drilled for either the typical Vortec patter or for a tall port conventional small-block intake manifold bolt pattern. Finally, these heads offer both a perimeter small-block valve cover bolt pattern and the center-bolt configuration. The small intake-port version measures 185cc (larger than the stock Vortec) while the large-port measures a much larger 225cc. These heads are only slightly more expensive than the modified stock Vortec head and offer some significant improvements.
So the Vortec cylinder head landscape has changed a little over the years with plenty of options for those willing to do a little work. As the great Mark Twain once wrote in Huckleberry Finn, “You pays your money, and you takes your choice.”
Valve Spring Chart
|Valve Spring Description||Seat Load at Install Ht.||Open Load at 0.500” lift||Rate|
|COMP 981 Single w/ damper||105 lbs. at 1.700||291 lbs.||373|
|COMP 26915 Beehive||105 lbs. at 1.800||261 lbs.||313|
|COMP 26918 Beehive||125 lbs. at 1.800||311 lbs.||372|
|COMP Valve spring, single 1.25” dia.||981-16||Summit Racing||$63.97|
|COMP Retainer for 981 spring||742-16||Summit Racing||$54.97|
|COMP Valve locks for 11/32” valve||648-17||Summit Racing||$25.97|
|COMP Valve spring, beehive||26918-16||Summit Racing||$180.97|
|COMP Retainer for beehive spring||774-16||Summit Racing||$53.97|
|COMP Valve guide seals||514-16||Summit Racing||$17.97|
|COMP Valve guide cutter||4726||Summit Racing||$46.97|
|COMP Arbor for 11/32” valve||4732||Summit Racing||$23.97|
|COMP Valve spring seat cutter||4721||Summit Racing||$55.97|
|COMP Valve spring seat cutter||4718||Summit Racing||$75.97|
|COMP Valve spring height micrometer||4928||Summit Racing||$71.97|
|COMP Valve spring compressor||5333||Summit Racing||$179.97|
|Chevrolet Perf. Vortec iron head||12558060||Summit Racing||$329.97|
|Chevrolet Perf. Small Bow Tie Vortec||25534421||Scoggin-Dickey||$504.95|
|Chevrolet Perf. Large Bow Tie Vortec||25534446||Scoggin-Dickey||$499.80|
|S-D modified Vortec head w/ Z28 spring||SD-8060A2||Scoggin-Dickey||$445.87|
Scoggin-Dickey Parts Center