Big Bang For The Bucks

Pro Action Cylinder Heads Offer Intriguing Options

By Alex Walordy

In the far away land of New Zealand, advanced computer research is proving that lightning can mean more than thunder and huge blue sparks across the sky. This new kind of lightning comes in the form of small-block Chevy cylinder heads, and rather than lighting up the sky, it lights "win" bulbs quite regularly.

However, the need for speed began at a much different level. Craig Pullman of Pro Action Cylinder Heads was determined to have a foundry tied directly into a prototyping shop. In an unbelievably short time, he's able to transform an idea into a computer model and directly to an actual part. This gets components on the dyno quickly and makes ready to race parts available over the counter that much faster.

Whether his interests are toward cast iron or aluminum, angled or straight plug, or even gasoline or alcohol, he can have parts on the dyno quicker than most, and custom heads are not out of the question. Since the most popular cylinder heads in the aftermarket are 23-degree small-block Chevy units, he's focused plenty of time and effort into making his outstanding. Pullman has named his new line of cylinder heads "Lightning" for these reasons.

Craig teamed up with Ron Shaver Specialties of Torrance, California, to make these parts more readily-available to enthusiasts on this side of the Pacific pond. Shaver is a well-respected builder of competition powerplants in Southern California, especially in the world of 410ci, aluminum sprint car engines. His shop is equipped with the necessary five-axis CNC machines, computerized dyno equipment, and specialized flow benches to make the most of the Pro Action heads.

When Chevrolet first designed the small-block head in the mid-'50s, the valves were tipped at 23-degree angles relative to the deck of the head. Since that time, bores, valve sizes, and angle combinations have had countless changes. Shaver has explored Pro Action heads ranging from the common 23-degree angle all the way to an extreme 5-degree design, with 18-, 14-, and 10-degree heads all getting research time. Is 5 degrees the final limit? Shaver explains some valve angle is necessary to build height and plug angle, but with a good range of heads being made available, customers can now get what best suits their particular needs.

The Pro Action Lightning heads are well-regarded for their many features, including the ease of bolt-on Jesel rocker shafts (the larger thread inserts to retain them are included), off-the-shelf compatibility with many aftermarket intakes, and availability of more advanced designed intakes for those that need more.

ALUMINUM OR IRON?
Normally, rule books or personal preferences determine whether you'll be running cast-iron or aluminum cylinder heads, but the differences between the two materials are such that making the decision is becoming easier. Aluminum offers the ease of modification or repair, since it's easy to weld. Obviously, aluminum heads also offer weight savings over cast iron, and its heat conductivity allows for street use without as much concern toward overheating.

Iron aftermarket heads are not simply there to conform to some sanctioning body rules, as we've seen in PHR. You can build an amazingly strong nitrous-fed or supercharged powerplant with the thick-deck iron heads that will not bow under high combustion pressures. Pro Action Lightning iron heads are not engineered with a heat crossover in place, which is fine for street cars in warm weather and is not a factor in racing.

SPARK PLUGS
Pro Action offers head designs for either straight or angled plugs, which is nice if you've got access issues, rules limitations, or a preference based on your own experience or design. It's thought that angled plugs provide a better location for the spark plug gap, and with the flame kernel beginning closer to the exhaust valve (the hottest part of the combustion chamber), detonation is better avoided. The design of the engine also limits how much plug movement can occur in the cylinder head and still provide measurable benefit. Keeping the plug gap out of the way of the incoming charge means it won't get washed with fuel, and starting flame propagation at the hottest part of the chamber is the most power-producing way known. All of the Pro Action Lightning heads, whether aluminum or cast iron, use longer, 3/4-inch plugs, which gains some thread length for better cooling and can provide more timing latitude.

VALVES, SEATS, AND BOWLS
The valve bowls in the Lightning head designs have similar shapes and power producing features, based on the research done prior to their inception. The valve seats and bowl forming are all done on proven Serdi equipment for consistency and concentricity, as the heavy-duty spindles (an integral part of the Serdi equipment design) are much more consistent than hand-blending or grinding.

When it comes to sizing intake valves, a smaller-volume intake port is understood to be best fed by a 2.02-inch intake valve, but with a more efficient port larger valves can be used effectively. Valve diameters of up to 2.2 inches have been engineered into Pro Action Lightning heads destined for the track.

Most exhaust valves carry a diameter of 1.6 inches, although larger-diameter versions are commonly used in nitrous-fed engines where exhaust scavenging is more critical to power production. Often, a small reduction in the intake-valve diameter and an increase in exhaust-valve size results in greater power on engines destined for large servings of juice. The basic chamber shape remains the same, however.

As the valve opens, particularly with a 23-degree head, it gets closer and closer to the cylinder bore. Obviously, engines with larger bore diameters benefit from less shrouding of the valve. This can be a primary concern when designing the engine of your dreams.

The cast-iron heads manufactured by Pro Action all receive ductile iron seats, as opposed to sintered units. They are machined and pressed in, and have proven to be hard-wearing and compatible with leaded race fuels. They are comfortable running with either steel or titanium valves. Even when you pull the heads out of the box, you can feel the smooth transition between the iron head and the seat, and realize it is certainly no flow restriction. Pro Action's aluminum head valve seats are made of copper-beryllium, which run cooler in the aluminum heads than in cast-iron surroundings.

VALVESPRINGS
The cam lobe and the valvespring work together as a team, trying to provide fast and smooth valve action without undue stress. This isn't always easy, especially with more radical grinds, but the balance between high spring pressures and frictional losses from turning the cam must be in sync with the purpose of the engine. Obviously, a daily-driven street machine should not have the same seat pressure as a race-only engine, and the cam specs should be different as well. Finding the lightest-possible spring capable of doing the job is key, and its best to rely upon the cam manufacturer's recommendations here. Naturally, it's best to side with durability over light weight, and your chosen cam grinder should be aware of this.

To find space and support for bigger springs, we need help not only from the valvetrain, but also from the head itself. The 23-degree Lightning heads deliver with spring seats cut to 1.450-inch diameter, but the room exists to easily step up to 1.550-inch spring diameters without worry. With additional machining, springs of up to 1.625 have been installed in Lightning heads.

Dennis Hardesty, who has charge of the flow bench and porting services at Shaver Specialties, uses VSI spring seats with an integral shoulder. They pilot the inner springs and protect the head against the flat-wound spring damper to protect it from chewing up the aluminum. Attempts at running without a spring damper pressed between the inner and outer springs have proven unsuccessful.

Like diameter, increased spring length (or height) can reduce the unit stress of the spring wire and contribute toward longer spring life. To create added spring height, longer valves are used. Typically, .100-.200-inch longer valves are used in engines with standard port heights. With raised ports, it's not unusual for the valves to be as much as .700-inch longer than comparable stock units. Naturally, these longer valves are also heavier, and that may limit rpm more than the added spring tension, so it's important to do all the research on your particular combination before ordering anything. It is possible to run thinner valve stems to save on weight, but this also impedes durability. When switching to thinner stems, the only choice for valve material is titanium, and that carries a premium price tag. Any other material would bend from the stress.

VALVE GUIDES
Generally, a bare valve guide hanging into the runner is more turbulent and can impede flow. To streamline this area, Pro Action Lightning heads have directional fins located between the bowl and the guide, taking into account the fact that intake air is flowing into the engine while exhaust gases are moving out. On the intake side, the fin is trim and slim, and while it serves as a support for the guide, it carries away less heat. On the exhaust, a massive fin aids in carrying heat from the valve bowl wall. Shaver explains that this also helps keep the guide from "heat chipping."

The longer the valve stem is, and the greater the valvespring pressure is, the longer the guide should be. Pro Action uses manganese intake and phosphor bronze exhaust guides. Both come already cut for PC seals. These guides are superior to what you'd normally find in stock or even most other aftermarket heads, and allow tighter guide-to-stem clearances.

Dennis explains that a tight guide is a double-edged sword. The valve is under better control, so it stays more concentric and does not pound out the seat. A guide with tight clearance can live longer because the side loads are greatly reduced. On the other hand, a tight guide is more likely to stick, which is a recipe for instant destruction. It really pays to work with an experienced head shop here, since the proper compromise between not sticking and not being sloppy is what we're really after. Like everything else inside your engine, all of these clearances are affected by heat, so the dimensions become even more critical on street engines apt to swell in traffic. It's imperative to check for proper valve geometry when assembling the valvetrain.

PORT SIZING
"To win races, you've got to consider not just the steady-state flow numbers, but the port size at many different port cross sections," says Peter Hill. "Naturally, the final answer on what works is found at the track, but Shaver Specialties lists many vital dimensions at different sections of the intake and exhaust ports. This becomes important when tracking dimensions and researching combinations, and whether you should keep what you've got or modify it."

Hill, who works extensively in Pro Action's research and development department understands how critical port volume is, and you should too.

The best-possible port length for your combination is defined by the overall package. Weight, stall speed, gearing, and traction all play roles in selecting the proper-size port for your particular need. Port volume is normally referred to in cubic centimeters (cc). While this is a good number to know, the measurement does not define the shape or length of the port. In general, port cc, valve size, and a ton of development work are what set the limits for flow and velocity. While more port cc can be gained as a result of porting, there is a definite difference between intelligent cc gains and general hogging out. Lightning head ports are designed to Pro Action's latest computer and dyno findings, and seem to be somewhat larger than usual. As street enthusiasts, we know the importance of velocity in an intake port to increase the kinetic energy of the incoming air/fuel charge. For this reason, Shaver often adds specific CNC work to the Pro Action Lightning designs on his own equipment to maximize efficiency on each specific application.

A moderate 350ci small-block Chevy destined for street greatness runs best with a 180cc intake port. A 400ci engine headed for the streets prefers a 200cc port. The same 350ci engine armed with more cam and pulling 4.56:1 rear gear would also like a 200cc port. A roundy-rounder running a 406 with a big cam and tight gears in a lightened chassis could use a 220cc port to pull hard out of the corners. If you've got a quarter-mile rail that launches off the trans-brake and sings to 8,000 rpm, you'd be looking at a raised runner 23-degree design with 250cc ports. This high-rpm application could also take advantage of an angled plug and a tight 54cc combustion chamber to feed its high-compression diet of race gas.

When an as-cast port is CNC-machined, it becomes roughly 5cc larger and very consistent. The intake surface texture left by the machining process will benefit power by peeling off any liquid fuel that attaches itself to the port walls. The machine finish left by CNC equipment could be polished smooth with hand blending, but keeping air and fuel in suspension requires some surface roughness to keep turbulence near the surface. Most CNC-finished intake ports could also be helped with a little seat and chamber blending. When these parts are machined during assembly, the seat material is removed at a different rate than the surrounding head material, so a little cartridge roll work is all that's usually necessary.

PORT SHAPES AND LOCATIONS
On the new Lightning heads, the floor location has been left pretty much as stock, but the port widths and heights have been worked over for better flow. Raising the port roof has shown the best gains, and always shooting for a straighter shot at the valve has helped power levels and established the target for cylinder head experts. It's this straight shot approach that got the valve angles moved, and this has shown major gains in flow volume, too.

In addition to changing port shape and size, Pro Action has also experimented with moving port location. For example, on the small-block Chevy, one of the hottest parts of the engine is directly between the center exhaust ports. Pro Action moved these ports apart and made room for improved cooling. On the 14-degree head with spread ports, the head gaskets have found more life from reduced temperatures in this area. All of these improvements and innovations in design are worth real power, as Pro Action claims gains of 30-100 hp over traditional head designs. Naturally, these mods require specific valvetrain and exhaust header components to work at all, so none of these gains come without a price. Considering most competition powerplants already run shaft rockers and custom headers anyway, the real impact of these additional expenses is minimized if Pro Action heads are considered from the start.

SUMMARY
When considering the ever-popular small-block Chevy as a powerplant for your project, do the research necessary to determine the best-possible combination for your application. If a serious small-block is what you're after, the Pro Action Lightning series of small-block Chevy heads is certainly a good start toward a screaming engine. By working with a pro like Shaver Specialties, you're sure to end up reaching or surpassing your target horsepower level. The wide range of features and options offered on the Pro Action Lightning cylinder heads can certainly help you tailor your powerplant to your own needs, and that's what hot rodding is all about.