The real world, where most of us except for a lucky few Winston Cup teams exist, can often be a painful place to live. Money is real and quite often difficult to come by. That fact puts a crimp on how most of us can effectively chase power in racing engines. Race parts are expensive, and they have to last. Most of us simply cannot afford to throw out a complete engine combo simply because a new one may produce a few more pounds of torque.
Clements Racing Engines builds engines for all levels of racing, but it specializes in high-end dirt Late Model racing. The company has an exclusive relationship with Dart to machine its small-block castings for circle track racing. Clements also has a complement of computer numerically controlled (CNC) milling machinery to produce amazingly consistent racing heads.
That is how the idea to produce its new 16-degree Chevrolet small-block head came about. In addition to using the CNC machinery to produce new heads, Glenn Clements, one of the three Clements brothers who make up Clements Racing Engines, also developed a process for using his CNC machines to angle mill a set of heads. Over time, Glenn slowly worked out a method to take a raw, 18-degree aluminum casting from Dart and produce a more efficient head based on 16-degree valve angles.
"We basically just took our 18-degree heads and rolled them over," Clements explains. "These castings from Dart have a lot of material left in them so there is plenty for us to work with as we moved the ports around and stuff. They clean up, but in some places just barely."
The difference between 18-degree heads and Clements' new 16-degree pieces (and even the older, but more common 23-degree Chevrolet heads) is the angle of the valve in relation to the deck of the head. Consider a line perpendicular to the deck of the head to be zero degrees. The line of intersection created by the valve stems (and the path the valve travels) is the measured angle. If the valve traveled in the same path of the piston, that would be a zero-degree head. The farther the valve is leaned over, the larger the number in degrees. Thus, the valves in the older 23-degree heads are leaned over the farthest.
Valves are angled in the cylinder heads to make it easier to build a compact engine package. Twenty-three-degree heads are easier to use with flatter intake manifolds. In racing, the engine's physical size is only a consideration if you aren't allowed to cut the hood. Racing heads with straighter valve angles tend to perform better than those with more extreme angles.
"Every engine builder will have his own theories about why things work in an engine," Clements explains. "But, it seems that when you stand the valves up, the engine seems to be able to pull in the air/fuel mixture better. Obviously, if you look at it from the aspect of the air moving into the cylinder, the majority of that work is done by the piston creating a low pressure area in the bore as it moves down and away from the valves. If the valve is leaned over, the air/fuel charge is going to have to bend more acutely to get lined up with the bore and fill the bore. When you stand the valve up, good things start happening. Now, the low-pressure area created by the piston seems to pull the air/fuel mixture from around the valve equally all the way around the valve seat, when before most of the flow was from the lower portion of the seat. It isn't shrouded as badly by the roof of the combustion chamber."
Of course, it's easy to get a pair of race heads machined at just about any valve angle. The problem comes because the change in angle requires an almost completely different engine. Changing heads with different angles almost always means you also have to change the intake manifold and exhaust headers. The new geometry involved can also mean new valves (if the head requires longer stems), pushrods, rocker arms, pistons, and springs. Often, that kind of change is cost-prohibitive.
Clements Racing designed its 16-degree racing heads to bolt right on an engine designed around the more conventional 18-degree head. By going with slightly longer intake runners, the heads maintain the standard angle on the intake face. Any intake manifold designed for an 18-degree Chevrolet will bolt right up. Mounting angles and bolt patterns also match up for exhaust headers and a shaft-mounted rocker arm system. Instead of having to order custom components, engine builders will have the selection of engine parts already designed by multiple manufacturers to work with the common 18-degree setup.
The only change likely to be necessary is a modification of the valve pockets in the pistons. Clements explains the change in angle is set on an axis about 2.5 inches from the dowel locators. This moved the valve centers slightly in the bore. If you are running a minimum valve clearance, you may need to move your valve pockets. They will not need to be any deeper, but moved a little more toward the back of the pocket. The best method for checking is to assemble the bare head on the block with the rotating assembly already in place and the piston you want to check at TDC. Use a punch that fits fairly snug in the valve guide. Extend the punch through the guide until it contacts the piston top, and make a small mark on the piston. This marks the center of the valve. You can now measure your valve size to determine if it will fit within the pocket at that location.
"All the standard 18-degree hardware fits," Glenn Clements says. "So, basically, if you wanted to upgrade a standard 18-degree motor, all you need is a set of heads. Perform a valve pocket modification on the pistons and bolt them on. If you're running a moderate amount of piston-to-valve clearance or large valve pockets, you may not even have to do that.
"We think these heads are probably best suited for the dirt Late Models and that type of market," Clements continues. "It makes a wide powerband and just makes good power overall. In terms of maximum power output, you might see more from an SB2 setup-we've raced them ourselves in the ARCA series. But the powerband isn't where you want it for most applications. Those cars (typically Winston Cup Chevrolets which run SB2 heads) stay in the really high-rpm ranges. In short-track racing, you need the power to come on lower and the powerband to be wider. You want the engine to be able to really pull out of the corners and get you going on restarts when the engine is really lugging around on low rpm. For that, we feel a 16-degree engine is a better option all the way around."
The Spec Sheet
What: 16-degree cylinder heads
For: Chevrolet small-block
Displacement Range: 358-414 cid (recommended)
Chamber Volume: 49 cc
Intake Runner Volume: 260 cc
(same cross-section as 18-degree head)
Valve Seats: 2.150-inch (intake), 1.600-inch (exhaust)
Valvetrain, gaskets, manifold, and headers: Anything available for Chevrolet 18-degree heads will fit.