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)
Material:Aluminum
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.