Over 15 years ago, Barney Navarro produced his Hi-Dome high performance cylinder heads for the Ford flathead V8. These heads have the area above the piston shaped the same as the early Chrysler hemi pistons.
A ball or sphere reduces the surface area to the smallest unit of volume. These heads are not a pop-up design and the piston does not extend into a cavity that blocks the transfer area. Instead, the shape forces all of the charge into the combustion area over the valves and promotes turbulence. As the piston moves down in the cylinder, the transfer area is opened immediately.
When looking at the photo of the interior of the Navarro high dome head castings (at right), you will note the bracing which is available on no other similar product.
This design, along with the pad over the exhaust valve allows for good compression along with excellent breathing characteristics. These features along with larger valves, radiusing the combustion chamber walls behind the intake valves and filling a portion of the valve bowl, produces over 30% more airflow and a similar resultant gain in horsepower. A 2-pattern cam should be used with these heads since the 1 1/2 exhaust valve doesnt have to open 7/16 to 1/2 like big intake valves.
Since this combination requires a special order set of pistons, the total package is not cheap.However, building a hot flathead is not an inexpensive proposition to begin with and compared with the total cost, this package is in line with other components. This is not an area to skimp on if you are really serious about the results.