page_title: Hemispherical combustion chamber
section_title: Ford
hierarchical_section_title: Hemispherical combustion chamber / Use / Ford
caption_attribution_description: English: Lotus Big Valve Head Hemi Chambers
context_page_description: A hemispherical combustion chamber is a type of combustion chamber in a reciprocating internal combustion engine with a domed cylinder head. An engine featuring this type of hemispherical chamber is known as a hemi engine.
context_section_description: Ardun heads for the Ford flathead were perhaps the first use of a hemispherical head on a readily available American V8. First offered in 1947 as an aftermarket product, these heads converted the Ford flathead to overhead valves operating in a hemispherical chamber. Zora Arkus-Duntov, who later worked for GM and was a major force behind the development of the Chevrolet Corvette, and his brother Yura, were the "AR" "DUN" of "Ardun."
  Ford produced an engine with two overhead cams (one cam per head) and hemispherical chambers in the mid-1960s. The engine, displacing 425 cubic inches and belonging to the FE family of Ford engines, was known as the "427 SOHC"; it was also known as the Cammer. It was a set of SOHC hemi heads that bolted onto Ford's FE engine block. The 1964 engine was designed in 90 days of intensive engineering effort for use in racing. The 427 SOHC used the side oiler engine block modified slightly to deal with the missing in-block cam among other OHC issues. Because of their power levels, and the fact that Chrysler had showed Bill France that a DOHC 426 Hemi was in the works, it was banned from NASCAR races, though allowed in certain drag racing classes. After the NASCAR ban, Ford continued to produce the SOHC, selling it over the counter to racers and others who used it to power many altered-wheelbase A/FX Mustangs and supercharged Top Fuel dragsters. Connie Kalitta, Pete Robinson, and "Snake" Prudhomme all used the engine in their Top Fuel racers. In 1967 Connie Kalitta's SOHC-powered "Bounty Hunter" won Top Fuel honors at AHRA, NHRA and NASCAR winter meets, becoming the only "triple crown" winner in drag racing history. Dynamometer results of the day showed the SOHC Hemi producing almost 700 hp (522 kW) in crate form (100 hp per liter). The overhead cams meant that it was not as rpm-limited as the Chrysler Hemis were with their pushrods and heavy and complex valvetrains.
  Later Ford engine designs with hemispherical chambers included the Calliope, which used two in-block cams, arranged one over the other, to drive 3 valves per hemispherical chamber. The pushrods activating the valves from the top camshaft were almost horizontal. In 1968, Ford brought out a completely new engine family called the 385-series. This engine's heads used a modified form of the hemispherical chamber called Semi-Hemi.
  In the 1970s, Ford designed and produced a small-block engine with hemispherical heads to address the growing concerns about fuel economy. Unfortunately, even with an ahead-of-its-time direct fuel injection system feeding a stratified charge chamber, the hemi's emissions could not be made clean enough for compliance with regulations. This plus the cost of the valve actuation systems, along with the cost of the high pressure pump needed to deliver fuel directly into the chamber, as well as the gilmer belt drive system needed to drive the pump, made further development pointless at the time. Most 1980s 4-cylinder Fords used the Ford CVH engine, CVH meaning "Compound Valve, Hemispherical (Head)".
caption: Lotus "big valve" head with hemispheric chambers
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