The 12A engine has a long thin shaped combustion chamber, having a large surface area in relation to its volume. Therefore, combustion is cool, giving few oxides of nitrogen. However, the combustion is also incomplete, so there are large amounts of partly burned hydrocarbons and carbon monoxide. The exhaust is hot enough for combustion of these to continue into the exhaust. An engine driven pump supplies air into the exhaust to complete the burn of these chemicals. This is done in the "thermal reactor" chamber where the exhaust manifold would normally be on a conventional engine. Under certain conditions the pump injects air into the thermal reactor and at other times air is pumped through injectors into the exhaust ports. This fresh air is needed for more efficient and cleaner burning of the air/fuel mixture.[2]
Options and models varied from country to country. The gauge layout and interior styling in the Series 3 was only changed for North American versions. Additionally, North America was the only market to have offered the first generation RX-7 with the fuel injected 13B, model GSL-SE. A turbocharged (but non-intercooled) 12A engine was available for the top-end model of Series 3 in Japan.
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