Engine Maintenance and Modification Bradley Artigue

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FIAT 124 Spider Engine Maintenance + Modification 8. Exhaust System The exhaust system conveys spent gasses from the cylinder head to the exterior of the car. Exhausts perform a number of valuable functions and exhaust design is crucial to good engine performance. Emissions, noise, and backpressure are key concerns in exhaust design. Emissions must be safely conveyed away from the passenger compartment; in the case of the FIAT Spider they are reduced by a catalyst and expelled behind the vehicle. Noise produced by an engine must be muffled in order for the vehicle to function in society; therefore a muffler is installed at the rear of the vehicle to reduce exhaust noise. Spiders also have a center resonator, an additional muffling device located above the rear axle. Backpressure exists if gasses escaping the engine meet resistance and, taking into account the safety and environmental features noted above, is the focus of good exhaust system design. A poorly-designed exhaust manifold may create pressures that inhibit the engine’s ability to breathe. Many vehicles have intricate exhaust systems, designed specifically to equalize the length of each cylinder’s exhaust pipe. FIAT Spiders used two types, known as 4-2-1 and 4-1; the former is considered to be a superior design. Aftermarket headers are also produced, each touting improvements to the original designs (with dubious pedigree; refer to the section titled “improvements” later in this book.) There are two types of the 4-2-1 design. The first was fitted to 1756cc Spiders manufactured in 1974. There are four pipes running from the exhaust side of the engine, tapering down to where a flanged two-pipe fitting mates and extends under the car. Here a single pipe leads through a catalytic converter (or not, depending on year), through mufflers and out of the car. The second type of 4-2-1 was installed on the fuel injected Spiders. It is similar in design except the four primary pipes bend into two and into a collection “box” where the oxygen sensor is installed. The 4-2-1 was designed for Spider engines in the 100+ HP range and is at least as good (arguably better) as most “performance” aftermarket systems. The 4-1 design was installed on most Spiders and in every engine displacement. Four short pipes extend from the exhaust manifold into a single pipe that runs under the car to the catalyst and onwards. The design is simple and the exhausts are very well built. They suffer only from the rather abrupt turns from the exhaust ports to the down pipe and, unless the engine is going to produce more power than stock, may not be worth replacing. 8.1 Exhaust System Identification Look in your engine compartment at the exhaust side of the engine. There may be a metal heat shield on top of the exhaust - it will have three 13mm nuts securing it down. The exhaust system parts have the part numbers stamped into them. It is very unlikely that a Spider will have the original parts from the down pipe back. 64
FIAT 124 Spider Engine Maintenance + Modification Table 8: Exhaust System Casting Numbers Year Manifold Header Pipe Intermediate Muffler Rear Muffler Note 1967 4151276 4310530 4401843 4285627 1968 4151276 4310530 4401843 4285627 1969 4151276 4310530 4401843 4285627 1970 4151276 4310530 4401843 4285627 1971 4151276 4310530 4401843 4285627 1438cc 1971 4166429 4310530 4401843 4285627 1608cc 1972 4166429 4310530 4401843 4285627 1592cc 1973 4166429 4310530 4401843 4285627 1974 4308891 4310530 4401843 4285627 1975 4314919 4341428 4341867 4285627 California 1976 4314919 4341428 4341867 4285627 1977 4380776 4341428 4341867 4285627 1978 4377811 4341428 4341867 4285627 1979 4407872 4419699 4419683 5976218 1980 4407872 4419699 4419683 5976218 1980 4462282 4443328 4443325 5976128 California 1981-1985 4462282 4443328 4443325 5976128 To Chassis 5506060 1981-1985 4462282 7531187 4443325 5976128 From Chassis 5506061 65
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Engine Maintenance and Modification
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