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Updated 17/03/00 Type BPD Engine
The Mazda 323 4WD GT-R is powered by an evolution version of the turbocharged and intercooled, type BPD, twin-overhead-camshaft, 16 valve, 1,839-cc, inline 4-cylinder engine. This power plant has been specifically developed for the GT-R and will serve as the basis for the unit for the forthcoming Group-A engine. The GT-R's type BPD engine has been developed by Mazda's Motor Sports Engineering Group. The type BPD "Big Turbo" produces 136kw EEC (139 kw DIN) at 5,000 rpm and a maximum torque of 235Nm EEC (240 Nm DIN) at 4,500 rpm, figures which are 13 and 8 percent higher, respectively, than the output of the type BPD Turbo that powers the 323 4WD GT-X. The engine's strengths, both power output and torque characteristics, are in the mid-through-high-rpm zone, above 3,000 rpm up to its maximum allowable 6,500 revs. Numerous improvements have been carried out inn the engine's internals, and the new "Big Turbo" and larger and more direct intercooler system is adopted in the GT-R unit. The evolution version of the Type BPD, DOHC, 16-valve, EGI/Turbocharged Engine The type BPD DOHC engine has an 83.0mm bore and an 85.0mm stroke for a total cubic capacity of 1,839 cc. The compression is 8.2:1 and the engine requires premium grade unleaded fuel (minimum RON 95). The cylinder head is precision diecast aluminium, carrying twin overhead camshafts. The single-stage, cogged-belt-driven camshafts operate 4 valves per cylinder via inverted bucket tappets that incorporate hydraulic lash adjusters, which maintain precise clearance without periodic adjustment. The camshafts are hollow-cast to reduce weight, each camshaft being 500 grams lighter than a comparable solid camshaft. The valves are Vee-inclined at an included angle of 50 degrees in a compact pentroof combustion chamber with squish area. The spark plug is centrally located in the combustion chamber. Valve diameters are 33mm (intake) and 28mm (exhaust) having 8.00mm and 8.5mm lifts respectively. The exhaust valves are sodium cooled. Encased within each thin, hollow, 6-mm valve stem is metallic sodium, which when exposed to heat, liquefies and helps dissipate heat from the head of the valve. The aluminium pistons are squeeze-cast with a cast-in cooling channel. With this technique, molten metal continues to be pressurized while it cools in the mold. Blow-holes that might otherwise form during cooling contraction are driven out by pressure, and a denser, stronger casting is formed. Further, the pistons top ring groove area is reinforced with integrally cast nickel-based "metal foam". The nickel foam is produced by electroplating urethane foam, which is then melted away, leaving porous metal "foam". The foam ring is integrally cast in the piston by the squeeze-casting method. The metal reinforced, squeezed-cast piston with cooling channel was first adopted in Mazda's direct-injection diesel engine, whose pistons are subjected to extremely high thermal load during the combustion process. the metal reinforced piston is about 10 percent lighter as compared with an aluminium piston with Niresist top ring groove, and according to Mazda's testing has an extended piston life by threefold. The piston's skirt is also zinc-plated for improved wear resistance, and its inside is cooled by an oil jet. The forged steel connecting rods have a larger section for added strength. The connecting rod's big-end bearing is fully balanced with counter weights and is supported by five main bearings, again of competition grade kalmet metal. Manifold System With the "Big Turbo", it has become critical that boosted air is distributed to the individual cylinders in equal volume and pressure. Likewise, the energy of exhaust gas must be fully exploited to quickly "spin-up" the big turbine in order to obtain high power and minimum turbo lag. The Mazda engine design team has perfected a unique manifold system, combining the air volume and pressure equalizing intake and exhaust extractor manifolds. It was Mazda's finding that with more a more commonly used equal-length intake manifold, the tract nearest to the air entry received the least volume/pressure, and the farthest tract the most. By trial, measurement and testing, the engine team perfected a cast aluminium manifold that has intricately curved and sized "walls" between the individual tracts leading to the intake ports to equalize air volume and pressure. A bonus is that the manifold's swirl generating effect contribute to efficient combustion. The equalizer intake manifolds have shown its effectiveness in improving torque from idling to the Group-A 300-bhp-plus output level and all the way up to maximum revs. The exhaust manifold has individual tracts collecting at the turbocharger entry. These tracts are in two groups; the tracts from cylinders 1 and 4 are routed to the center, and those from cylinders 2 and 3 to the outside. This routing allows nearly equal tract length. The complex manifold is made of cast ferrite steel, for which the lost-form casting method is employed. Not only is this about 20 percent lighter, much stronger and its passages much smoother than a conventional cast iron one, but also its surface finish is much smoother. The exhaust manifold's extracting ability precludes an unwanted rise in exhaust back-pressure, which would cause the dilution of the combustion chambers with exhaust gas. This would, in turn, raise cylinder temperatures. Enriching the fuel/air mixture to lower combustion temperatures would obviously deteriorate fuel economy. The GT-R exhaust system adopts a 3-way catalytic converter with larger capacity but a reduced number of cells, and a new main silencer that assures reduced resistance to gas flow. Source:Product Information Mazda 323 4WD GT-R ; Mazda
Source:Product Information Mazda 323 4WD GT-R ; Mazda |
