Someone put up a small
guide to the engine ancillaries
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The BAM engine is 1.8L (1781cc) with a KKK turbo 'K04' producing approx 225PS or 222BHP. It has a four cylinders and 20 valves (5 valves per cylinder, 2 intake, 3 exhaust).
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A stage 1 remap from the likes of Custom-Code will produce about 275PS or 272BHP but usually requires changing the diverter valve, which doesn't like the increased boost. The stock valve is a Bosch unit which most people change to a Forge 007P with yellow spring.
Also worth changing is the paper air filter to a lightly oiled cotton gauze such as Jetex or Green. Nothing else really needs to be changed unless you intend to move to stage 2 where a front mounted intercooler and stronger turbo inlet pipes might be required along with a faster flowing exhaust from the likes of milltek.
Most of this can be found using the search on this forum.