Just remember that rollers aren't always perfectly accurate and that 158bhp car may have been an isolated example, all factory standard engines give different power output from car to car so in reality you could have anything between 145 up to 160ish BHP, it might be that some are luckier than other when getting their ST, also it might have something to do with the way the car is run in when first driven!
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Up the
Boys/Girls!!!