The St170 box has 2 layshafts so it keeps the gears 1st, 2nd and 3rd normal spacing and then uses 4th, 5th and 6th as close ratio gears, not idea for a turbo powered car, i think a turbo works better when its got something to work against and a N/A just need to rev as fast and as high as possible hence the ST170 gearbox layout