If you are serious about racing you must have straight cut gears. The primary benefit comes from the ratios availability; anytime you can keep the engine in the real torque curve, you've won the race!
The stock helical "S" box has a first gear ratio of 3.2:1, second gear 1.916, third 1.357. The "S" 3 sync close ratio kit has a first gear of 2.573:1, second 1.722 and third 1.255; these numbers mean closer ratios to keep you in the torque range. For use in B type boxes ONLY. B type boxes have needle rollers on 2nd/3rd gears, A type has bushes.