What, exactly, are straight cut gears?

Hear about them, no idea what benefit they are. :?

Well, straight cut gears are your typical "how things work" picture of gears. Most car gearbox gears are helical.

The difference: http://image.streetrodderweb.com/f/...ar_end+straight_cut_and_helical_cut_gears.jpg


Helical gears are quieter, but I think offer more friction than straight gears.

A lot of cars (not sure about the STI) have a straight-cut reverse gear. You can definitely hear the whine even at lower speeds.

I think the advantages of straight gears are a little extra power due to lowered friction, and I *think* there's a shifting benefit, but I cant really remember what that is. The downside is they're LOUD. Thats why you only ever really see them for reverse and race cars.

edit: I should also mention something about thrust loads. Helical gears end up putting a load not just tangential to the circumfrence of the gear (turning the gear) but along the gear's axis. More power-->more sideways loading-->more reinforcing=heavier.

Research PPG transmissions. They utilize straight cut gears in a lot of subaru transmissions.