[AaronM]

Originally Posted by 962porsche

they are loud because they have what are called straight cut gears in them . the gears in your street trans has the gears cut on a angle . but by doing so you can't shift with out using a clutch.

Actually, it's perfectly possible to shift a transmission with helical gears without using a clutch. You simply have to rev-match near-perfectly. However, the synchros and blocker rings make it exceptionally difficult and place great strain on the shift forks, so it is not recommended. This is because the synchro mechanism actually incorporates a blocker to physically prevent the dog teeth from engaging unless their speeds are synchronized. However, there are lots of non-synchro transmissions with helical cut gears (OTR semis and motorcycles come readily to mind) where shifting without a clutch is the regular mode of operation even with helical gears.

Originally Posted by cockerpunk

false

the helical gears of a standard transmission do not engage and disengage when the shifter is moved, or the clutch is used. the helical gears always remain in contact for all gears at all times. the shifter connects and disconnects the syncros, not the gears themselves.

Synchros do not "connect" or "disconnect." They merely provide an amount of friction force to allow the dog teeth to engage smoothly. The synchros themselves have absolutely nothing whatsoever to do with coupling the gears to their respective shafts; all the synchros do is smooth the engagement of the dog teeth. Most synchro systems also employ some form of blocker to prevent contact between the dog teeth until the synchros have done their job and matched the rotational speeds.

On a general note, helical-cut gears are physically stronger than straight-cut gears as well as quieter. The benefit of straight-cut gears is that they allow "crash box" transmissions (transmissions where the shifting is done by engaging the gears themselves and not by engaging and disengaging dog teeth) and they are cheaper and easier to manufacture. When dealing with a racing transmission that is less likely to be expected to last 200,000+ miles and where the ability to use custom-cut ratios for different tracks is important, straight-cut gears have an advantage.

Originally Posted by Chunkerz

Not having to rev match when I downshift seems like a godsend to me.

You still have to rev-match on a downshift with a sequential transmission unless you want to jerk the ever-loving ***** out of the car when you re-engage the clutch. Rev-matching is NOT the same as double-clutching; rev-matching means that you bring the engine close to the right RPM before re-engaging the clutch after a shift has been completed. This is necessary for smooth driving regardless of whether you have a sequential gearbox or a standard H-pattern box. While a sequential gearbox will eliminate double clutching between gears, it will NOT remove the need to rev-match to make a smooth downshift (any motorcycle rider can tell you this).