Let me see if I can shed some light on your question concerning straight cut, verses helical cut gears and dog engagement, verses synchromesh engagement.
First of all, these are separate, but related topics.
Straight cut gears have teeth that are cut straight across the gear blank, or parallel to the rotational axis. Helical gears are cut at a slight angle to the rotational axis.
The advantage of straight cut gears is they tend to be stronger, which is a good thing, especially for racing purposes. The down side is, straight cut gears tend to be noisy, which is generally a problem for road cars. Helical gears generally have more than one tooth pair in contact at any given time, which presumably results in a quieter gear system.
My understanding is dog, verses synchromesh engagement, are different methods for spinning up the gears to be meshed, during the gear change. Synchromesh relies upon hydrodynamic and friction forces to match rotational speeds, to facilitate tooth engagement.
It is also my understanding that dog engagement uses coarse teeth on the side of gears to spin them up to mesh the normal teeth. I believe motorcycle gear boxes are designed this way.
Synchromesh boxes are quieter and relatively more refined for street use. They are probably slower to engage however. Dog engagement happens quicker, but use of the clutch is not as critical. In fact, dog engagement minimizes the necessity of a clutch. The important thing is to back off the power delivery during the gear change for long life. This was quite normal on the motorcycles I rode as a young lad. Dog engagement is normally accompanied by a clunk, when changing gears, which is quite normal.
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With dog engagement there is no mechanism for rotational speed matching other than driver timing when changing up and that plus double clutching skill when changing down.
Elan +2S (1971)
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