I think there might be some threads on NASIOC, but my experience so far has been working directly with a shop.
The two variables when it comes to building up a 5 speed is convenience (both in terms of noise and engagement) and power level. Your options will deal with with either the engagement style (synchro or dogbox) and tooth profile (helical and straight cut).
You can work with a reputable shop to build a transmission that will meet your exact needs. Here is the my stab at weakest to strongest combo in terms of engagement and tooth profile, 1 being the strongest, and 4 being the weakest.
1. SC dogbox: dog gears are larger than gears with synchros, and SC will have larger tooth than helical. If you drive correctly, you’ll never have to worry about replacing synchros. If you don’t drive correctly, you will wear out the dog rings. LOUD.
2. Helical dogbox: quieter than SC, same rules apply with the dog rings.
3. SC synchro: engages like stock, stronger gears
4. Helical synchro: most stock like but stronger
The quietest and easiest (subjective) will be a synchro engagement helical tooth. You can get creative with the tooth profile (i.e. SC 1-2, helical 3-4) with any engagement.
As for diffs, the only player for center is an ASD unit with different level engagement (12k and 20k). For the front, CUSCO makes a few models. I went with 12k center and the CUSCO 1.5.
With a dogbox SC transmission with ASD center and CUSCO front, it should be good for about 800whp (or whatever the associated torque rating at that power). I went with this setup, with 5th gear being helical vs SC.
I personally enjoy driving the dogbox SC as a daily, and did so for 3 years through DC beltway. The noise however was super loud so I wore some noise reducing headphones.
After 30k miles of city driving, my dog rings showed no signs of wear (I’ve only briefly “bounced” my rings once).
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