I have just completed building the E maxx of my dreams. I'm still in the process of upgrading the remaining plastic parts to aluminum, but I have most of the go fast goodies in place.
I started out with a Dynamite chassis that will hold 4 battery packs. I felt the need for this since Dual Hv Maxx motors would be supplying the power. Dual Escs with motors spinning upwards of 70,000 rpms is enough to present the challenge of getting all this power to the ground without breaking parts.
For gearing, I'm using the 21 tooth pinions and a 64 tooth spur with all 12 friction pegs installed. Then I cranked her down to allow only minimal slippage at the clutch.
All of this grants an estimated top speed of around 60 mph. But I have to work the bugs out first.
Tire Balance and Swelling. It's amazing how these soft tires react to being spun this fast. I need a way to balance tires, and maybe look toward some harder compound that doesn't swell so much. These soft ones totally distort!
Bullet Proof Differentials! Second time out, I sheared the Ring screws. I haven't even tore it back down yet. I heard them snap with a loud Pop! Then all the sudden, I had a front wheel drive E maxx that would smoke the tires on concrete! LOL
I have the Purple aluminum diff cases. I have just ordered the aluminum diff cup, hard gears, and the 3 mm screw setup to rebuild this diff with.
Putting this much torque to the ground is really going to punish the diffs.
Can you guys give me some good cost effective advice on how to build diffs that will hold up?

This thing accelerates like crazy! I did manage a few second gear high speed runs before the diff broke. It's going to top out over 50mph. I need to come up with a way to verify that. I wouldn't mind putting this thing up against a tricked out T maxx. A stock T maxx wouldn't stand a chance! hehehhee

Take a look at these pics! Let me know what you guys think!