The TR4 uses the same diffs and spurs as the Fun Factors so I wouldn't be to concerned about trying to upgrade them. If the diffs become a problem you can upgrade to the machined cross shaft FFS027. You should also be able to use the machined diff gears.

Yes brakes are important and on something that fast I highly recomend the metal brake disk GX38 and the metal brake plug.

The TR4 uses a slide carb so you will need the OS with the slide carb http://www2.towerhobbies.com/cgi-bin...&I=LXGGP6&P=ML


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