TU's you are using are the original dual motor Tamiya Type 1's. They are pretty fast. The latest Type 3 for alll but the P4, or the Type 4 for P4, should give you much more room inside, and bring your speed down to scale.
Here's the etoarmour version of the Type 1's, set up for competition and just put on sight in a limited run. Will rummage up a photo of the Type 3's for you later today, but the Type 3 and 4 have the black plastic covers and much smaller, and more, gears.