No nitro offroad buggy or truggy is going to keep up with a brushless Revo in a straight line race (if it is running balls out on 6s) unless you build your own brushless truggy or buggy. It won't happen with a nitro under any circumstances no matter how much you spend or who mods the engine.
Your only hope is a nitro touring car but that really isn't an apples to apples race at that point.