That's a good running car there. The Losi 3.4 is okay as long as you don't add much power to them. The rod will let go fairly quick in them if you add a little timing and increase blow-down and other drag mods. They will absolutely scream but the rods are weak. He is a little OS .15 that I tweaked a little. I live in Denver (elevation is quite high) so the engine is down about 18-20 % up here.

https://www.youtube.com/watch?v=zFfJ_CDspXs