Only the very best high end .21 engines will come close to the Losi 454 in power. I wouldn’t replace a Losi 454 with an Axe Rossi engine - Axe engines are okay... but not great. Now if you wanted to compare apples to apples, try a Novarossi Truggy 28-8 in place of the Losi 454. Same displacement, easy to set up, and gobs more power.