GEARS ARE NOT THERE TO CONTROL THE "ENGINE VOLUME", brother... They're there to reduce engine rpms at any given speed.
Thing is: MORE RPMS = MORE WEAR & DAMAGE.
Just keep the RPM's low, not the GEARS and/or SPEED...
Going 60km/h @ 4,000rpm in 4th gear is actually BETTER than going 40km/h @ 5,000rpm in 3rd gear.
So do "SHORT SHIFTING" on your new engine.
Hope it clears any confusion.