Killing the Buzz - Installing "Even Running" Cam?

[the Ferret]

I've never ridden an I-4 that was turbine smooth at all rpms

opposed 4 yes

inline 6 yes

but not an I-4

Not sure it could be done without mechanical trickery. An I=4, although balanced in the primary phase, is not inherently balanced in the secondary phase, therefore causing vibrations

From Wiki

Balance and smoothness

The inline-four engine is much smoother than one- or two-cylinder engines, and this has resulted in it becoming the engine of choice for most economy cars for many years. Its prominent advantage is the lack of rocking vibration, and the lack of need for heavy counterweights makes it easier to be sporty (quick revving up and down). However, it tends to show secondary imbalance at high rpm because two pistons always move together, making the imbalance twice as strong as other configurations without them.