Invulnerability on startup frames of E. Honda's jab Headbutt in Super Street Fighter 4 and applications - Super Street Fighter 4 Note - sf4answers

Honda now has invulnerability on the startup frames of his jab Headbutt in Super Street Fighter 4:

This is a change from vanilla, where he didn't have invulnerability on his Headbutts.

As for just how many frames of invulnerability he has, that's hard to say, given there is no good frame data for Ryu's projectiles/hitboxes (the frame data is about his movements, not the projectile's).

However, as the video shows, it's enough to go through one of his regular Hadokens (although it's difficult to tell which one from the video) as well as the EX Hadokens (which is faster).

That being the case, Honda should have enough invulnerability frames on the startup of the Headbutt to go through Guile and Seth's Sonic Booms, as they are some of the faster (if not the fastest) projectiles in the game.  That would also extend to the EX versions as well.

Beyond going through fireballs, the massive advantage that Honda has regained all of the anti-air and wake-up uses that he had for the jab Headbutt in Super Turbo/HDR, the two main ones being as an anti-air as an option on wake-up.

In Super Street Fighter 4, the use of a jab Headbutt as a wake-up option is even more useful as it can be used to thwart an opponent trying to throw you on wake-up, in addition to using it against opponents that are jumping in on you on wake-up.