So was his time faster than usain bolt?
His time was 9.79 s which was not bettered until Tim Montgomery ran a 9.78 a little over 14 years later, which is an amazingly long stretch for a sprint record. Montgomery's record was later disqualified because he was a juicer too (as if they all aren't, haha). It wasn't until 2005 that someone beat Johnson's 1988 time and wasn't caught for using PED (or hasn't been yet; Asafa Powell).
Johnson's time in 1987 when he first set the record was 9.83 s, which beat the existing world record by 0.10 s. That's an incredible margin in a race that short. It was almost the same margin as what Bolt did with his 9.58, although he was beating his own existing record. In the course of a year Bolt improved the record by 0.16 s and if anyone approaches that for the next 15 years or so I'd be stunned.