It's the Diamondback Momentum, no doubt. In the first couple of "transition years," DB kept the name Centurion on the top tube, probably to try and hold onto some name recognition. If I was trying to follow up the successful 4-year run of Ironman and Lemans models, I would, too.

Often, there was also an Avenir logo back near the seat tube, I guess in exchange for a deal on the Avenir saddles they used, which almost all were covered in cloth that didn't last very well. As production costs increased, component levels pretty much decreased to maintain a price point.

There was a Diamondback Master and a Diamondback Expert offered, probably to try and keep some of the interest from the earlier Ironman Master and Ironman Expert. Some were lugged, probably only the 1990 or maybe 1991 models, most were not. It appears the DB Master and Expert were close to the Centurion Lemans and Lemans RS. I think the DB Master and Expert evolved into the Master TG and the Expert TG, which were TIG-welded. I had a nice 58cm Expert TG wtih compact triple RSX and Matrix wheels, a nice setup and pretty light, too. The tubing was simply labeledl "100% Chrome-Moly" by then. Seems the tubing decals changed every year around that time.

The Interval and Momentum were not that far apart in component levels, but the Momentum was probably lighter, as the Interval, I believe, was either HiTen tubing or something suitably in that weight range.

Some of the Centurion paint schemes carried forward, as in sjpitt's example above of the marbled treatment, also found on '89 Ironman models. Also offered were some "speckled" paint schemes, much like the early PDG Paramounts.

DB was in the process of putting all their eggs in the MTB market at the time, and not many steel bikes made it through the early 90's without taking real hits, for a variety of reasons.