Why so many IWC chronographs ran a 7750
For decades the Valjoux 7750 was the dominant Swiss automatic chronograph: robust, easy to service, available to anyone who paid ETA. IWC, like Breitling, TAG Heuer, Tudor, and many others, built the bulk of its chronograph catalogue on this base from the 1980s through the late 2000s. The Cal. 79320 is IWC's in-house designation for the 7750 with IWC modifications: refinishing, custom rotor, sometimes regulator changes, and IWC service certification.
The Pilot Chronograph era
The single most-recognised use of the 79320 is the IWC Pilot's Watch Chronograph ref. 3717 (2006-2016), the 42 mm steel chrono with the iconic black dial, white luminous numerals, and the day-and-date double window at 3 o'clock (a 7750 dial signature: the day-date wheel arrangement). The same caliber powered the Top Gun Chronograph ceramic versions, the Spitfire Chronograph, the Aquatimer Chronograph 376705, and the Portuguese Chronograph variants in steel. Across these references the 79320 (and its sister variants 79350, 79430, etc.) is essentially the same Valjoux 7750 inside.
How IWC modified the 7750
IWC's changes were largely cosmetic and finishing: a custom rotor with Probus Scafusia engraving (or model-specific designs), refined plate decoration in some applications, and IWC's own quality control. Mechanically the architecture stays the 7750: cam-actuated chrono, lateral clutch, 28,800 vph, 44 h reserve, day-date displays, tri-compax layout. The reliability of the 7750 is one of the reasons IWC chose to base its mainstream chronos on it rather than develop in-house earlier; the architecture has been proven over millions of units across the industry since 1973.
Replaced by the in-house 89000 family
Starting in 2007 IWC introduced the Cal. 89000 family in-house, with central minute and seconds chronograph display, column-wheel, flyback, and 68 h reserve. The 89000 progressively took over the higher tiers of IWC chronographs: Da Vinci Chronograph, Portuguese Chronograph Classic, Big Pilot Chrono. By the late 2010s the 79320 was being phased out across the catalogue; the current Pilot Chronograph 3777 introduced in 2016 still uses a 79320-family movement, but the Pilot Chronograph 3878 (2021) uses the in-house Cal. 69380.
Service and value
A 79320 is fully serviceable at any independent watchmaker familiar with the Valjoux 7750: parts are completely interchangeable with the standard ETA 7750, prices for service are USD 400-700 at an independent. IWC service runs higher (USD 700-1,000) but includes a refresh of finishing and IWC certification. Used IWC Pilot Chronograph 3717 with the 79320 trades on the secondary market at USD 3,500-5,500, well below current new-Pilot prices.