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Mass-produced#2 in family

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Top-tier supplier movement · caliber IWC Cal. 79320: Valjoux 7750 base, IWC-decorated, 28,800bph, 44h PR, 25j; used in Portofino Chrono and Pilot Chrono 3777 · 44h power reserve
Medium-large: suits wrists 6.5 in+ (16.5 cm+)
42 mm case. Wears confidently on average to larger wrists. May overhang on slender builds.

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Authentication

Verify the IWC-signed rotor and IWC movement finishing through the caseback; a generic ETA 7750 without IWC decoration indicates a movement swap.

Known issues in the market
  • Cal. 79320 is an IWC-modified Valjoux 7750; the movement must show IWC decoration and signing to confirm authenticity.
  • The cam-operated chronograph architecture (not column-wheel) is normal for this caliber.
AreaWhat to checkWhat is correctRed flag
casebackIWC-signed rotor and Cal. 79320 movement finishingIWC-signed rotor visible through caseback; IWC movement finishing and decoration on bridges; Cal. 79320 identity confirmedGeneric ETA 7750 without IWC signing or decoration; unsigned rotor; no IWC-specific finishing
dialPortofino dress chronograph dial layoutClean dress-oriented dial with 3-register chronograph layout; Portofino case proportions appropriate for this movementDial layout inconsistent with Portofino specifications; any non-standard sub-register configuration
casePortofino round case with pushersClean round Portofino case; both chronograph pushers operating cleanly with no bindingEither pusher binding or sticking; case shape inconsistent with Portofino line
Common legitimate replacements
  • Original IWC Portofino strap; factory replacements are standard.
Expert resources: IWC Portofino Chronograph product documentation. IWC Cal. 79320 specifications.

Authentication guide

Last reviewed June 2026

The IW391036 is a 42mm Portofino Chronograph with a Cal. 89361 (in-house flyback chronograph). The Portofino family targets the dress watch segment; thin case, slim lugs, and a silver or white dial are the identifying characteristics. The flyback complication distinguishes this from the standard push-button chronograph found in many competitors.

Known reproduction risks

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MEDIUM

Replica Portofino Chronographs using ETA-based movements

  • The flyback function is the fastest test: a standard cam-based chronograph will need two pusher presses (stop, then reset) rather than one flyback action
  • Exhibition caseback on replicas often shows an ETA 7750 layout with the visible auxiliary seconds register position different from the genuine Cal. 89361
  • Roman numeral quality on replicas is often uneven under magnification

Dial variants by era

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EraDescriptionIdentifiers
2014 to presentSilver dial with three-register chronograph. Applied gold-tone Roman numerals. Blued steel hands. The flyback function allows the chronograph to be reset and restarted in a single pusher action.
  • Roman numeral chapter ring (I through XII)
  • Three-register chronograph at 12 (12-hour), 3 (date), 6 (30-minute), 9 (small seconds)
  • Date in a subdial at 3 rather than a date window
  • "PORTOFINO CHRONOGRAPH" text above 6 o'clock
  • Flyback operation: hold the lower pusher to reset and restart simultaneously

Service part flags

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Movement

Original: Cal. 89361 is an IWC in-house flyback chronograph caliber. It is not ETA-derived and has a column-wheel mechanism with the flyback return spring.

Replacement tells
  • Any ETA 7750-based movement in a stated IW391036; the in-house caliber is visually distinct
  • Chronograph that operates as a standard push-reset rather than flyback; press lower pusher once during a running chronograph and observe whether it resets and restarts in one action

Case back markings

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2014 to present
  • Exhibition caseback showing Cal. 89361
  • Engraved ring on the caseback: IWC SCHAFFHAUSEN with reference IW391036 and serial
  • No soft iron cage (Portofino is not an anti-magnetic Pilot reference)

Movement tells

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  • Cal. 89361 runs at 28,800 bph with approximately 68 hours of power reserve. The flyback function should operate cleanly with no hesitation on reset.
  • The column wheel is visible through the exhibition caseback; it rotates one step per chronograph pusher action. A cam-based mechanism visible here indicates a non-original movement.
Sources: IWC Portofino product page; WatchUSeek -- Portofino Chrono IW391036 thread.

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