The fake IW371670 question usually comes in two versions. One is whether a replica of this reference can pass a hands-on look. The other is whether the watch in a specific listing is real. Short answer to the first: no. The Portugieser Chronograph is copied a lot, and the copies are good at arm's length, but they fall apart under a loupe, on a scale, and with the caseback off. Short answer to the second: verify the reference string before anything else, because IW371670 is not a number most dealers can place from memory, and that is exactly why fakes get listed under it.
Start with the reference itself
IWC prints the reference on the caseback and repeats it on the warranty card. On a genuine watch those two agree, digit for digit, and the serial on the card matches the movement and the caseback. Ask the seller for clear photos of both. If the number on the card is a different format, or the listing photo is too soft to read the engraving, stop there. Then confirm the sub-reference exists with that dial and case combination on IWC's own reference material. A seller who cannot show the number in both places is not a seller worth arguing with.
Case and crystal
The Portugieser Chronograph is a 41mm watch, and the genuine case sits around 13mm tall. Replicas built on a Valjoux-type movement need a spacer, so the case runs a millimeter or more thicker and the caseback sits proud of the wrist. Put it on a caliper if you can. Look at the lugs too: real ones have a crisp polished bevel line where the brushed flank meets the polished top. Copies round that edge off.
Fake IW371670 Compared to the Real IWC: Which Replica Wins
The crystal is the fastest tell in person. Genuine anti-reflective coating is close to invisible. Replicas show a blue or purple cast at an angle, sometimes a haze across the dial.
Dial, hands, and date
- Subdial rings at 12 and 6 should be sharp under a loupe. Copy printing feathers at the edges.
- Applied numerals on the real watch have polished, knife-edge facets. Fakes look slightly soft and thicker from the side.
- The date aperture should be cut clean and the font weight should match the rest of the printing. Misaligned or oversized dates are common on replicas.
- Hands should be flat and flawless. Look for burrs on the chrono seconds hand at the counterweight.
Movement and pushers
Genuine examples of this line run an in-house chronograph calibre with a column wheel. Start and stop feels crisp, with a short, clean take-up. A 7750-based copy feels spongy and the reset snaps harder. With the caseback off, real bridges carry proper decoration and the rotor engraving is sharp and evenly filled. Copies show stamped lettering, rough perlage, and a rotor that just looks flat.
Price and paperwork sanity check
Genuine secondary market examples trade in the mid four figures to low five figures depending on age and configuration. If a watch sold as genuine is priced near replica money, it is a replica. Boxes and papers are easy to fake, so treat them as a bonus, not proof. Ask for a return window and get a watchmaker to open the back within it. That single step answers the fake IW371670 question better than any photo.