A fake IW371663 is a counterfeit copy of an IWC Portugieser Chronograph, sold with the reference number of the genuine watch attached to it. The number identifies the real piece, not the copy, so any listing carrying it can be either an authentic watch or a replica wearing the same digits. Sorting one from the other comes down to four things: the movement inside, the dial layout, the case finishing, and the paperwork that ties the serial number to the reference.
This guide explains what the reference covers, why the exact string gets searched, and which checks expose a copy before money changes hands.
What the IW371663 reference points to
IWC builds its reference numbers from the letters IW followed by a digit block. The Portugieser Chronograph family sits in the 3716 block, which shows up as references such as IW371604, IW371606 and IW371617. The digits after the block mark dial color, case metal, and strap choice. Any reference numbered IW371663 belongs to that same series, which means it carries the same basic architecture: a round polished case, a two-register chronograph dial, and a date window.
Why the number itself gets searched
- A buyer is offered a used watch and wants to confirm what the reference should look like.
- A listing appears at a price far under the pre-owned market and the shopper wants to know why.
- A counterfeit seller copies a real reference into a title so the listing matches what people type.
- An owner wants to know which details the common copies get wrong.
Movement: the hardest part to copy
Current references in this block run on an in-house IWC chronograph movement, while earlier generations used a heavily reworked Valjoux 7750 base. Both are expensive to reproduce, so copies hide a generic Asian chronograph behind a decorated plate. Open the caseback and look at the finishing underneath the rotor, not just on it. Genuine engraving is crisp and deep, the rotor text is clean, and the chronograph pushers start, stop, and reset with a firm, even click. A copy feels spongy, the chronograph seconds hand hesitates before snapping to zero, and the case often runs thicker than the real dimensions.
Dial, hands, and subdials
The Portugieser Chronograph places the chronograph minutes at 12, small seconds at 6, and the date at 3. Copies tend to shift those proportions or enlarge the date window. Check the printing under a loupe: genuine text is sharp with no fuzzy edges, applied numerals sit flat and level, and the leaf-shaped hands have a mirror polish with clean facets. On replicas, the subdial rings sit too shallow, the date font looks slightly wrong, and the sapphire crystal shows a strong blue tint from an angle instead of the faint coating on the real thing.
Case, crown, and caseback
Case work separates good replicas from obvious ones. Run a finger along the lugs and bezel for sharp edges that polishing should have removed. Look at the caseback engraving for the reference, the serial, and the material mark, and compare the digits against the paperwork. A genuine case serial and reference should match the warranty card and any service record.
Price is a signal, not proof
A genuine Portugieser Chronograph sells for several thousand US dollars at retail, and pre-owned examples hold a large share of that value. Replicas sell for a small fraction of the figure. A price far below the pre-owned range is a warning sign, but a high price proves nothing on its own, since counterfeit sellers price high to look credible.
Checks to run before you buy
- Ask the seller to confirm the reference and serial in writing, then match those digits to the caseback and card.
- Request macro photos of the dial, caseback, crown, and buckle in daylight.
- Have a watchmaker time the movement on a machine and confirm the beat rate and power reserve.
- Verify the warranty card, booklet, and box are consistent with the reference.
- Pay through a channel with buyer protection, or use an escrow service for a private sale.
The short version
A fake IW371663 is a replica IWC Portugieser Chronograph using a genuine reference number to look legitimate. The movement, the subdial layout, the case finishing, and the matching serial paperwork are the four points where copies fall apart, and any one of them is enough reason to walk away.