Short answer

A fake IW371670 is a replica of IWC's 41 mm Portugieser Chronograph in stainless steel. The better replicas get the case proportions, dial printing and strap close enough to fool someone across a table. Almost none get the movement right, because IWC's in-house calibre 69355 has never been properly cloned. That one fact drives most of the tells worth knowing.

What the genuine reference actually is

IW371670 sits inside the 41 mm Portugieser Chronograph family that IWC moved to the in-house calibre 69355 in 2020. Earlier Portugieser Chronographs ran on a modified Valjoux base, so the older and newer versions look similar but behave very differently on the wrist.

  • Case: stainless steel, roughly 41 mm wide and about 13 mm thick
  • Movement: calibre 69355, automatic, column wheel chronograph, 46 hour power reserve
  • Dial: bicompax layout, elapsed chronograph minutes at 12, small running seconds at 6, no date window
  • Crystal: sapphire front, sapphire display back
  • Strap: alligator leather on most variants, with an IWC folding or pin clasp

I always check the subdial layout first. A real 41 mm Portugieser Chronograph puts the chronograph minutes up top and the running seconds at the bottom. If you see a date window at 3, or subdials at 3 and 9, you are not looking at this reference at all.

Where replica IW371670s land on the quality ladder

Roughly $60 to $120

Quartz inside, mineral glass, chromed alloy case. The small seconds hand at 6 ticks once per second instead of sweeping, which is the fastest way to kill the illusion. Case thickness is usually wrong by a full millimetre or more.

Roughly $150 to $300

Stainless steel with a Valjoux-style automatic and a transfer module bolted on to move the running seconds to 6. It works, but the pushers feel spongy, the case gets fat, and the rotor is loud. Decent at arm's length, obvious in the hand.

Roughly $350 to $550

The best of the replica market. Correct case dimensions, sharp dial printing, sapphire front and back, applied numerals with real bevels. The movement is still a decorated Asian automatic with an IWC-engraved rotor, not a 69355, and no factory has changed that.

The movement is always the giveaway

Turn the watch over and use a loupe. On a genuine 69355 you see Geneva stripes, a column wheel above the chronograph works, blued screws and clean engraving of the calibre number. On a replica you see a rotor with IWC text stamped or printed onto it, no visible column wheel, and jewel positions that do not match. Start and stop the chronograph while watching the pusher feel. A column wheel is short, light and crisp. A module on top of a 7750 clone is long, heavy and slightly sticky on reset.

Dial and case details I look at first

  • Leaf hands: genuine ones are faceted, polished on top and matte on the flank. Replicas are usually flat.
  • Subdial rings: real ones carry concentric snailed graining, many fakes print a flat texture.
  • Applied numerals: edges should be crisp with a clean bevel. The 12 is where sloppy replicas fall apart.
  • Printing: IWC and SCHAFFHAUSEN should have even stroke weight and consistent spacing. Swiss Made at 6 should sit dead centre.
  • Lugs and brushing: brushing runs one direction, lug bevels are sharp, and the inner edges feel finished, not raw.
  • Strap: alligator with the correct inner lining colour and stitch spacing. This is one of the most commonly swapped parts on fakes.

Price, papers and the reality check

A new genuine IW371670 runs in the region of eight thousand dollars at retail, and used examples hold value well. Nobody is selling a real one for six hundred dollars, new, in a box. If the deal only makes sense because the seller says it fell off a truck or came from a friend at a dealer, it is a replica and you should price it as one. Papers, a matching serial on the caseback and the warranty card, and the correct box are worth checking, but they are also the easiest things to fake.

Before you buy anything

  1. Confirm the subdial layout matches the real reference.
  2. Ask for a macro shot of the caseback with the movement visible.
  3. Ask for case thickness measurements, not just the diameter.
  4. Check whether the seconds hand at 6 sweeps or ticks.
  5. Compare the asking price against replica pricing tiers, not against retail.

Do that and you will know within two minutes whether you are looking at a cheap quartz knock-off, a mid-tier automatic, or the best replica the market currently builds. None of them is a 69355, and that is the line worth remembering.