A fake IW371670 is a counterfeit copy of the IWC Portugieser Chronograph, a 41mm steel two register chronograph. The reference sits inside the IW3716 family. Depending on the production year it carries either IWC's in house calibre 69355 or the older 79350, which IWC built on a Valjoux 7750 base. That detail decides what you can actually check, so start there.
If you have thirty seconds, tilt the watch in angled light and study the two subdials. Genuine Portugieser Chronograph registers sit recessed, with polished chapter rings and fine circular graining inside. Copies print them flat. That flaw survives even on the more expensive fakes, and it is the tell I trust most.
What the real reference is
The IW3716 line is IWC's core Portugieser Chronograph. Stainless steel case around 41mm across and roughly 13mm thick, sapphire on both sides with anti reflective coating on the front and back, a date at 3, leaf shaped hands, applied numerals, and a slim railway minute track. Water resistance is rated at 3 bar, which is splash protection and nothing more. Movement is automatic, 28,800 vph, with a column wheel on current production and a power reserve in the mid forty hour range.
One warning before you compare anything: a lot of listings tagged IW371670 are simply the wrong reference pasted onto a different Portugieser. Confirm the number against IWC's own catalogue before you judge a watch as fake or real.
Movement tells
This is where copies fall apart, and where you need a watchmaker or a clear macro photo.
- Genuine finishing is even and deliberate: Geneva stripes on the rotor and bridges, clean anglage, polished screw heads. Fakes usually show heavy, shiny plating over rough surfaces.
- Asian 7750 clones run at the same beat rate but feel different in the hand. Wind one and you get a gritty, sandy sensation and a rotor that rocks loosely.
- Column wheel chronographs start and stop with a light, crisp click. Cam actuated copies need more thumb pressure and feel mushy on reset.
- Engraving font matters. The IWC lettering, the reference, and the serial number are cut deeply and consistently. Copies are shallow, uneven, or laser etched.
Dial, case, and hardware
- Sapphire with double sided anti reflective coating shows a faint blue or purple cast at steep angles. Fakes often have single sided coating or none.
- Lume on the numerals and hands should be bright and even. Copies are dim, patchy, or missing it entirely.
- The crown sits centered, engraving sharp, and screws down without grit. Fakes wobble or catch.
- Pushers on the real watch are polished and seat flush. Copies sit proud, with visible gaps.
- Straps are alligator on most genuine references. Fakes ship with embossed split leather or rubber, and the stitching runs crooked.
Price is the bluntest test
A current steel Portugieser Chronograph retails in the low five figures and trades used in the five to eight thousand dollar range depending on age and condition. Older IW3716 references settle lower, but not dramatically lower. Counterfeits sell for a few hundred dollars. If someone offers a new in box full set at a fraction of market, the paperwork is printed at home and the watch is a copy. Boxes, warranty cards, and hang tags prove nothing, because those are copied as easily as the dial.
What you give up with a copy
IWC will not service a counterfeit, and independent watchmakers struggle because the case parts, gaskets, crown, and pushers are not interchangeable with genuine components. The 7750 clone inside is cheap to replace but rarely regulated well, so timekeeping drifts. Resale value is zero, and selling one in the United States is trademark counterfeiting under 18 U.S.C. 2320, with civil liability on top. Customs can seize an imported copy, and you have no recourse when it happens. There is also the unglamorous part: unknown nickel content against your skin and gaskets that will not hold a splash.
How to buy safely
- Buy from an authorized dealer, a known gray market seller, or a private owner with service history.
- Request a movement photo and a straight on dial shot before money moves.
- Have a watchmaker open the caseback. Ten minutes of labor settles what hours of photo comparison cannot.
- Verify the serial and reference with IWC directly, or with an authorized service center.
- Pay in a way that leaves a paper trail, and walk away from anyone who pushes a wire transfer or a friends and family payment.
None of this is exotic detective work. It comes down to the subdials, the movement finish, and the price. Copies of the IW371670 have gotten better at the case and worse at the details, and the details are still where they lose.