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175A Upgraded Alternator Installation Manual

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This is the installation guide for our 175A six phase alternator.


Failure to follow this warning could result in personal injury, death or property damage.

Improper installation, adjustment, alteration, service, maintenance, or use can cause explosion, fire, electrical shock, or other conditions which may cause personal injury or property damage.

Consult a qualified auto electrician, service agency, or Classic Retrofit Ltd for assistance.

Read and follow all instructions and warnings.
Please consider your and other people's safety before testing.

About the Alternator

The 175A alternator is a joint development between Classic Retrofit and WOSPerfomance. It is the only unit available for the classic 911 that can offer continuous high current levels without failure due to heat.

The alternator contains modern Denso internals with the patented ‘hairpin’ windings. This is a 6 phase alternator which is more efficient therefore produces less heat. Units of this design are fitted to millions of modern production vehicles with high continuous load requirements.

Unlike ‘rewinds’ based on the standard Valeo/Bosch casing, these units have an internal fan that can draw air over the internal windings. The ‘hairpin’ windings also allows air to flow in between them, unlike the bundled wires in older units.

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We have tested the unit up to 150A continuous with the single pulley. The unit is capable of producing 175A but a polyrib belt is almost certainly necessary at these levels.

The idle performance is exceptional, typically producing 75A on a 1.8 ratio pulley. As a comparison, the 90A 911 alternator only produces 40A at idle.

Note that RPM quoted is for the alternator. Typical 911 pulley ratios are around 1.8. So for example engine idle at 950 RPM would be 1710 RPM at the alternator.


Producing 75A at idle, this alternator is ideal for your 911 if you want to fit:

  • Heated Screens and Seats
  • Driving or Rally Lamps
  • High Power Stereo Equipment
  • Electric A/C or Heating
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The alternator mounts inside the fan housing. As the cars evolved, Porsche increased the standard alternator length and the fan housing was machined accordingly. There are three different fan housing machining depths but unfortunately you cannot tell from the casting number alone.

The 175A unit is the same length as the early 1965 to 1973 alternators and is a direct fitment for these fan housings.

Mid year (1974 to 1983) cars with the 70A/75A alternator require the use of an 10mm adapter ring sold separately.

Late year cars (1984 – 1989) with 90A units require the use of two spacers (10mm and 11mm) to make up the 21mm offset.


Note When installing this alternator, the following wiring MUST be uprated:

Alternator GND(-) to engine case

Alternator Battery+ to Starter Solenoid+

We provide the cable set with the alternator.

  1. Remove the existing fan housing, fan and alternator from the car. If the existing alternator uses an external regulator follow the Porsche Technical Bullet (reproduced at the end of this manual) prior to installation.
  2. Replace the engine GND strap with the heavy duty black cable. Replace the main alternator cable with the heavy duty red cable. This needs to be routed to the starter solenoid. Easier to do this on a ramp. Some cars may need a hole drilling in the engine tin above the oil cooler but be VERY carefully. The engine tin in this area can often be removed with the engine in place.
  3. Compare the old alternator length with the new unit. Use the adapter(s) if necessary to make the unit match in length. Either no adapter (early), 10mm adapter (mid) or 21mm (late). Tap the adapter(s) on to the alternator with a rubber mallet until fully seated.
  4. Position the alternator in the fan housing as shown in the photo.
  5. Porsche use brown for earth so be sure to connect these to GND. Additional positive cables are red and the lamp cable is usually blue. When the alternator is in the car, the cables should be attached as shown:
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