I've always found that the V-Belts (alternator belt) that you get handed when you walk into a part store isn't quite right most times. So since I needed to find a shorter version for one of my high-amp alternator installs I figured now was a great time to finally do the research and find out what the RIGHT belt is.

Here's the final specs, which I'll update if more info comes to light:

Belt Angle: 36°
Belt Length: 965mm
Top Width: 9.5mm

My Selection based on the numbers is the ContiTech Brand. Actual installation experience to follow...

And here's my methodology:
First I grabbed an alternator pulley off the shelf and measured the V groove directly. This isn't particularly easy because the groove is so small, but I measured 34° (note there is a margin of error here).

Belt length is farily easy based on a couple sources. The 914 PET didn't list a belt for the 4 cyl (that I could find) but I happened to have a car with a very original looking belt. VW logo and everything. It lists the length as 965mm. Also looking up the VW part number on that belt comes back with a 965mm belt length. I used a belt length calculator and entered measurements from a stock fan/alternator setup and also arrived at 960mm.

Top Width is listed on my presumed-OE belt as 9.5mm. I had a 11mm top width belt here and it stands up out of the groove too much.

What's Available
Here's the belts I looked up for a 73 914 2.0, in a spreadsheet. I would love to add more listings to this file if you have any.

Ahah! I wondered why I felt a ridge across the belt and the pulley itself. Good info, Mark!

PET list a different part number 068 903 137D which is 10 x 965
Illustration 902-05 position 3 for the 914, but the same part number for a 912E is 960 x 9. Illustration 902-10, catalog 911 1974- 1977 no position

Hi Mark,

I finally pulled the alternator and replaced the pulley. I need a new belt and am happy to help with this project. PM me and I'll send you my address...

Your'e the man Mark!

Same belt used on the BNW E 30's ?

9.5mm is common on many german cars ,many use the 10mm but it isn't right,it won't fit down low enough and wears its way in until it becomes loose,@ the same time it polishs the pulleys so the belt will slip or chirp after being re-adjusted....seen it SO many times.
Most people overtighten belts cause they can't be bothered finding the correct tension,Marks comment about pulley angle was 36degrees...not sure but remember 35 off the top of my head...anyway.
IMO any belt running over pulley o.d. is just not doing the whole job.

I have a stock 75 2.0 daily drive I can test on...PM if I can help

-Robert