by Brian Verbeek
A properly adjusted 009 will most likely be set at around 7, 8, 9 deg BTDC. I would not recommend 20 deg static timing with 009 as the total advance would be something like 40 to 45 deg BTDC--I'm pretty sure that'll destroy any VW engine.
If you're swapping distributors and you want to determine the new static timing point, take your old static timing point (OST) get the distributor advance of the original distributor (ODA), and the new distributor advance (NDA), and make sure to covert distributor degrees to crankshaft degrees (1 distributor deg=2 crankshaft deg).
New Static Timing= (OST+ODA)-NDA
if (I just put in any numbers):
Old Static Timing, OST=7.5
Original Distributor Advance, ODA=20
New Distributor Advance, NDA=21
New Static Timing=(7.5+20)-21
New Static Timing=27.5-21
27.5-21= 6.5 crankshaft degrees (if you get a negative number it's ATDC).
After you adjust the timing you can experiment a little, as the formula is not a guarantee things will be fine. It only helps to set the new distributor so as to give the same amount of total advance as the stock distributor had. The new static timing point might not let the engine idle properly, or the new distributor might have a very aggressive advance curve, and might give full advance at a different RPM. Be careful with settings of more than 30 crankshaft degrees total advance static+distributor). Be sure to check your engine's temperature frequently until you're sure things are fine. Be extra careful when you have an extractor exhaust system, as that will make it harder to detect detonation.
How to make your own '009'
You can make your own 009 if you have some old distributors laying around. Either call your Bosch importer to ask the spec sheet of your distributor#, or stick the distributor in an engine with a (properly) degreed pulley and use a timing light to see how much it advances without the vacuum advance connected. The spec sheet is the better way to go as you can ask for a 231 178 009 spec sheet at the same time so you can compare the distributor you have to the 009.
Remove the vacuum canister and the point plate from the distributor body. The point plate is actually two plates. Remove the top one. Now you have the 009 point plate. It's exactly the same (actually, most of the time, early 70s C+V distributors), you only need to tap the hole for the screw that holds the points (M2 or M3). The holes are in the proper location, but note that the points have moved, so make sure that you change the #1 marking on the edge of the distributor body accordingly so that #3 will get its less-advanced-than-the-others spark. If you're lucky you have the distributor body with an oval hole for the vacuum canister. If that's the case you can use an oval plug from another distributor to plug it. These plugs are either black or white plastic or stamped out of sheetmetal. You might end up with a distributor that suits your needs better than an 009.
I would only recommend a centrifugal advance distributor for engines with (big) dual carbs or that have other modifications to their intake system that disturb the vacuum signal in the manifold and thus would not actuate the vacuum advance properly. The stock distributor should work properly on a stock engine.
All numbers mentioned above are from the top of my head. It can't hurt to double check them.