Here's a place that all VW owners need to check. VW's are famous for lousy battery and alternator cables. I found bad ones on both of our project Corrados. If there is excessive resistance in a positive battery cable or alternator cable , you will likely experience slow cranking, cranking then starting, yellowish light from the headlights and battery problems (from insufficient charge). If you have a bad ground cable, these plus many other strange problems can arise. After repairing all of these cables, I noticed an immeadiate improvement in power. Whether this was because of the increase in fuel pump power, ignition power, or computer operation, I can't say, but the improvement was very real.
Here's how you can easilycheck your cables: get yourself a cheap digital voltmeter and measure the voltage directly at the battery and again at the alternator with the motor running and all the accessories (including lights and a/c) on. You will find that the alternator is putting out more voltage than ever gets back to the battery. This is because of minute resistance in the cables and the high current being drawn through them. In our case, I barely got 12 volts back at the battery.
Next you need to find out which cable is at fault. Do this by reading the voltage drop across each cable. Touch one lead of the voltmeter to the negative battery post and the other lead to the engine block. You will read a very small voltage, which is the drop across that particular cable. Short cables can have a drop of less than 0.1 volts DC. Anything more than 0.2 volts is marginal. I had a ground cable with over 0.5 volts drop. It looked perfect, but the multimeter didn't lie. Without the correct voltage I wasn't really playing with a full deck of cards....
Spark and timing I played around quite a bit with spark plugs and found nothingin the expensive factory plug to warrant it's use (except long life). I tried different plug wires too but found no performance gain here. It does seem to help, however, if you keep the inside of the distributor cap clean. High boost makes delivering a spark difficult, and sometimes films or deposits inside the distributor cap can rob voltage. Replace your rotor and cap regularly. Beware of aftermarket parts, which may not be exact replacements!
At the reccomendation of some Firehawk racers, I added a spacerto the knock sensor to isolate it (a little) frrom the block. This is the sme idea that VW used on the Pikes Peak record-winning G60 back in 1989, and on the VW Motorsports race engines.
Don't try to remove the knock sensor entirely or mount it on rubber, because the computer must have a proper noise signal from the knock sensor in order to work correctly. Otherwise the system goes into a failure mode; not the hot tip for performance. The 1 inch thick piece of aluminum was supposed to make the knock sensor less sensitive. It seemed to help a little. The plug between the knock sensor and it's wiring harness has been upgraded by VW to one with gold pins. Apparently, this connection is critical. Once again, Cramolyn (from your local electronics store) or an antioxidant product like it is useful for keeping this connection clean and oxidation free. I also tried advancing the timing, but it never helped on the G60, and the car refused to knock even with a huge amount of advance. This knock sensor seems to be real sensitive.