Timing,ignition and compression
We Alway prefer and recommend the use of CB Performance magna spark ignitions. They work very well and the adjustabilltiy is unmatched. Type 4 build will be built with petronix dizzy as they fit and adjust well in the stock type 4 tin.
Before we get into timing I have a small note on compression. These are my thoughts and finding, stuff that has worked really good for me. On all air cooled Vw engines T1-4 I have found it is best running comp ratios between 8 and 9 to 1. My average target for type 1 style engines is 8.5 and 8.8 to 1. This makes the fuel burn more efficient. This means less heat and better fuel milage, along with easier starting ,idling, throttle response, tuning and fuel mixture. I also have read and believe the higher cylinder pressure helps press the exhaust charge out. With the new head and piston combos for the type 4 engines we normally land between 8 and 8.2 to 1. Modified T4 or Porsche style type 4 heads allow for higher comp ratios with less CC chambers, again shooting for 8.5 to 8.8 on street engines.We have countless engines on the road both long haul and rippers running sub 9 to 1 ratios on 87 oct pump gas. A lot of owners use these Vws to travel far and wide, good gas is not always available unfortunately .Yes, I know that sounds crazy but there is so much junk in todays gas that prevents knock. My Personal bus is 8.8 and has seen extreme heat,10-12 hour consecutive day runs ,94mm cylinders with no issues. Now that being said your engine must be jetted, timed, and dialed in. Our bigger and more street strip engines will run more compression for both Cam over lap and and power. If your engine is 9 to 1 plus it is best to run 91 or 93 octane fuel. Timing sometimes will be reduced to 32 max advance but can be run up to 34 depending on the engine.Higher comp is more likely to knock or ping. So higher octane fuel and reduced timing is used.
Most Vw engines I see benefit from from a higher initial timing. This helps take up some fuel, smoother idle, and better jet transfer. This may take a one size lager idle jet then what the market states. Type 1-3 dual carbs I set 10-14 initial single carbs 12-18 initial depending on the cam shaft. Type 4s initial around 12-14.
Now on to max timing, with lots of time, builds, miles, and tuning. I am a fan of timing I always push the timing max. Some where are 32-36 with comp ratios up to 9 to 1. With my builds I have continuously found a drop in head temp with more advanced timing. You definitely want to be careful with this if you do not know what you are doing, our engines are already set up and tuned for timing like this. Always double check your spark plugs, head, and oil temps to make sure your engine is performing correctly.
With the new age of super chargers, we have built a couple of these engines and kits. Even with these kits we had huge head cooling with advance initial timing, running 12 degree initial and 24 max. the first of these super charged engines we built constantly built insane, ever climbing head temps with the manufacturers setting. After days of running on the stand I decided to push the timing and re-jet. We not only stopped the head temps from constantly climbing but return them to a steady 200 degrees on the stand. Again I believe serious tuning should be left to a Professional.