Choosing the Right Distributor for your VW
Aircooled VW owners have an assortment of options when choosing a distributor for their engine. If you only look on the surface it seems simple: The “obvious” choice is the Bosch 009, right? Not necessarily. Once you do a little research, you’ll find a variety of stock units (including the SVDA unit), as well as the Bosch 009, 010, and 050 series, and finally the Mallory, MSD, and the age old Magneto. So which one is “best”?
Each of these units is excellent – for the right application. In this article, I will clarify the right time and application for each option available. You can read the entire straight through, or skip directly to your area of interest using the quick links below:
Before we rush ahead, we are going to use some terminology, we may as well define it for you so you know what we mean!
Centrifugal Only Distributor. This distributor changes ignition timing based on RPM ONLY, without any vacuum sensing.
SVSA = Single Vacuum, Single Advance Distributor. This is a Vacuum ONLY distributor, there is no centrifugal advance mechanism.
SVDA = Single Vacuum, Dual Advance Distributor. This distributor has centrifugal and vacuum advance operating independently.
DVDA = Dual Vacuum, Dual Advance Distributor. The same as the SVDA, but also has a Vacuum RETARD port. One vacuum port is for advance, the other is for an idle retard, which improved emissions a lot!
“Old Faithful”, the VW Stock Distributor (Vacuum Advance)
We will start at the obvious place, which is the beginning. Up through the late 60s, VW supplied their engines with the stock distributor, which was a non-smog distributor (emissions were not an issue). These vacuum advance only distributors do their job well, and all are dependent on a vacuum signal from the carburetor, (with the exception of some early type 2s, which were chronically under-powered and used a centrifugal only distributor). Stock units work VERY well when installed in stock or near-stock engines with 28 or 30-1 and 30-2 series carburetors. Most complaints are related to a defect of some sort (bad points, condenser, worn out distributor), or a problem that is giving symptoms of a bad distributor, but is actually fuel system related.
One of these two modifications are the most common:
The carburetor is changed to something other than stock, and it is almost always missing a vacuum port for the vacuum advance distributor to operate properly. No port = no vacuum.
or the high performance engine does NOT have a proper vacuum signal due to a long duration camshaft.
Cam overlap can cause a drop in vacuum, and obviously, the vacuum advance on a stock carb and distributor won’t work together properly.
The Bosch 010 and 019 Distributors
Bosch came to the rescue with the 010 Distributor for early hot-rodders. This Cast Iron Bodied Distributor eliminated the vacuum advance system, and used engine RPMs ONLY to dictate the ignition timing. For high performance engines of the time, this was the perfect solution, since these engines were usually run at idle or full throttle! This was because the aftermarket carburetion being used back then did not have the vacuum port needed for the vacuum advance distributors.
The 009 Distributor
In 1971 (in the USA) the VW engines were shipped with a “smog” distributor, which had a vacuum retard in addition to the vacuum advance. This is also the year when most VW engines were also updated to the dual port head and intake manifold configuration, along with a change in carburetors from the 30 PICT series to the 34 PICT series, which has the additional port for the vacuum retard. These new carburetors were also LEANER in their operation, since they had to conform to the new tailpipe standards that were being ramped up in the early 1970s.
The 009 distributor was introduced, and was a very inexpensive “replacement” unit for VW engines, and it was almost a duplicate of the earlier 010 distributor.
These 009 distributors were (and still are) sold by the ton. Early VW engines (pre-71′) had no problem, but the smog engines when equipped with the 009/010 distributors had a pronounced and annoying “flat spot”. A “flat spot” is a hesitation just off idle, and can range from being almost unnoticeable to getting broad-sided or rear-ended by approaching cars! (Many 009/34 equipped owners mistake this hesitation for POWER. They don’t notice the hesitation, but they DO notice the kick in the back of the seat once the engine catches and it starts accelerating! They mistake this for “more power” since there is such a difference between the stumble and actually operating properly.)
The Vacuum Advance Distributors do not have this hesitation since they advance the timing when the throttle is opened as part of their operation. Obviously, the 009/010 is only rpm based, and this vacuum advance doesn’t happen. When a 009/010 is combined with the lean SMOG operation of the 34 series carb, the flat spot is the result. The most common “solutions” are all modifications to the carburetor, which richens up the fuel delivery in various forms, whether it’s the idle circuit, the main jet, and/or the accelerator pump circuit.
The error with these “fixes” is that they are curing a symptom, not THE PROBLEM. The problem is the lack of additional advance just off idle, not lean operation. The stock distributor/34 carbs didn’t have a hesitation!
Enter the SVDA distributor. A production VW distributor, made by Bosch, which is modified to provide the 009 advance curve (close enough), and a vacuum advance unit too! Believe it or not, there is an additional advantage to the vacuum advance (on engines that have the proper vacuum port; 34 PICT series carbs), and that is the gain of 4 mpg improvement over the 009/010 distributor! Same performance, plus 4 mpg improved mileage, and NO FLAT SPOT.
30 PICT Series carburetors can NOT use the SVDA Distributor since the vacuum signal is not correct and won’t pull the advance in on the small canned SVDA (you notice the early distributors use larger vacuum cans than later distributors because the vacuum signal is different).
When the carburetor is changed to one which is missing the proper vacuum port, obviously the vacuum signal is lost, so the centrifugal advance units ARE the proper distributor for this application. Now you are lost in a multitude of choices: North American 009, Kühltek 009, Bosch 010, Bosch 050, Centrifugal Only Mallory, MSD, Pertronix Billet Distributor, and Magneto. Which one to use?
What you want is to set your ignition timing about 4 degrees retarded from the point where detonation begins. This setting means the flame front will meet the piston at the top, maximizing cylinder pressure and the time (crank degrees) to push the piston down, making the most power. If you ignite the charge too late, the pressure doesn’t build until the crank has rotated some, and you lose precious crank degrees (HORSEPOWER) of work. If the charge is ignited too early, the flame front will hit the piston ON THE WAY UP, and this is a sure-fire way to destroy your engine very quickly.
What is needed is to find the timing point at EVERY RPM point where you are around 4 degrees retarded from detonation under full throttle, since this is the “ideal” time for our spark to occur. Obviously, you would leave yourself a safety zone of 3-4 degrees of timing at all points to CYA in case of bad gasoline, clogged main jet, vacuum leak, abnormally hot engine, etc. The power difference between detonation and 3-4 degrees of retarded timing from this point is negligible, so riding the ragged edge of timing is not worth the risk!. Detonation does NOT have to be audible for it to turn your expensive mechanical marvel into junk in short order.
Finding the Advance Curve
Ideally, you would remove all advance from the distributor, and run a locked timing. You then put the engine on a dyno, and play with timing across the RPM band from idle to red line at full throttle (finding the timing where you are 4 degrees from detonation) and then chart it. Then, you remove the locked timing from the distributor, set your initial timing to match what you found was best at idle. Next, match the distributor’s curve to match what you found to be best on the dyno by changing weights and springs in the distributor.
If you have the patience and time to set up this custom curve, and have a heavily modified engine, your patience will be rewarded! Get yourself a Mallory/MSD distributor. You will find they are VERY adjustable. The easiest method to follow is very straightforward. Find the MAX advance point your engine tolerates (between 30-40 degrees BTDC) above 3000 RPM. Now find the place where it responds best at idle. It may be 15-24 degrees BTDC. You may find that this much advance causes starting difficulties when the engine is hot, so be sure to check this out! Ignition before top dead center causes “negative torque” and that’s what suddenly STOPS your engine from cranking. Avoid this, or use a retard that is activated during cranking.
Now, you know the two critical points in your advance curve. You only need to figure out how FAST you want the advance to come in. I recommend being conservative, and kick the advance in SLOWLY and see how the engine responds. Keep adjusting it (it requires distributor disassembly) so it comes in quicker and quicker, until you detect detonation (problem). Back it to the previous setting, and you are DONE with the centrifugal advance. Now, dial in 10 degrees of vacuum advance, and adjust the advance so the carb(s) will actually activate it and you are done! PHEW!
Frankly, though, finding the advance curve using this method isn’t practical for most of us.
The 009/010 is best used for stock rod ratio engines, where you do not want to do all this customer ignition curve work. Let me first say that I’m not a fan of the 050. The 050 has a different advance curve, and it’s more suited for short rod engines (like the type 4), or engines with a bigger crank and shorter rod (78 stroke with Porsche length rods, etc). The Bosch 050 has not been made for a long time, finding tune up parts for it can be quite difficult, the Centrifugal Only Mallory Unilite is the best “replacement” for the Bosch 050 Distributor.
If you are using an out of the box distributor (009/010/050), you have to set the timing as advanced as you can so it doesn’t detonate at full throttle (where you would have a problem with a centrifugal only distributor). Problem with this is, you are setting the WHOLE CURVE BASED ON THE MAX TIMING AT ONE PLACE. This in itself is significant. You are finding the point in the rpm range where you can’t advance any more, even though at many (all) other rpm points you are too retarded! THIS is exactly why setting up a custom distributor advance curve is the ideal solution, but not everyone has the time/patience to set it up. Obviously a fully adjustable setup like a programmable Haltech makes this very easy on a dyno since you just tap a few keys and you are on your way, not like changing springs and weights in the distributor every time you have to make a change. But if you like it the old fashioned way, you can simply buy the Centrifugal Only Mallory Unilite, or the Mallory Unilite With Vacuum Advance if you have the proper vacuum ports on your carburetors!
Now I want to cover one MORE ignition topic that is important to consider. The ignition is separated by PRIMARY and SECONDARY parts. The primary ignition is the low voltage side; points, condenser, etc. The secondary ignition is the high voltage side; Ignition Coils, Distributor Caps, Ignition Rotors, Spark Plug Wires (Ignition Wires, or Ignition Leads), and Spark Plugs. The primary side of the ignition is responsible for the triggering of the spark, and the secondary side is responsible FOR the spark itself.
In my opinion, Ignition Points are obsolete (sorry to be blunt). Unless you like messing around with them, replace them with some sort of magnetic triggering device (Compufire, Pertronix, Compu-Tronix, etc; Aircooled.Net prefers the Pertronix at the present time). These do NOT increase your spark quality (like some claim) compared to a properly operating points triggered ignition. However, they do not deteriorate like conventional points/condenser ignitions. They are exceptionally reliable, and they will be rock steady at all RPMs, which can not be said for points. Basically, the magnetic pickup assures optimum triggering all the time. Simply buy the magnetic pickup points replacement unit and throw the Ignition Points and Condenser in the glove box in case you have a problem with the magnetic unit. The Pertronix Flamethrower Billet Distributors come with the magnetic pickup as part of the distributor, so you don’t have to worry about it on that model.
This is another place where large improvements in engine operation can be gained. Frankly, the stock Bosch Blue Coil is only adequate to about 2500 RPMs, and the spark quality deteriorates from this point and up. The problem is with the coil’s primary voltage (12-14V). As engine RPMs increase, there is less time for the primary voltage at the coil to create the required magnetic field that generates the high voltage spark we need at the Spark Plugs. There are two solutions: 1) increase coil current. The problem with this is that you will burn out points (if equipped) much faster, since the coil’s current is passing through the points. 2) increase the coil’s primary voltage. This is the solution that Jacob’s, Universal, MSD, and other companies have decided to use. There is no drawback to this solution other than cost. We carry the Mallory CDI Systems at Aircooled.Net.
Once the secondary ignition is improved with a CDI (Capacitive Discharge Ignition), the spark plug gap could be increased to 0.040-0.045″. Be aware that you may have to re-set your timing, since the larger plug gap and better spark can speed up the time the flame front reaches the piston (detonation). You will find smooth running at all temperatures and INSTANT starting (not like before), with a 10-15% increase in mileage. This savings in fuel will pay for the CDI quickly! When we use a CDI (Capacitive Discharge Ignition) we keep the Spark Plug gap the same as stock, which stresses the secondary ignition components a lot less, and you still see the benefits of running a CDI (Capacitive Discharge Ignition). For Spark Plugs, in Aircooled VW Engines we have a very strong preference for the High Quality NGK Spark Plugs.
If you don’t want the complexity of a CDI (Capacitive Discharge Ignition) you can simply put a High Output Ignition Coil on the engine, just make sure to use a version with a 3 Ohm Impedance, so you don’t burn up your Ignition Points or Points Replacement Device!
High Output Engines
Another issue that you must be aware of is that high output ignitions MAY have a problem with the small diameter Distributor Caps on the Bosch units. There is a reason the MSD, Pertronix Billet Distributors, and Mallory Distributors have a large cap, and that is to minimize the possibility of the spark jumping to a contact that it is not intended for! Another problem is that the Bosch Rotor has a resistor in it, which WILL burn out in a short period of time if used with a high output ignition. You can dig it out, and solder a solid piece of brass in its place (it’s between the tip and the cap contact area). The Mallory Distributors has a solid rotor so they are immune from this problem!
A last option for ignition system is the Magneto. A Magneto is basically a Generator, Ignition Coil, and Distributor in one unit. Watch out, they’re heavy! These are wonderful products, but they have a VERY limited application. In my opinion, a Magneto should ONLY be used in applications that DO NOT HAVE A BATTERY, or that are REQUIRED to have self supporting ignition systems (aviation?). Computer ignition systems have better sparks than Magneto’s, and Magnetos are very heavy and they draw power off the engine to generate their spark. If you have a battery and a computer ignition, the computer automatically steps up the battery voltage to whatever the engine needs even if battery voltage drops to a low level. Having a Magneto AND a battery/generator/alternator is redundant, in my opinion. But if the vehicle has no battery and is externally started, the Magneto is the obvious choice!
Distributor Application Summary (the article in a nutshell, without all the details).
Stock Distributor – For stock engines.
050 – For engines with a relatively short connecting rod. We personally don’t like the Bosch 050 distributor, instead use the Mallory Unilite w/o Vacuum.
Centrifugal Only Mallory Unilite, or Mallory Unilite With Vacuum Advance – For modified engines where the owner/builder wants to customize the ignition curve The fully adjustable vacuum advance increases your gas mileage by 4-5 mpg on the highway, and increases part throttle power. The fact that it works with the Stock Bosch Blue Coil OR any aftermarket CDI (Mallory, Jacob’s, MSD, etc.) is icing on the cake. These features make Mallory Unilite With Vacuum Advance the premier distributor in the VW Industry!
Pertronix Billet Distributor – For modified engines with a custom ignition curve, magnetic pickup, and that can be easily connected to a MSD ignition unit (5, 6AL, 7AL2/3, etc).
Haltech/Electromotive – For the high tech junkie that wants infinite adjustability in their ignition timing.
Magneto – For engines with no battery or source of electricity (generator/alternator).
So – that’s it! Let us know if this article has been a help, and of course when you decide to order, please consider Aircooled.Net!
Article Written April 3, 1999
Article Updated April 12, 2012