Choosing the Right Distibutor


This article, authored by John Connolly of Aircooled.Net, originally appeared in "VW Trends" and is reproduced here (adapted) with permission. The original article can be found on the Aircooled.Net Web site.

A concise Summary is given at the end of the article.

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 distributors (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:


Stock Engines

"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, and emissions were not an issue. These vacuum advance distributors do their job well, and all are dependent on a PROPER 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 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 the following two modifications is 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.
  • The high performance engine does NOT have a proper vacuum signal due to a long duration camshaft.

Cam overlap can cause a drop in low RPM vacuum, and obviously, the vacuum advance on a stock carburetor and distributor won't work together properly. We have introduced the most advanced distributor the VW market has ever seen to solve this problem, which we have coined the name "SVDA." SVDA stands for Single-Vacuum Dual-Advance (centrifugal and vacuum advance). While the "SVDA" term describes about 20 different "stock" units, OUR SVDA was developed here, for modern fuels and the needs of the modern driver in an older vehicle. "SVDA" is used to describe ANY distributor with a combination centrifugal and vacuum advance, but this is NOT the same as the Aircooled.Net SVDA, so just understand the difference.


The 010/019 Distributors

Bosch came to the rescue with the 010 and 019 Distributors for early hot-rodders. This distributor eliminated the vacuum advance system, and used ONLY engine rpms 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! :-)


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. The engines were also changed to the dual port configuration, along with a change in carburetors from the 30 PICT series to the 34 PICT series, which had the additional port for the vacuum retard. These new carburetors were also LEAN in their operation, since they had to conform to the new tailpipe standards.

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 and 019 distributors.

These 009 distributors were (and still are) sold by the ton. Early VW engines (pre-71') had no problem because the 30 PICT and earlier carburetors are jetted with an Air/Fuel ration of 11.5:1! The 34 PICT engines are closer to 13:1, and these "smog" engines when equipped with the 009/010 distributors have 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 immediately upon throttle opening. 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 carburetor, the flat spot is the result. Current "solutions" are all modifications to the carburetor, which richen 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 carburetors didn't have a hesitation!


The Single-Vacuum Dual-Advance (SVDA) Distributor

Enter the SVDA distributor. Developed by Aircooled.Net, this distributor is essentially a centrifugal-advance distributor (009 advance curve), with a vacuum advance assist to help prevent hesitation in all of those stop-n-go situations in city traffic. The mechanical advance takes over out on the highway; the vacuum/mechanical advance design of this distributor provides an excellent advance curve under the entire range of engine speeds/loads.

This is THE distributor to use on your stock engine with Solex 30PICT-3, H30/31 PICT series, and 34PICT series carbureted 1600 Beetle through 1974 (75-79 with carburetor) and Type 2 1600 through 1971. It is NOT recommended for use with the 30PICT-1 or 30PICT-2 carburetors because the vacuum signal is incorrect for the vacuum assist to work properly. If you have been running an original dual-vacuum distributor on your 71-74 Beetle or 71 Type 2 and you switch to an SVDA, you will need to cap off (plug) the retard vacuum port located on the rear (rear is rear) of the carburetor.

An additional advantage to the SVDA distributor is a gain of 4 mpg improvement over the 009/010 distributor! Same performance, plus 4 mpg improved mileage, and NO FLAT SPOT. The additional advance of the vacuum advance also returns cooler running on the highway; most users report an oil temperature decrease of about 10-15 degrees over 60mph.


Modified Engines

When the carburetor is changed to a carburetor with no vacuum port, you have to either add the port to the carburetor, which is a delicate operation, OR use a centrifugal advance distributor for this application. Now you are lost in a multitude of choices: 009, 010, 050, Mallory, MSD, 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 gas, 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 redline 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 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 carburetor(s) will actually activate it and you are done! PHEW! To limit the advance, you simply bend the stop tabs, or you can slip a piece of vacuum hose over the post, to accomplish the same thing.

Frankly, though, finding the advance curve using this method isn't practical for most of us. If you get a Mallory, we can tell you which spring combination you need, and what initial and full advance setting to use, to set it up perfect your first try! We sell and use a lot of these, and our experience with the VW engines in various combinations, along with feedback from our technically savvy customers, has allowed us to dial on the combos perfectly if you tell us the engine size, cam, compression, vehicle it's in, along with your intended use.

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 914 and Porsche engine bus guys (72' and newer) are the ones usually using the 050.

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/Autronic/Electromotive 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.


Ignition Basics

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; coil, cap, rotor, wires, and plugs. The primary side of the ignition is responsible for the triggering of the spark, and the secondary side is responsible FOR the spark.


Primary Ignition

In my opinion, points are obsolete (sorry to be blunt) for all applications where you are on the ground. Find one modern car that still uses them! :-) If you are in a PLANE, use points, since they always "work" well enough to get you back on the ground, even if they are burnt. In an automotive application, unless you like messing around with them, replace them with some sort of magnetic triggering device (Compufire, Pertronix, etc; Aircooled.Net carries both). Contrary to popular belief, these devices 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, so your engine always has that "tune up" feel to it. 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 points and condenser in the glove box in case you have a problem with the magnetic unit. Mallory Unilite's comes with the optical pickup as part of the distributor, so you don't have to worry about it on that model. MSD distributors are a magnetic pickup, but they MUST have a CDI in order to translate the low voltage magnetic signal to a spark the engine can use. If the CDI craps out, you are walking if you have an MSD. The Mallory can work with or without a CDI. If the CDI craps out, you simply wire straight to the coil, then drive home, and then get the CDI fixed. :-)


Secondary Ignition

This is another place where large improvements in engine operation can be gained. Frankly, the stock Bosch 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 (12-14 volts). 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 plugs.

There are two solutions:

  • 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.
  • 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 or Jacobs, the spark plug gap can 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!


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 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) or we sell the rotor already modified. The Mallory distributors has a large cap and stout rotor that solves both problems also.


The Magneto

A last option for ignition system is the Magneto. A Magneto is basically a generator, 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. Race cars with no battery run magneto's, it saves weight and complexity (some of these cars don't even have starters for the same reason).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. If the vehicle has no battery, and is externally started, the Magneto is the obvious choice. Some fans of the "Old School" look of vintage performance run magnetos on their cars because that was popular in their retro period.


Distributor Application Summary

(The article in a nutshell, without all the details).

  • Stock Distributor - For stock engines.
  • SVDA Distributor - For 34 PICT, 30/31 PICT, Progressives, and Dual Carburetors with Ported Vacuum Ports. Stock or stockish appearance.
  • 009/010 - For modified engines, where no ignition fine tuning is desired.
  • 050 - For engines with a relatively short connecting rod. (I personally don't like these distributors).
  • Mallory Points or Unilite - 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 coil OR any aftermarket CDI (Jacob's, Mallory, MSD, Universal, etc.) and stock plug wires is icing on the cake. These features make this unit the premier distributor in the VW Industry!
  • MSD - 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). These MUST have a CDI, and MSD compatible plug wires.
  • 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) or a Retro look to their engine.

So - that's it! Let me know if this article has been a help you -- and, of course, when you decide to order, please consider Aircooled.Net as a source for your Parts needs!

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