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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:
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 (emissions
were not an issue). These vacuum advance 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 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.
- 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. We have introduced the most advanced distributor the VW market has ever
seen to solve this problem.
The 010 Distributor
Bosch came to the rescue with the 010
Distributor 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 carbs 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 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. 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 carbs didn't have a hesitation!
The SVDA Distributor
Enter the SVDA distributor. A production
VW distributor with the 009 advance curve (close enough), and a vacuum
advance unit! 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.
The drive-ability of the SVDA/34 carb
has to be experienced!
30 Series carbs 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).
Modified
Engines
When the carburetor is changed to something
larger than stock, 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: 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, IMO. 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/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).
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. However, we have a new distributor that makes this task EASY; inquire
for details.
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). Unless you like messing around with them, replace them
with some sort of magnetic triggering device (Compufire, Pertronix,
etc; Aircooled.Net carries the Compufire). 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 points
in the glove box in case you have a problem with the magnetic unit.
The MSD distributor comes with the magnetic pickup as part of the distributor,
so you don't have to worry about it on that model.
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
(12-14V). 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 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 Universal and Jacob's 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). Our new distributor has a large cap
and bulletproofrotor, so that's easy!
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 (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. 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.
SVDA Distributor - For 34 PICT equipped
engines.
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).
Our New Unit- 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 withthestock coil OR any aftermarket CDI
(Jacob's, MSD, ours, etc.) 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).
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 me know if this
article has been a help you…and, of course, when you decide to order,
please consider Aircooled.Net!
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