In a message dated 7/6/2001 1:31:55 AM Pacific Daylight Time,
vinttr4@geneseo.net writes:
<< Haas anyone seen actual dyno results of an engine with and without an
MSD ignition? >>
Jack and all:
Here's my 2 cents. I used to design OEM electronic ignitions for
Ford/Motorola, and have tested numerous aftermarket units under controlled
conditions. Before I comment on MSDs, here as some general comments.
1. There are two basic types of electronic ignitions, Capacitive Discharge
(CDI), and Inductive Storage. Inductive is the most common and uses the
ignition coil for storing the energy to make the spark. CDI uses a capacitor
fired through a coil to make a spark. Inductive are generally capable of
delivering more total spark energy to the plug. A CDI can fire at a higher
voltage than Inductive (which can burn through a fouled plug, for example),
but has a MUCH shorter spark time, resulting in overall lower spark energy.
Points and condensor are Inductive storage type. Most electronic ignitions
are electronic variations of points & condensor that eliminate the wear-out
and failure mechanisms of points & condensor.
2. In today's lean-burning, low emissions engines, keeping the spark fully
lit in a swirling chamber is the challenge. This is also the same challenge
in high compression, high performance engines. The preferred solution is a
high ENERGY igntion, as ALL OEM igntions are designed. Inductive storage is
the choice for this as all OEM auto manufacturers employ.
3. Multiple spark igntions (like MSD and others) are a trade-off. Instead
of delivering one long, high energy spark, they deliver several to many short
sparks. Thus, if the spark blows out, there's another spark to relight the
mixture, insuring complete combustion. What this means, though, is that in
between sparks, there's NO spark, resulting in overall LOWER energy than a
continuous, high energy spark that would occur over the same period of time.
4. The spark energy is the product of the spark voltage times the spark
current, times the time. The voltage is essentially controllled by the spark
gap, and the current and time by the available energy source (the inductance
of the coil and turns ratio, and how fully charged it is). The time is
limited by the RPM between spark firings. Thus, in a 4 cylinder engine you
have twice as much time to fire as in an 8 cylinder engine at the same RPM.
5. From my experience, multiple spark discharge ignitions can offer
performance improvements on certain engines where the mixtures are hard to
keep lit, due to cylinder head designs, and/or flow/swirl patterns in the
cylinders. For most engines, though, a single high energy spark is more than
adequate. Problems typically arise at higher rpms where the time is
decreased and the overall energy from any system decreases due to the shorter
time available to deliver full energy to the spark plug.
6. MSD has done an excellent job of promoting their system through big time
racers. However, their expensive, heavy, and complex hardware often is
outperformed on specific applicaitons by much simpler systems. I have also
been disappointed by the reliability of their systems (ever see a pro racer
using MSDs with less than 2 systems mounted...1 as a backup)?
7. If the addition of an MSD ignition, or any other aftermarket ignition
provides a HP increase on a dyno on your engine, then you can be sure you
were not having complete combustion previously. Whatever solution provides
the best spark ignition solution for your engine application is the one to
use. In some cases an MSD might be an improvement, for others, not.
8. There are other factors that also come into play besides the type of
igntion, and that includes the ignition advance curve (mechanical, or
electronic), the type and heatrange of plugs, the type of wires used, the
type of ignition coil, and whether or not you have a distributor. All of
these factors can impact the amount of energy delivered to the spark plug for
ultimately lighting the mixture in the cylinder.
I hope this sheds some light on the subject for you.
Myles H. Kitchen
1965 Lotus Cortina Mk1 #128
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