Twin-Spark

THE TWIN SPARK IGNITION

Are two plugs better than one? In many cases they definitely are and double
ignition is becoming increasingly common in large modern engines. Yet the
origins of double ignition go way back into the annals of motoring history.
Here are the benefits and disadvantages, plus a brief history of double
ignition, a system that has become a burning issue on today's motoring
scene.

Systems using two spark plugs per cylinder, commonly referred to as double
ignition systems, were used in aeroplane engines. Apart from the very early
years of aviation history, aeroplane engines have always had two plugs per
cylinder for the obvious reason of improved reliability, and because with
aeroplane engines more than any other type of engine, reliability means
safety. If a car or motorcycle engine stops because of an ignition fault,
the vehicle simply grinds to a halt. Ignition failure in aircraft engines is
far more dangerous. To maximise reliability of the ignition system, aircraft
engines use not only two plugs but also two separate ignition systems with
two separate magnetos, so that the engine can continue to run on one system
if the other fails.
As the years passed, cylinder bores increased and engine capacity grew, and
double ignition began to prove useful in improving combustion efficiency
too. When this added benefit became apparent, it was only natural for double
ignition technology to be adopted by the car industry, and later by the
motorcycle industry also. In the early days of double ignition, the two
plugs were used mainly to overcome the problems of the irregular combustion
chamber shapes created by very round heads and raised piston crowns.
Double ignition was soon adopted almost universally in the motor racing
world. Its application on road vehicles was slow because it was considered
less beneficial. Over the year, however, air flow through combustion
chambers improved and four valve heads appeared, greatly reducing the need
for and the benefits of two plugs per cylinder. Many manufacturers therefore
lost interest in double ignition systems. In the world of car manufacturing,
Alfa Romeo stands almost alone for its renewed belief in the advantages of
double ignition. Alfa's Twin Spark engines are the new pioneers of double
ignition in today's automobile industry. In the motorcycle industry, Honda
was the first Japanese manufacturer to re-introduce double ignition in
recent times, installing it on its triple valve V twins. This is not the
first time for double ignition to be used in the motorcycle industry, of
course. Maserati single cylinder machines all had double ignition in the mid
1950's. Other singles to use double ignition were the twin cam Mondials and
the superlative Moto Morini 250, the latter with a valve angle of 90° -
100°. The Ducati 125 G.P. single with desmodromic valve gear also fitted
double ignition in 1958. Ducati abandoned double ignition only when it went
over to a more rational, smoother combustion chamber design. The last Ducati
engines to use double ignition were the 750 twins of the early 1970's, but
Ducati quickly returned to single ignition with these engines when it was
seen that double ignition gave no real advantages in terms of performance.
In the 1980's the first 4 valve production engine to feature double ignition
was the power unit of the Suzuki DR 600. Today Aprilia can be counted among
the many believers in double ignition, and the system that Aprilia uses on
its 1000 cc V twins is one of the technical features that make these engines
the most powerful and versatile in their class, so much so that they can be
used on many different types of motorcycle with only minor modifications. It
is generally recognised that double ignition makes power delivery smoother.
Double ignition engines snatch less as the revs rise. This benefit is most
obvious at medium revs, where increases in torque of around 15% can be
achieved. In the specific case of Aprilia's engine, maximum benefit is
achieved around 4,000 rpm. Under sports riding conditions (like circuit
riding) when engine speeds tend to stay within the 6,000 to 9,000 rpm band,
the improvement given by double ignition is less apparent. On Moto Guzzi
engines on the other hand, famous for their low revs muscle, double ignition
gives a very clear advantage, and most leading Guzzi tuners modify the
engines to fit it.
While double ignition gives real benefits in the field of racing, it is in
touring that the benefits really stand out. The main disadvantages of double
ignition are obviously higher production and maintenance costs.

Hope you all enjoyed that ?

CDIHL

 

The guy doesn't even credit the site he plagiarised. What an idiot!

http://www.aprilia.com/portale/eng/caferac_articolo.phtml?id=19

 

No **** off

 

I doubt he even knows the meaning of the word.
--
Deevo

Geraldton
WA, The Nanny State (® Corks)
www.wn.com.au/mckenzie

 

Interesting history, but next time.

use PARAGRAPHS so we can read wtf it is

Mike.S

 

Interestingly enough, my 1983 Honda VT500E has two spark plugs (and 3
valves) per cylinder. Honda are still using derivatives of that
motor[1] in the Transalp, Deauville, VT750, VT1100, VTX1300 and
VTX1800.

Unfortunately I hear that they stopped using offset crank pins[2] on
the cruisers so as to give them more "character".


BTH
[1] Pretty much any of the Honda range using a 52 degree watercooled
twin.
[2] That was done to eliminate most of the primary vibration.

 

I was going to interject "modern, sophisticated, specialismo
motorcycles such as production eighties Hondas", but decided
that would be Feeding The Troll.

Bah humbug. Hydro tappets rock, though.

-----sharks

 

Yeah, shoulda Snipped it.

 

Good Post , Thanks .

 

Damn right.


Hydraulic TapPat

 

Tappets which work on the "Cam will be here, he said he'd be here!"
principle ...

-----sharks (can't hear the fuckers over the rattly camchains
anyway)