Elliot Design Electronic Tachometers
These instruments have been developed to meet the demanding conditions
found in all forms of motorsport. The ultra reliable electronics have
been specifically designed to be compatible with most original equipment,
aftermarket, and contact breaker ignition systems.
All types are only for use with 12 volt negative earth systems, and
require a clean reliable 12 volt supply, a sound earth and a trigger
source from the vehicles ignition system.
How to select the correct tachometer for your application.
When you have chosen the type and style of tachometer that best
suits your application you first need to decide on the optimum scale.
To do
this you will have to determine your engines peak rpm and increase
this by 20% as this will give your optimum scale. For example, if
your engine’s
peak rpm is 7.500 then 7.500 x 120 = 9000, your optimum scale would be
0 – 9000 rpm. You need to select the standard scale that is
closest to your optimum.
The next step is to decide the calibration you need. For engines
using a conventional coil and distributor ignition this will be defined
as
the number of cylinders, for example a 4 cylinder engine will require
a tachometer calibrated for 4 cylinders. Where an engine is fitted
with crankshaft triggered ignition ( often called a lost or wasted
spark ignition
system ) two or more ignition coils will be used. When using the
negative terminal of one of these coils the tachometer will need
to be calibrated
for two cylinders (1 spark per crankshaft revolution), this is regardless
of the engine’s number of cylinders. Engine management systems
will almost without exception have a dedicated tachometer output.
You will have to refer to the manufacturers technical manual to determine
the ratio of pulses per crankshaft revolution your system delivers,
i.e.
1:1 ( 2 cylinder ) or 2:1 ( 4 cylinder ). Most quality aftermarket
systems have the facility to adjust the ratio.
Ordering information:
Once you have acquired all the relevant information, you will be able
to construct the part No for your tachometer as follows: Type: LC 80L,
Scale: 10, Cylinder: 4 , Dial colour: B, ( black ) or W ( white ) i.e.
LC 80 L 10 4 B.
Connection instructions:
Red wire: connect to 12 volt + supply.
Black wire: connect to zero volts chassis / frame or battery negative
terminal.
Green wire: connect to negative terminal on one coil or the tacho output
pin on the E.C.U.
