Mallory Ignition ACCEL timing computer 49340 - Manual (Page 11)

T HE MAP (M ANIFOLD A BSOLUTE / A IR P RESSURE ) S ENSOR C ONNECTOR
he MAP Sensor’s signal to the Timing Computer is through the flat, 3-pin connector.
nstall a 2- BAR MAP Sensor, according to its own instructions and plug the Timing
Computer’s male connector into the sensor’s 3-pin female port.
he MAP Sensor reads intake manifold pressure. This makes it possible for the Timing
Computer to adjust to a predetermined timing curve under Vacuum or Boost conditions.
Use an A CCEL / DFI 2-BAR MAP Sensor, Part# 74776
(No need for a 3-Bar MAP Sensor, even with high boost.)
he MAP Sensor measures pressure. Manifold Absolute Pressure is near 0 BAR at high
acuum, near 1 BAR at wide open throttle, and up to 2 BAR at about 14 PSI of Boost.
Vacuum sensing provides a linear advance of the Base Timing Curve from 0° to full
dvance during high vacuum conditions. I . E . You have set Maximum vacuum advance
t 10°. At wide open throttle there is little intake manifold vacuum and ignition timing
ollows the RPM curve. At light load (.5 BAR , about 15 inches of Hg ) the Timing Computer
dds 5° (half the 10° Maximum Timing) to the Base Timing Curve.
Boost retard works the same but in the opposite direction: Suppose you program a Boost
Retard value of 6° at the maximum sensing boost of 1 BAR (about 14 PSI ). At 0.5 BAR
about 7 PSI ) boost the Timing Computer retards ignition 3° from the Base Timing Curve.
T HE S QUARE , 4- PIN , M ALE I NPUT C ONNECTOR
he A CCEL TIMING C OMPUTER inputs from all kinds of trigger types, except distributor-less,
nd its digital, micro-processor controlled, rev-limiter will be as sensitive as your trigger.
We recommend an A CCEL Billetech Distributor or A CCEL Crank Trigger. Triggering inputs
re read through the square male connector: W HITE wire, or the P URPLE and O RANGE wires.
Your A CCEL + ignition system should already have this connector in place.
he W HITE wire’s input is in the form of
Square Wave. It gets this input from:
• All points ignitions
• Most fuel injections
• Some
HEI modules
he P URPLE and O RANGE wires get their
nputs from magnetic pickup or crank-
iggered systems
he P URPLE wire is a positive (+) input
nd the O RANGE is a negative (–) input.
(See chart for various connections.)
your system uses the W HITE wire you
ust isolate and insulate the P URPLE
nd O RANGE wires. If your system uses
he P URPLE and O RANGE wires you must
olate and insulate the W HITE wire.
* Older A CCEL Crank triggers may connect W HITE to P URPLE and B LACK to O RANGE .