Mallory Ignition Mallory READ INSTRUCTIONS COMPLETELY BEFORE BEGINNING 29014 - Manual

YH AND YT ADVANCE CURVE CHANGE KIT
READ INSTRUCTIONS COMPLETELY BEFORE BEGINNING INSTALLATION
Part No. 29014
GENERAL INFORMATION
This kit allows the modification of the advance curve of any
Mallory distributor with the YH or YT advance system. Mallory
uses three different mechanical advance systems. Compare
the advance system in your distributor with the assemby
shown in Figure 4 to determine if you have a YH or YT
advance system. The advance can be seen by removing the
distributor cap (except for vacuum advance (V.A.) distributors;
the mechanical advance system in V.A. distributors can be
seen by removing the sight plug or plate on the side of the
distributor bowl).
Most Mallory V8 distributors are equipped from the factory
with one purple spring and one brown spring. The resulting
advance curve can be seen in Figure 1. This curve is a good
choice for most performance applications. The optimum
advance curve for any particular application depends on
many variables. Usually, a mixture of past experience and trial
and error are required to determine the best advance curve.
Two Stage Advance Curves:
Figure 1 shows the different two stage advance curves. All
two stage curves are obtained by using one purple spring and
one other color spring. (DO NOT USE TWO PURPLE
SPRINGS: This will cause erratic timing at low RPM). These
curves are called two stage because the slope of the curve
changes at about 1500 RPM. This is because the purple
spring is loose when installed and doesn’t become a factor
until after about 1500 RPM. Two stage curves are usually pre-
ferred for street driven vehicles (especially V8s) because the
quicker advance at low RPM provides good throttle response,
while the slower advance at mid RPM helps prevent detona-
tion. Full advance is in no later than 3500 RPM for good top
end power.
FORM 1367 04/05
Single Stage Advance Curves:
Any combination of springs which does not include a purple
spring will produce a single stage curve. These curves are nearly
straight lines. Figure 2 shows the curves obtained by using two
springs of the same color while Figure 3 shows curves obtained
by pairing springs of different colors.
Single stage curves are popular in 4 and 6 cylinder engines
(Many Mallory distributors for 4 and 6 cylinders are supplied from
the factory with two orange springs, see Figure 2) and for racing
V8s. Mallory V8 distributors whose part numbers end with “05”
are supplied from the factory with two pink springs.
In general, single stage curves provide less advance below about
1500 RPM (which is usually unimportant in a high RPM race
engine) yet allow full advance as low as 2000 RPM. In a race
engine, full advance is usually desirable at the lowest RPM that
the engine will see full throttle. However, in a street driven vehicle
using pump gas, single stage curves may induce detonation.
Spring Perches:
Each advance spring is connected to a post at one end and a
perch at the other end (see Figure 4). The curves in Figures 1,
2, and 3 were obtained by changing the springs only.
However, in some instance it may be desirable to bend the
spring perches SLIGHTLY in order to change the RPM at
which the advance starts. The advance in the distributor must
start at an RPM which is at least 100 RPM higher than the
idle RPM of the engine. Bending the spring perches to
increase spring tension will cause the advance to start at a
higher RPM.
For example, if the double grey spring curve of Figure 2
seems desirable but the engine idles at 700 RPM, the spring
perches can be bent (to increase tension) so that the advance
starts at 800 RPM rather than the 600 RPM shown on the
graph.
In a similar fashion, reducing the tension on the springs will
cause the advance to begin at a lower RPM.
INSTALLATION INSTRUCTIONS
1 MALLORY IGNITION www.malloryracing.com
List of parts:
Each curve kit includes 9 springs:
2 Pink
2 Orange
2 Grey 1 Purple
2 Brown
1 Set of YH Degree Keys