|
KNOCK CONTROL
If your engine's knocking hard,
you better get a Safeguard
Written By: Larry Henderson
Let's face it. For the forced
induction crowd, modifying cars can be tough. Talk to almost any 5.0
Mustang owner running a blower and you can hear colorful stories about
blowing head gaskets. Does this mean blowers are bad? Absolutely not,
but as you go beyond entry-level kits they require a certain amount
of restraint and tuning knowledge to avoid engine damage. Those running
high compression, turbos or large amounts of nitrous encounter the same
problem. Why? Sometimes we get too aggressive with our tuning. Other
times the engine combination is simply incompatible with the type of
fuel we want to run, but in many cases problems arise from factors we
have no direct control over. Things such as a hot day, low humidity,
or just a bad tank of gas all increase an engine's tendency to detonate.
As a result, to keep the engine making maximum safe power, we have to
fiddle with boost retards while listening carefully for detonation.
To make things worse, all this has to be done while driving down the
road. If only there was a better way. Now there is. Enter the J&S
Electronics Safeguard.
The Safeguard from J&S
Electronics is a compact unit that does some pretty amazing things.
First and foremost, it is a superb knock-sensing timing retard. It is
also a velvet touch rev limiter. Finally, it slightly increases the
stock ignition's output. Before going into great detail about the unit,
it is helpful to have a good understanding of the different types of
detonation and a clear description of the terminology being used. First
of all, detonation refers simply to the very rapid, uncontrolled explosion
of the air-fuel mixture when it reaches the point of auto-ignition.
The auto-ignition point is the temperature and pressure at which an
air-fuel mixture will ignite without a spark. This point is determined
primarily by the fuel being used. Higher octane fuel has a higher auto-ignition
point than lower octane fuel. Knocking, or pinging is the sound we hear
when the air-fuel mixture detonates. It goes without saying that if
this rapid uncontrolled explosion occurs while the piston is still on
its way up, cylinder pressure will skyrocket. This exceedingly high
cylinder pressure is what blows head gaskets, holes pistons, cracks
blocks and generally makes you have a really bad day.
Detonation can be caused by several different things. It can occur in
a high-compression engine when the heat and pressure from compressing
the air-fuel charge exceed the fuel's auto- ignition point even before
the spark plug fires (pre-ignition). In this case timing is not the
problem, fuel octane and compression must be addressed to overcome this
problem. Detonation can also occur if there are "hot spots"
in the combustion chamber caused by carbon build-up, too hot spark plugs,
etc. In this scenario, the intake charge can be pre- ignited, or ignited
in another area of the combustion chamber leading to two flame kernels,
abnormally fast burning, and you guessed it, detonation. Fortunately
for us, the most common cause of detonation in street Mustang's comes
simply from too much timing advance. In this case the flame is ignited
by the spark plug. Normally as the flame kernel expands, cylinder pressure
climbs, but before it reaches the critical point, the piston is already
on its way down, thus averting disaster. In the case where timing is
too far advanced, pressure starts building too early and because the
piston is still coming up, pressure builds quickly, reaching auto-ignition.
Detonation occurs and cylinder pressure again goes through the roof.
Now that we have a working knowledge of detonation and what causes it,
let's take a detailed look at the Safeguard. Like many OEM applications,
the Safeguard utilizes a knock sensor. This device is essentially a
high quality microphone that screws into the engine's block. The knock
sensor is tuned to respond most strongly to those frequencies that are
known to accompany detonation. The sensor sends its acoustic information
to the Safeguard's control unit where this data is processed by the
Safeguard's Digital Signal Processor (DSP). The DSP employs a proprietary
knock sensing scheme that is impressively capable of discriminating
between knocking (even knocking that is not audible to the driver) and
normal engine noises (valvetrain, accessories, etc.).
As soon as detonation is detected, the Safeguard responds by retarding
timing in 2, 4, or 6 degree increments depending upon the intensity
of the detonation. It accomplishes this very quickly, before the troubled
cylinder can fire again. As soon as detonation stops, the unit slowly
advances the timing (2 degree increments) until detonation returns.
The unit then pulls timing back out. This closed-loop control continues
keeping the engine making maximum power, but preventing engine damage.
It is important to note that the Safeguard is capable of retarding all
cylinders or each cylinder individually. This way each cylinder is given
all the advance it can safely use. The seat-of-the- pants difference
between the two settings is quite surprising, indicating that by retarding
only the detonating cylinders, the Safeguard is increasing the engine's
power. According to J&S, this can amount to ten to twelve percent
more torque depending upon your application.
The sensitivity of the unit is set by a knob on the unit. This setting
will be different for different combinations, but is not dependent upon
operating conditions. Once you set the sensitivity properly, you don't
have to worry about it until you modify the engine again. The ideal
sensitivity setting is sensitive enough to prevent the engine from knocking,
but not so sensitive that the unit retards under normal driving conditions.
In addition to the sensitivity setting, the unit has a built in connector
that can be hooked to the TPS, MAF, MAP etc. This will prevent the unit
from retarding on deceleration. This is a thoughtful feature that improves
driveability.
As mentioned earlier, the
Safeguard is also a rev-limiter. Setting the rev limit is quite simple
with a volt meter. You merely monitor the voltage between a test point
and ground while adjusting a knob on the unit. The RPM limit will be
proportional to the voltage indicated on the meter (Ex. 6 volts = 6000
RPM). When this RPM is reached the unit will cut spark to every third
cylinder. This results in a very smooth one-third drop in power. It
is important to recognize that by dropping every third cylinder, fuel
will not build up in any particular cylinder because the non-firing
cylinders will be different on each engine rotation. This prevents excess
fuel from washing the oil film off the cylinder walls, which could result
in excessive cylinder bore and ring wear.
An excellent option available with the unit is the Dual Monitor. This
attractive little device incorporates an air-fuel monitor that utilizes
the stock left oxygen sensor. This saves you the expense and hassle
of installing a new sensor and mounting bung. The unit does not interfere
with the EEC's closed-loop operation. The air-fuel meter does nothing
to alter fuel delivery, but it is an invaluable tuning tool, and it's
also fun to watch. The Dual Monitor also incorporates a knock retard
display. This shows the amount of retard required to eliminate detonation.
When the Safeguard is set to retard all cylinders equally, you will
see a single red light that indicates retard amount. When retarding
cylinders individually, the display will light up one red light for
each cylinder indicating the retard amount for each cylinder. This feature
is useful in setting the sensitivity of the unit.
Installation is surprisingly
simple and well within the grasp of the average Stang banger. This is
due in part to J&S's excellent Ford-specific instructions. In this
case the unit was installed on a daily driven, supercharged '91 Mustang
GT Convertible that was plagued with a recurrent detonation problem.
The unit went in without a hitch in just over four hours. A quick twist
of a screwdriver and the rev limit was set at 6200 RPM. At first, the
unit was set to retard all cylinder's equally. A few quick blasts up
and down the road were all it took to dial in the sensitivity.
The effect of the unit is both noticeable and impressive. Instead of
knocking under full load, the display simply lit up between two and
four degrees of retard. Once we were confident that everything was working
properly, the unit was set to retard all cylinders individually. Immediately,
acceleration was noticeably improved, and knocking was still under full
control. Finally, the initial timing was bumped up using Anderson Ford
Motorsport's PMS (similar to Crane Interceptor II). Again, part throttle
acceleration was notably improved and knocking was nowhere to be heard.
The Dual Monitor now read six to ten degrees of retard.
As impressive as the Safeguard is and as confidence inspiring as it
can be, it must be remembered that insufficient fuel octane, excessive
boost, and too much compression can still destroy an engine no matter
how much timing is backed out. On the other hand, when an engine is
properly set up, ignition retard can be an exceedingly effective method
for controlling detonation. It is in this facility as a timing retard
that the J&S Safeguard has no equal.
In conclusion, the J&S Safeguard does what it claims and it does
it well. The test car has run flawlessly with the unit under many months
of hard street use. The best part of it is detonation is out of mind
and out of sight. You just punch the gas and enjoy life. That's what
its all about.
|
