1. What's the difference between a trigger from a magneto and a crank trigger?
2. What's the correct air gap on the crank trigger pick (Sensor)?
3. Why should a capacitor PN 8830 be installed with a retard control?
4. What's the minimum voltage requirement for the Pro Mag Timing Control?
5. What's the maximum amount of timing I can retard with the Pro Mag Timing Retard?
6. How often should spark plug wires be replaced?
7. How often should coils be replaced?
8. Can the Rev Limiter damage the engine?
9. Why can't I start my engine?
10. How can I trouble shoot my mag at the racetrack?
11. Why does my tachometer jumps around on the rev-limiter?
1. What's the difference between a trigger from a magneto and a crank trigger?
The main difference is the stability of timing in most cases the generators are driven by a drive system from the block in a single or dual configuration. To provide clearance the drives are designed with an offset driven by a belt arrangement or a set of gears. Belt stretch or backlash can affect timing accuracies as well as the cam to crank drive suffering from the same problem. This theory was unproven until RacePak developed their newest software that can monitor timing during a run.
Here we have a run showing the difference in timing in the generators vs. crank triggers. Notice how much the timing changes with the generator and how much smoother the timing is on the crank triggers. With the timing moving that much from base timing it explains the some of the catastrophic failures.
back to top2. What's the correct air gap on the crank trigger pick (Sensor)?
This is a common question that is affected by other outside sources like:
Crank Trigger Wheel Diameter:
(smaller vs. larger, larger being better because of higher magnet velocity)
Starter Type:
Block mounted vs. External (Blower Mounted)
Battery voltage:
12 Volts -24 volts (block mounted) 36 - 48 Volts (External starters)
Induction:
Blown vs. Non-Blown (Blower more engine drag especially when re-stripped)All of the above will play a roll as to what the proper air gap will be for that engine combination. Typical air gap should be between .040 to .080 the low side is deemed by crank flex and high side is hard starting to no start. If the engine fires up repeatedly, that can ensure the air gap is correct, and crank flex has been accounted for.
Air gap should not have a performance effect of the magneto system, however it has been noted that an excessive air gap can create a timing offset in the Race Pac data recorder by as much as 2º depending on the air gap.
Another solution to the problem can be a "Change Over Switch" that will allow starting with the generator and once started it can be switch to the crank trigger pickups. This can be done using a 4 pole, Double-Throw switch for a dual mag installation or a 2 Pole, Double-Throw switch for a single mag installation (See wiring diagrams*). A word of caution here, extending magnetic pickup leads can introduce EMI (Electro magnetic Interference) or RF (Radio Interference) into the system, this can cause random misfire and erratic timing, use at your desecretion. Make sure to use a quality switch; most switches will cost $50 to $80 dollars DO NOT USE A CHEAP SWITCH! Also keep in mind that high vibration environments can cause switches to switch on and off during a run possibly resulting in engine damage.
3. Why should a capacitor PN 8830 be installed with a retard control?
The purpose for the capacitor is to buffer the action of the "ON / OFF" switch to the battery in a monetary open condition due to severe tire shake or vibration. With the capacitor in place the retard box would never see the open condition, if it did, the entire ignition system would lose power (Shut completely off) and re-ignite again, possibly resulting in engine damage. Click on diagram below.
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4. What's the minimum voltage requirement for the Pro Mag Timing Control?
The minimum voltage will be 5.0 Volts to as high as 18.0 volts. Keep in mind that other devices connected to the battery (other than the Pro Mag Timing Retard and Six Shooter) like the air switches that can draw more current than the Pro Mag Timing Retard and Six Shooter. One good test would be to monitor the voltage with a meter and trigger the switches or timers via the WOT switch and watch the voltage.
5. What's the maximum amount of timing I can retard with the Pro Mag Timing Retard?
The largest retard chip we make specify for the Pro Mag Timing Retard is 30º these can be purchased at the MSD trailer or special ordered from the Pro Mag Department. They only cost $8 each.
The Pro Mag Timing Control was initially designed with a maximum of 15º of retard, but at the racers request we have pushed the unit to 30º of retard. By doing this the calibrations have changed slightly from 15º to 30º here are the values:
16º = 16º, 17º = 17º, 18º = 20º, 19º = 21º, 20º = 22º, 23º = 23º, 24º = 24º, 25º = 25º, 26º = 26º, 27º = 27º, 28º = 28º, 29º = 29º, 30º = 30º
Note that a 21º and 22º modules are missing this is because the calibration is NOT Linear at this point. The unit was not intended to work past 30º and it was also our intent to replace the unit with the Pro Mag Programmable Controller that would be very accurate from 0º to 35º. But the Programmable unit is not approved for use by the NHRA. (Caution: These degree modules are calibrated specifically for the Pro Mag Timing Retard and will NOT work with other MSD products.)
6. How often should spark plug wires be replaced?
Spark plug wires are a consumable item like oil in the engine, they should be changed on a frequent schedule that is determined by how often they run. A routine schedule of cleaning, inspecting and checking the resistance of the wires should be done as a routine maintenance program of the car. Some teams even keep a logbook of the resistance of when the wires were built to compare after running.
Some of the most common problems can come for the actual wire crimps that can be resolved by re-crimping the terminals or replacing the terminal. The terminals are designed as a conductor crimp so the conductor does not have to be bent over which can fracture or damage the conductor making it read a higher resistance than normal.
The resistance should be 40 to 50 ohms per foot once the measurement is noted that value should not change. The only other facture that can not be checked is the outside jacket, other than cleaning and a visual inspection looking for abrasion, cuts and pinholes, the jacket will deteriorate in time due to the amount of energy being transferred through the wires.
The coil wire should be replaced often as it gets hit 8 times more than the other wires. Big budget teams replace wire set about every third race while most others would replace them every 6th to7th race. There really is no gauge as to how often to replace wire set. Remember the wires are the actual delivery system of the spark energy to the spark plug that will affect a performance of the engine if not up to par.
7. How often should coils be replaced?
This is a tough question to answer, there are only two reasons to replace coils when one is "Open" or has a shorted winding. In either case most can be found with a simple L.C.R. (Inductor, Capacitance and Resistance) meter. Notice that there are several numbers inscribed on the back of all coils.
One set is the date code (which had been changed to an easier method to read) and the second and third sets are the inductance values of the coils. In this case the numerical value does not represent any form of performance like 709 vs. 899 these numbers are simply inductance values of the windings. These numbers are used to monitor a change within the coil. Keep in mind that these numbers are relative to the meters being used, several variables can account for the values: coil temperature, lead length, and meter model and meter frequency output. So if you purchase an LCR meter these numbers will differ slightly from actual numbers on your coils. Once you acquire a meter it would be wise to log these values and periodically check them to see if they have changed. Theoretically, once a coil is built and has run successfully down the track it should never fail unless due to exterior damages.
In the beginning (1994) our coils were capable of extremely high voltages. The coils were capable of 55,000 volts to 60,000 volts as time passed we found that these voltage capabilities were unnecessary and were resulting in a high yield of coil failures prior to shipping. We redesigned the coils limiting the output voltages to 45,000 volts, this resulted in cooler running coils that were not capable of destroying themselves yielding higher percentages of higher quality coils.
Prior to purchasing a set of coils they have already met several of our quality benchmarks. One of the outstanding test is the coil must run for 5 minutes running at 1800 RPM without a coil wire attached, this test is performed 3 times before arriving the packaging department. This is to test the quality of the potting material, assuring that porosities or air bubbles are not present. In most cases if either are present the coil will fail prematurely. Eventually coil usage will degrade coil life or performance, unfortunately translating this into a number of passes, races or years is difficult to determine.
8. Can the Rev Limiter damage the engine?
NO! If and when the engine reaches the selected rev limit point the Rev Limiter will only drops cylinders randomly. The Rev Limiter is only as accurate as the input signal. The Rev Limiter is based on the incoming input signal from the magnetic pickup at the base of the generator or the pickup from the crank trigger. When the generator pickup is used it's not uncommon for the limiter accuracy to widen due to the mechanical slop or movement at high engine speed. This has been evident by a RacePak data recorder showing the timing variance (see above: What's the difference between a trigger from a magneto and a crank trigger?) In order to maximize the Rev Limiter accuracy it's advised to install a crank trigger.
The Rev Limiter Chip is a precision resistor with 0.1% accuracy that calibrates the Rev Limiter circuitry. The RPM value should not change by heat or vibration nor can a resistor be "Shorted". A resistor can be "Open" which would then result in a "No Rev Limit"
What happens when the engine hits the Rev Limiter?
The Rev Limiter will randomly drop cylinders at the specific RPM and in most cases seen by a data recorder the limiter can lock-into a specific cylinder sequence. Meaning that it will drop or choose certain cylinders at that specific RPM. The EGT in those cylinders can remain cooler than other cylinders.
MSD Rev limiters have been around since the early 1980s in all forms of racing and since then we have not resulted in a damaged engine. If anything the MSD Rev Limiters have saved engines from damage due to countless broken drivelines and axles.
9. Why can't I start my engine?
In most cases it due to "Cranking RPM" or lack of RPM, the Pro Mags must see a minimum of 200 to 250 RPM to start. There are several variables that can contribute to a "NO Start" situation:
Starter type
Battery voltage
Newly re-striped blower*
Blower OverdriveIf Crank Triggered excessive Crank pickup air gap (See "What's the correct air gap on the crank trigger pick (Sensor)?"
Insure that the starter is of a Hi-Torque type and that the batteries are fully charged. Checking battery voltage while cranking will insure batteries are fully charged. In some cases 16 to 18volts can aid to a faster cranking speed. A word of caution: Not all starters can tolerate higher voltages and most block-mounted starters should not exceed 18Volts.
*A newly re-striped blower can have enough friction to lower the cranking speed, try spraying silicon spray to lubricate the rotors. If that doesn't do it remove the blower belt (For testing purposes) and check for spark, this should free the motor up enough that if you do get spark your cranking speed is too low to start the engine with the blower. If you do not get spark remove the spark plugs and crank the engine again (With the plugs removed the engine will spin quickly) if still no spark check the following:Inspect all connectors to insure the pins have not back out and insure that the "grounds" are correct (see diagram) or call us. (915) 857-5200 and ask for the Mag Tech. We can then walk you through several other steps.
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10. How can I trouble shoot my mag at the racetrack?
There is several ways to trouble shoot the system in a "NO SPARK" situation:
1. Is the rotor turning, something in the drive could have broken.
2. Is the starter turning fast enough?
3. Are the starter batteries fully charged?
4. Has the blower been re-striped? Try silicone spray in the blower.
5. Is the Kill switch stuck "closed"? Sometimes the contacts can arch or weld themselves closed. (Disconnect for test)
6. Check the 4 pin connectors and pins to see if any of the pins have backed out of the connectors.
7. If Crank triggered, check the crank pickup air gap it should be .030 to .080.
8. Check the pickup resistance with an ohm meter it should read:3/8 pickup = 115 Ohms
3/4 pickup = 68 Ohms
Internal pickup in the generator = 600 Ohms
11. Why does my tachometer jumps around on the rev-limiter?
It sounds like the tachometer is connected to the 8132 Tach converter that is connected to the coil. When the Rev Limiter is active it randomly drops cylinder by not lighting certain cylinders. The coil then does not spark on those cylinders so the Tach converter does not generate a tach signal for the tachometer causing it to jump around. Click on diagram below for more details.
You will need Acrobat Reader
to view diagram, download it here.
One way to eliminate the tachometer jumping is the use of our Pro Mag Timing Retard PN 8168 that has a tach output. This unit will insure smooth tach trigger during Rev limiting because it not connected or depending on a coil signal. Click on diagram for more detail.
You will need Acrobat Reader
to view diagram, download it here.
12. When should I replace my cap and rotor?
Again these parts are a consumable item of the ignition system and the power level that we're running at these parts will wear and at a higher rate than accustom to than non MSD magneto products. Typical wear will have a burnt or worn edge that's not as crisp or sharp but should not hurt performance. The life of a cap and rotor on a 44-amp system will shorter vs a 12 or 20 amp system.
13. How many Six Shooters can I use?
A Six Shooter is just a selector module that can switch different modules by +12 Volts from a timer or pressure switch arrangement. Six Shooters can be piggy backed together with as many units as desired 2 pack 3 pack 4 packs etc. This would allow for a much finer or smoother transitions between timing changes.
