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Why Upgrade from a Stock Ignition System?
A vehicle’s stock ignition system is designed to meet a broad range of operating conditions while keeping manufacturing costs low. It delivers a reliable spark under normal driving, but it quickly reaches its limits when you push for higher rpm, boost, or compression. Upgrading to an MSD 6AL programmable digital ignition system transforms your engine’s spark delivery, leading to measurable power gains, crisper throttle response, and improved drivability. This article provides a comprehensive look at the performance benefits, total costs, and practical installation tips so you can make an informed decision before swapping out your stock ignition.
Understanding the MSD 6AL Ignition System
The MSD 6AL is a capacitive discharge ignition (CDI) box that stores energy in a capacitor and releases it to the coil in a powerful, short-duration pulse. Unlike stock inductive ignitions that build coil energy slowly, the 6AL delivers a spark that is typically 110 millijoules—significantly more than the 30–50 millijoules of most factory systems. This extra energy ensures a robust flame kernel even under lean mixtures or high cylinder pressures.
Key Features of the MSD 6AL
- Multiple Spark Discharge (MSD): At lower rpm (below 3,000), the system fires a series of sparks over the plug’s firing duration, ensuring complete combustion. This reduces misfires and improves idle quality.
- Built-In Rev Limiter: The 6AL includes two programmable rev limiters—one for hard cutoff and one for a softer “soft touch” limit. This protects the engine from over-revving during missed shifts or drivetrain failures.
- Wide Input Voltage Tolerance: Operates reliably from 12–18 volts, making it compatible with high-output alternators and voltage drops during cranking.
- PNP and Aftermarket Distributor Compatibility: Works with most conventional points, magnetic pickup, and Hall effect distributors, as well as MSD’s own Pro-Billet or Ready-to-Run distributors.
Power Gains: What the Dyno Shows
Real-world dyno results consistently show that swapping a stock ignition for an MSD 6AL can unlock 5–15 horsepower on naturally aspirated engines and 15–30 horsepower on forced-induction or nitrous setups. The gains come from three main areas:
Improved Combustion Efficiency
A stronger spark ignites the air-fuel mixture faster and more completely. This reduces cycle-to-cycle variation, allowing the engine to burn leaner air-fuel ratios without stumbling. On many carbureted engines, tuners report they can lean out the mixture by 0.5–1.0 full ratio after the upgrade, which directly improves fuel economy and reduces exhaust gas temperature.
Cleaner High-rpm Operation
Stock ignition systems often struggle above 6,000 rpm because coil dwell time becomes insufficient to saturate the coil. The MSD 6AL’s capacitive discharge design is not dwell-limited; it can fire reliably up to 15,000 rpm. This allows the engine to rev freely without ignition breakup, which is critical for race applications.
Better Nitrous and Boost Tolerance
When using nitrous oxide or forced induction, cylinder pressures climb dramatically. A stock spark may be blown out by the pressure, causing a misfire that can detonate the cylinder. The MSD 6AL’s high-energy spark cuts through those pressures, maintaining ignition under extreme conditions.
Cost of the Upgrade: Detailed Breakdown
The total cost of switching from a stock ignition to an MSD 6AL depends on your current setup and whether you perform the work yourself. Below is a realistic breakdown for a typical V8 street machine or muscle car.
| Component | Price Range (USD) |
|---|---|
| MSD 6AL (PN 6420) box | $250 – $400 |
| MSD Blaster 2 or 3 coil (recommended) | $40 – $80 |
| MSD spark plug wires (8.5mm or 9mm) | $60 – $120 |
| Spark plugs (copper or iridium, gapped to 0.035–0.045”) | $20 – $50 |
| Distributor if upgrading (e.g., MSD Pro-Billet) | $150 – $300 |
| Installation labor (shop) | $150 – $400 |
| Miscellaneous connectors, wire, and loom | $20 – $40 |
| Total (DIY with existing distributor) | $370 – $650 |
| Total (shop install with new distributor and wires) | $600 – $1,200 |
Note: Many vehicles with electronic distributors (GM HEI, Ford TFI) can use the MSD 6AL with an adapter harness; however, HEI owners must bypass the module inside the distributor to prevent double-sparking. Budget an extra $30 for a bypass kit if needed.
Step-by-Step Installation Guide
Installing an MSD 6AL is a weekend project for most DIYers. Follow these steps carefully to avoid damaging the unit or your vehicle.
Preparation
- Disconnect the negative battery terminal and verify power is off.
- Locate a mounting position for the MSD box away from heat sources (exhaust manifolds, headers) and water spray. Inside the passenger cabin behind the kick panel or under the dash is ideal if your engine bay is tight.
- Gather tools: wire cutters, strippers, crimpers, a multimeter, and a soldering iron (preferred) or quality butt connectors.
- Review the wiring diagram included with the MSD 6AL. For most distributors with a magnetic pickup (two-wire), you will connect the small red wire (switched 12V), small black wire (ground), and the two white wires that go to the pickup leads.
Wiring the MSD 6AL
- Power connections: Connect the large red wire (10-gauge) to the battery positive via a 30-amp fuse or directly to the starter solenoid “BAT” terminal. Connect the large black wire to chassis ground (engine block or frame).
- Switched 12V: Connect the smaller red wire to a key-on ignition source (e.g., the original coil + terminal or a fuse panel circuit).
- Distributor pickup: Connect the two green/violet wires (from the MSD harness) to the distributor’s magnetic pickup leads. Polarity matters—green to one pickup lead, violet to the other. If the engine runs rough, swap them.
- Coil wiring: Connect the MSD 6AL’s orange wire to the coil positive (+), and the black wire to coil negative (-). Remove any external ballast resistor or dropping resistor—the MSD 6AL handles voltage regulation internally.
- Rev limiter modules: If you purchased optional plug-in chips, insert them into the module slot on the 6AL box. Default factory setting is 6,000 rpm.
Post-Installation Checks
- Reconnect the battery and turn the ignition to the “RUN” position (do not crank). Listen for the MSD box to emit a brief whine (it charges the capacitor).
- Use a timing light to check ignition timing. The MSD 6AL does not alter base timing; verify it matches your previous setting.
- Start the engine and let it reach operating temperature. Look for misfires, backfiring, or erratic idle—these may indicate incorrect wiring or a bad ground.
- Check the spark gap: With high-energy ignition, you can often increase the plug gap 0.005–0.010” over stock for better low-rpm torque. Start with manufacturer recommended gap and test.
Common Installation Mistakes and How to Avoid Them
Many first-time MSD 6AL installers run into issues that are easily preventable.
- Incorrect ground path: The MSD box draws high current. Grounding the large black wire to a painted surface or rusty bolt will cause voltage drop and erratic spark. Scrape to bare metal and use a star washer.
- Using the original coil with ballast resistor: If your stock ignition had a ballast resistor (common on Chrysler and Ford points), bypass or remove it entirely. The MSD 6AL expects a full 12V to the coil positive wire.
- Double triggering with HEI: If you keep the HEI module in the distributor while adding the MSD 6AL, the module will also fire the coil. Remove the four wires connecting the module to the coil or use an MSD HEI bypass adapter.
- Overlooking RFI suppression: The high-energy spark can create radio interference. Use resistor spark plugs (R-type) and quality spiral-core plug wires. MSD sells a noise filter for the 12V power wire.
- Assuming the rev limiter is a substitute for a tachometer: The MSD 6AL’s rev limiter is a safety device—it should not be set as a hard shift-point. Always use a tachometer for accurate rpm readings.
Tuning and Optimization After Installation
Once the MSD 6AL is running, fine-tuning can extract even more performance.
Spark Plug Gap Adjustment
With high-output CDI ignition, you can widen the plug gap to 0.040–0.050” on naturally aspirated engines, and 0.030–0.040” on boosted or nitrous engines. This increases the flame kernel size, improving burn rate. However, too wide a gap can cause misfire under heavy load—dyno test or use a wideband O2 sensor to confirm.
Timing Curve Adjustment
The MSD 6AL does not alter the distributor’s mechanical or vacuum advance curves. For best results, have your distributor recurved by a professional to take advantage of the stronger spark. You can often run 2–4 degrees more initial timing without detonation because the powerful spark allows a fast flame front.
Retarding Timing for Nitrous or Boost
If you use nitrous or boost, the MSD 6AL can work with an optional timing controller (MSD Digital 6AL-2 or separate module) to retard timing automatically. The base 6AL does not have this capability, so plan accordingly.
Comparison: Stock Ignition vs. MSD 6AL Performance
To quantify the difference, here is a side-by-side comparison based on typical measurements from a 350ci small-block Chevy on a chassis dyno:
| Metric | Stock Electronic Ignition | MSD 6AL |
|---|---|---|
| Peak spark energy (mJ) | 35–50 | 110 |
| Spark duration (degrees of crank rotation at idle) | ~10° | 20° (multi-spark) |
| Maximum supported rpm (with stock coil) | 6,500 | 12,000+ |
| Idle quality (vacuum at 750 rpm) | 14 inHg | 15–16 inHg |
| Horsepower (peak, no other mods) | 315 whp | 328 whp (+13) |
| Fuel economy (cruise, highway) | 22 mpg | 24.5 mpg (lean burn allowed) |
These figures illustrate that the MSD 6AL not only adds power but also improves efficiency—a double benefit often overlooked by enthusiasts.
Pairing with Upgraded Coils and Distributors
To maximize the MSD 6AL, consider complementary upgrades. The MSD Blaster 2 coil (PN 8203) is a budget-friendly option that works well with the 6AL. For high-performance applications (boost, high compression), the MSD Street Fire coil or Blaster SS offers lower primary resistance and faster rise time.
For distributors, the MSD Pro-Billet (standard or Ready-to-Run) eliminates the factory module and provides a precise magnetic pickup. If your stock distributor has a lot of wear (bushings, slop in the shaft), a new distributor ensures stable timing. The Ready-to-Run distributor integrates its own module and wiring, making hookup to the 6AL even simpler.
For vehicles with Bosch-type or Pertronix ignition that are not magnetic pickup, MSD offers an adapter harness (PN 8879) to convert the signal to proper trigger levels.
Long-Term Reliability and Maintenance
MSD 6AL units are known for lasting many years. The epoxy-sealed design resists vibration and moisture better than many factory modules. However, the power wire connections can corrode if exposed to salt spray—apply dielectric grease to all connectors. The rev limiter chip is easily replaceable if you change your engine’s redline.
Typical wear items: spark plugs may need to be changed more often if you run a very wide gap because the intense spark erodes the electrodes slightly faster. Use high-quality plugs such as NGK V-Power or AC Delco R42LTS. Spark plug wires should be inspected for carbon tracking every 20,000 miles.
Cost-Benefit Analysis for Different Use Cases
Daily Driver / Street Cruiser
For a mild street car, the upgrade improves drivability, cold starts, and fuel economy. The cost of $400–$600 can be recouped over 30,000 miles of driving via better fuel mileage alone (assuming a 2 mpg gain and $3.5/gal). The improvement in throttle response makes driving more pleasant.
Weekend Warrior / Drag Racer
For a car that sees strip time, the MSD 6AL is almost mandatory. The rev limiter protects the engine from over-rev during missed shifts, and the high-rpm spark ensures consistent ETs. The potential 0.2–0.4 second improvement in quarter-mile time justifies the cost immediately.
Towing / Heavy Load
For trucks or SUVs that tow, the stronger spark helps maintain power under load and reduces the chance of spark blowout. However, the installation must be weatherproofed; mount the box inside the cabin or use a waterproof cover if underhood.
Frequently Asked Questions
Will the MSD 6AL work with my factory computer (ECU)?
Generally, yes, as long as your ECU controls spark through a separate ignition module. The MSD 6AL will replace the module but still receive the trigger signal from the ECU. For distributorless (DIS/COP) systems, an MSD 6AL is usually not compatible without significant rework.
Do I need to upgrade the alternator?
No. The MSD 6AL draws about 2–4 amps continuous, with peaks up to 8 amps. Most stock alternators supply 60–100 amps, so this is a negligible load.
Can I keep my factory tachometer?
Yes, but you may need an adapter if your tach is driven by the coil negative pulse. The MSD 6AL has a dedicated tach output terminal (grey wire). Use that to connect to your tachometer signal input.
Conclusion
Upgrading from a stock ignition to an MSD 6AL is one of the most cost-effective performance modifications you can make. It delivers tangible power gains, improved fuel efficiency, and peace of mind with its built-in rev limiter. The installation is straightforward for anyone comfortable with basic wiring, and the long-term reliability of the CDI design means you can “set it and forget it.” Whether you’re building a daily driver, a weekend track car, or a high-horsepower street beast, the MSD 6AL will unlock performance you didn’t know your engine had. For further reading, check out MotorTrend's installation guide and Hot Rod's dyno test results for real-world data.