Spark delivery is paramount when comparing Distributor And Distributorless Ignition Systems. This article delves into the intricacies of each system, examining critical factors like voltage capacity, rotor phasing, advance mechanisms, and triggering methods to provide a thorough understanding of their respective strengths and weaknesses.
Voltage Capacity and Distributor Design
Engine performance hinges on sufficient spark plug gaps. Ionization voltage, crucial for jumping the spark plug gap, depends heavily on fuel mixture density and electrode shape. Higher compression and supercharging necessitate higher ionization voltage, placing greater demands on the distributor to prevent crossfiring or arcing.
Key considerations in distributor selection include spacing between terminals within the distributor cap, terminal-to-body spacing, and the gap between the rotor brush contact and the distributor shaft. At sea level, electrons jump approximately 32,000 volts per inch. A 1.25″ spacing theoretically withstands 40,000 volts, but factors like turbulence and ozone buildup impact real-world performance. Different distributor cap designs exhibit varying crossfire voltage thresholds. For example, a small Bosch distributor cap crossfires at about 28,400 volts, while a Mallory Comp 9000 boasts an impressive 59,000 volts.
Centrifugal and Vacuum Advance: Impact on Rotor Phasing
Centrifugal advance, where the trigger and rotor advance simultaneously, doesn’t alter rotor phasing. However, vacuum advance introduces a rotor phasing shift, reducing the space between the rotor tip and adjacent terminals. This can lead to crossfiring in 8-cylinder engines. Fortunately, 4-cylinder engines, with their larger distributor caps, generally accommodate vacuum advance without crossfiring issues.
Challenges of Multi-Sparking Electronic Ignitions
Multi-sparking ignitions, common in modern systems, present unique challenges. Their prolonged spark duration (often 22.5 degrees of crankshaft rotation) can exceed the narrow rotor tip of centrifugal advance distributors, causing spark jump issues. Vacuum advance distributors typically employ wider rotor tips, sometimes sufficient for multi-sparking. However, using an 8-cylinder multi-sparking system on a 4-cylinder engine doubles the crankshaft rotation to 45 degrees, requiring even wider rotor tips—a challenge no current production rotor tip meets. Modifications, like custom brass rotor contacts, may be necessary to address this.
Distributorless Ignition Systems: Advantages and Trade-offs
Distributorless systems eliminate high voltage routing through the distributor, bypassing crossfiring concerns. However, they require multiple ignition coils and a more complex triggering and advance system. Cost-saving measures like the wasted spark method, employed in systems like the Compufire DIS IX, fire two spark plugs in series with reversed polarity on one, potentially compromising performance.
The ideal distributorless system utilizes one coil and ignition per cylinder, coupled with high-quality components and a precise triggering system. However, the performance advantage over a high-quality distributor system remains debatable without rigorous comparative testing.
Triggering Methods: Crank Triggering vs. Distributor-Based
Crank triggering offers superior stability. However, using a distributor for high voltage distribution in a crank-triggered system reintroduces the potential for crossfiring. Electronic advance distributors with small caps and insufficient rotor tip width further exacerbate this issue. Crank triggering with electronic advance based on RPM and vacuum input shows promise but increases complexity. Conversely, conventional distributor bodies, when in good condition, provide a simpler, reliable triggering mechanism.
Conclusion: Quality Over Topology
Ultimately, component quality trumps system topology. While distributorless systems offer theoretical advantages, their complexity and potential performance compromises must be weighed against a well-designed distributor system. The choice depends on specific application requirements and performance goals. A meticulous evaluation of component quality and design within each system is paramount for optimal engine performance.
