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Without spark, you can’t create a fire. The air/fuel mixture in an automotive engine depends on a high-quality spark, and in older cars, that isn’t always a given – the points-style distributors and external ignition systems don’t have nearly the consistency and dependability as the ignition systems found in newer vehicles on the road today.
Performance Distributors’ D.U.I. all-in-one ignition system solves a number of issues facing older hot rods. The built-in Dyna Module offers longer dwell times for increased spark energy.
The motivation for this article is a 1965 K-Code Mustang fastback that is basically stock except for a new short block, hydraulic cam, Weiand intake and Street Demon carb. The nearly 50-year-old mechanical-advance distributor wasn’t holding dwell as consistently as the new carb was feeding fuel, so an all-in-one Street/Strip D.U.I. Distributor from Performance Distributors in Tennessee was ordered.
What Is It?
What is D.U.I., you ask? Davis Unified Ignition, which provides everything needed for the ignition system contained in one unit – the distributor, ignition coil, and vacuum advance module are all built into one easy-to-install unit that provides all the spark we’ll ever need to light this puppy off.
The D.U.I. is based on the High Energy Ignition system developed by Delco-Remy back in the early 1970’s, and consists of the internal control module and magnetic pickup housed in the distributor. By eliminating the ignition points and coil wire, reliability and consistency are introduced.
How Does It Work?
Performance Distributors developed the D.U.I. to provide the spark that older hot rods need. Unlike traditional multi-spark ignition systems that use a capacitive discharge external ignition boxes, the D.U.I incorporates Performance Distributors’ Dyna Module. The Dyna Module has an electronically-programmed high dwell that will increase the coil saturation time, which allows the the coil to produce one long-duration spark instead of several shorter multiple sparks.
Left - The D.U.I. distributor has the ignition coil built right in - it sits atop the cap much like an older GM HEI ignition system. Right - The distributor arrives with a steel camshaft gear for long life and compatibility with older cast-iron hydraulic and flat-tappet camshafts.
That single long-duration spark is designed along with the internally-housed 50,000 volt coil to improve throttle response and low end power – which is exactly what the majority of street-driven hot rods need. Nobody wants to fire up their pride and joy for cruise night and have it pop and sputter down the road.
“Our theory is that if you produce a longer duration spark initially, then multiple sparks are not necessary. By increasing the dwell in the module, that in turn lets the coil saturate longer to build up a more intense spark. We’re increasing the dwell 2-3 degrees from idle to about 3,000 rpm, and then it maxes out at about 36-38 degrees of dwell there and maintains it through the rest of the rpm range,” says Steve Davis, Performance Distributors’ president. “It works in conjunction with the coil’s ability to produce a hotter spark through its increased windings and larger diameter wire. The result of that is that the customer gets to open the plug gaps wider to take advantage of the better spark to burn a larger percentage of the fuel.”
By housing the coil on top of the distributor cap, it simplifies the process of installation to a true one-wire connection. And the coil’s high voltage characteristics allow spark plug gaps to be opened to as much as .055-inch, providing a large spark kernel to light the air/fuel mixture. Oil-impregnated bronze bushings are used at the top and bottom of the distributor to allow the D.U.I. to provide accurate ignition trigger signals.
If you’ve got an aftermarket camshaft installed, you know that startup and idle are important as well, as some of the bumpsticks on the market can cause idling issues no matter how good you are at carburetor tuning. The D.U.I. cures that in many instances by combining the large plug gap with the longer spark duration to ensure complete combustion – no more raw, unburnt fuel out the tailpipes. In addition, a vacuum advance module is mounted to the side of the distributor to help provide better fuel economy as well as helping to keep the spark plugs clean for longer life. Advance should be set with the line disconnected and plugged.
There are a pair of bronze bushings, one at each end of the distributor, to ensure accurate spark triggering. Vacuum advance is also provided for smooth idling properties and good street driving characteristics.
Performance Distributors goes the extra step of calibrating the distributor for your particular engine combination using a Sun Distributor Machine, providing a special weight and spring assembly that is hand-fitted. This results in a timing curve that matches what your engine needs to provide instant throttle response and maximum power. You’ll need to provide information about the vehicle and engine such as cam duration and lift, compression ratio, carburetor size, vehicle weight, maximum rpm, transmission and octane of fuel.
We’re able to change any part of the distributor to get the customer the best part for their needs. – Steve Davis, Performance Distributors
“Our know-how comes from years of experience with different camshafts and compression ratios. We make all of our own springs and advance weights – everything is made specifically for our distributors. Every purchase is assigned an individual ID number, so if a customer changes camshafts, or pistons in the future, or wants to put their distributor into a different engine, they can call us with the ID number and we’ll be able to discuss whether they need to send the distributor in for a re-curve,” says Davis.
The Install Specifics
Installation is easy – when we say easy, we mean really easy. Simply remove the old distributor cap (and vacuum advance hose, if applicable) and the distributor hold-down clamp and bolt. Use a ratchet and socket to spin the engine until cylinder #1 is at TDC at the end of the compression stroke, then make a small mark on the manifold where the rotor points. This a good time to double check the TDC mark on the balancer, as well. Pull the old distributor up and out.
Left - The first order of installation business was to set the engine at top dead center. Middle - Once we had it rolled over, we marked the harmonic damper at 0 degrees to make our timing chores at the end of the installation easier. Right - We also marked the position of the rotor on the intake manifold for reference.
The new D.U.I. Distributor installs just as simply as the old distributor came out. Position the rotor towards the mark on the manifold and slide the distributor back in, making sure the rotor turns towards its original position as it drops into place. At this time, you need to ensure that the oil pump drive rod engages properly into the bottom of the distributor – the hardest part of the entire job.
If it engages, the distributor will drop right in and rest on the flange. If it doesn’t, you may need to wiggle the rotor to get it to seat properly. Make sure that your rotor is pointing at the mark you made earlier, reinstall the hold-down clamp finger-tight, and put the cap on the distributor. Transfer your plug wires at this time.
After dropping in the D.U.I. distributor, lightly tighten the hold-down clamp and then set the timing as instructed.
Atop the distributor, the coil cover has just two connecting terminals; one marked BATT, and the other marked TACH. Other notes to consider – if you are converting from a breaker-points distributor, or a stock Ford electronic distributor, you must eliminate any ballast resistors to provide full alternator voltage to the D.U.I. From your ignition switch, run a 12 gauge wire straight to the BATT terminal on the distributor cap to provide a hot lead. On the tach side, 18 gauge wire is sufficient to provide a signal.
Left - Making the electrical connection is simple - one wire powers up the whole works, and the connections for the module are self-contained. Right - High-quality crimpers come in handy here, as you don't want to be chasing a poor connection in the future.
Performance Distributors recommends setting the initial timing at 12 degrees of advance. Reconnect the vacuum hose, and away you go! Make sure to follow their explicit directions regarding setting the timing, as they have a few notes that will help your car to idle properly. There are also a number of troubleshooting ideas in the installation manual that are very helpful.
Live Wires
With the upgraded spark energy, we’d be remiss if we didn’t feed the engine with a quality set of spark plug wires, so we turned the page in the Performance Distributors catalog to check out their Live Wires.
Live Wires are custom-built, 8mm, spiral core ignition wires that provide low resistance and high spark energy transmission.
The Live Wires line of spark plug wires offers low resistance with high temperature resistance – two features that are critical in a hot engine bay filled with a performance engine making lots of horsepower. Live Wires use spiral core, silicone-jacketed 8mm wire that’s covered by a non-flammable heat treated fiberglass braid. Spiral core wire also provides excellent radio suppression characteristics that ensures your radio won’t have that annoying whine – and they still work great for you racers using delay and stutter boxes.
Left - We gapped our spark plugs at the recommended .055-inch to take advantage of the increased spark energy from the D.U.I. Right - Make sure to use the supplied dielectric grease on both the distributor cap and the spark plug terminals to provide good contact and ease of removal.
The spiral-core wire has a stainless-steel wire that’s wrapped around a magnetic core, offering low resistance in the neighborhood of 300-350 ohms per foot to allow the spark to easily travel from the coil to the plug. Heat protection to 1,400 degrees Fahrenheit is standard, as is resistance to moisture and chemicals.
Our know-how comes from years of experience with different camshafts and compression ratios.–Steve Davis, Performance Distributors
The plug wires are cut-to-fit for your particular engine, are numbered on both ends for ease of identification, and the kit even includes dielectric grease that prevents voltage leakage. The grease also provides the added benefit of preventing the boot and terminals from sticking to the plug, meaning you won’t pull them apart the first time you try to change the plugs.
If you’ve got a non-standard application that requires custom-fit wires, just give Performance Distributors a call, and for an extra ten bucks, they’ll build whatever you need.
In Use
The proof is in the pudding, as they say. Starting improved and timing advance appears more consistent. The vehicle owner also noticed that the spark plugs were cleaner after a couple hundred miles. Dyno tuning and testing are planned for the future, so we’re expecting optimum performance with less hassle.
