Whether it’s your first time upgrading your ignition system or you’re such a pro at it by now that your friends call you “Sparky,” you might take some time to catch up on some quick, light reading before you stab in that new Davis Unified Ignition (D.U.I.) distributor from Performance Distributors.

The company has revised its installation instructions to make them more user-friendly.
“Still, we get calls because they just don’t understand or are at their wit’s end because they can’t figure something out,” says Office Manager Brian Caruth. “And most of the time it’s just a simple fix.”

Although Performance Distributors representatives are happy to take your call, if installers would take just a few minutes to check some of the basics, they could avoid some headaches and get their ride up and running more quickly, Caruth says. Caruth, who’s worked for the company for more than 27 years, has fielded many tech calls and still often works the phones. He shared with us what the top five calls are to the tech line.

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Davis Unified Ignition (D.U.I.) distributors include high-output components, such as a high-output coil and a high-dwell module, for snappier performance. The Street/Strip model (shown) provides reliable performance to 7,000 rpm, while the Race unit is intended for those spinning their engines from 7,000-10,000 rpm.

Top Tech Call: “No Fire”

The tech line’s number-one call is for a “no-fire” from the distributor after installation, but the solution is pretty simple, Caruth says. “The first thing we tell them is to check their grounds,” he says. Probably six times out of 10, he says, a “no fire” problem can be traced to a simple problem of a poor ground.

This problem can appear on either a ground-up build or when upgrading an old distributor. “They don’t know if their ground’s still good under there or not,” Caruth explains. “It’s often little things that haven’t been checked out. They may have a loose ground on the engine, paint on the intake where the distributor sits, just a number of things. On rare occasions, they may have to go as far as adding a secondary ground wire to the distributor. In that case, just run it from any point on the housing back to the battery or to the chassis: anything like that, wherever they can pick up a good ground, and that generally cures the problem.”

Make Sure You Have a Full 12 Volts

Keep in mind if you’re replacing an original points-style distributor, you may be accidentally trying to run your new DUI with insufficient voltage. “[Customers] need to use a minimum of a 12-gauge wire, connected to a good switched-12-volt source. A popular spot we tell them to go to is right off the starter solenoid to pick up a hot there.”

With a multimeter, an installer can check that the wire in question is a full 12 volts (with ignition on and cranking) and not part of a circuit with a ballast resistor. “Sometimes they’ll try to use the original hot wire, such as on the old Ford systems, where they had two wires going to the distributor or to the coil. One was 12 volts during startup and then it was through a resisted wire in the run position. They’ll connect the resisted wire to the distributor, but our HEI [High-Energy Ignition]-style ignitions need a minimum of 10.5 volts to run. Anything less than that is not enough to make it fire.”

You need to use a minimum of a 12-gauge wire, connected to a good switched-12-volt source. A popular spot we tell them to go to is right off the starter solenoid to pick up a hot there. — Brian Caruth, Performance Distributors

Each Distributor is Tuned and “Fired” Before Shipping

It’s important to keep in mind that before each D.U.I. leaves the Performance Distributors facility, it is installed and “fired” in one of multiple vintage Sun distributor machines, checked for proper operation, and has its advance curve tuned. So a D.U.I. arriving DOA is rare, according to Caruth.

“I couldn’t tell you how many times we’ve had customers send the distributor back because they claim they’ve done everything that we’ve told them to and can’t get it to fire,” Caruth explains.  “They’ll send it back, but when we put it on the machine, it sparks right off.” That’s the case probably nine times out of 10, he says, in which case, most of the installer’s problems were traced to a bad ground or insufficient voltage.

“On rare occasions, it could be a component has failed by the time they go to install it,” Caruth says. Two of the components can be checked with a simple multimeter: use the meter’s ohms setting to check resistance of the primary (0.6 – 1.5 ohms) and secondary resistance (6.0k – 10k ohms) of the coil. For the magnetic pickup, the desired value is between 800 and 1,000 ohms; as long as it is within that range, it produces a signal sufficient to send through the module, and in turn, fire the coil. “The module is the one component that can’t be tested with a meter. So the installer would have to take it to a parts store, where they can test those.”

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Although failure after leaving the facory and before installation is rare, two of the distributor's components can be checked with a simple multimeter. Use the meter’s ohms setting to check resistance of the primary (0.6 – 1.5 ohms) and secondary resistance (6.0k – 10k ohms) of the coil (left). For the magnetic pickup, you're looking for a value between 800 and 1,000 ohms.

Tech Call Two: Problems With Ignition Timing

The D.U.I. distributors include high-performance components, such as a high-output coil and a high-dwell module. That provides snappier performance, but installers need to be aware of a side effect of increased dwell, which means the coil is energized for a longer period of time. “When they go to time their engine, a lot of the calls we get will be, ‘The timing is just bouncing around all over the place,’ or, ‘I set it at 12 degrees, as you recommended, but this thing just has no power on the low end,’” says Caruth.

“The first question I’ll ask is, ‘What timing light are you using?’ They might say something like, ‘Oh, I’ve got the $800 Snap-On digital timing light,’ and I’ll say, ‘Well you just need to put that back in your toolbox, because it’s not going to work.’ What you need to use is just the standard old-school straight timing light and read it right off the balancer. The increased dwell throws off those high-dollar timing lights. So the timing light may read 12 degrees, but in all actuality, they might have four degrees. And it can go the other way. It could be they’re actually running more timing advance than what the timing light is saying.”

 

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While distributors for small-block and big-block Chevy (left) remain big sellers (caps available in multiple colors,) AMC distributors are currently the number-one seller for Performance Distributors, often destined for classic Jeeps, such as CJ5s, CJ7s, Cherokees, and Grand Wagoneers.

Tech Call Three: What Type of Spark Plugs Should You Use?

With the increased output from the new distributor, some installers wonder if they need to adjust which spark plug they use.
“Really, any type of plug will work fine,” Caruth says. “But one that we recommend because we’ve used it in all our test engines and applications is the Autolite double platinum. They are easier to gap at the wider setting that we recommend.”
Whereas a stock gap may be .035-.045 inches, Performance Distributors advises an increase to .050-.055 inches for more efficient combustion—and power.

“And we tell them to keep the same heat range their engine calls for. All we’re concerned with is opening up that gap to expose more of the spark kernel to the fuel mixture, and that’s where you get the increased burn for the increased performance.” Caruth said that any spark plug can be used, but of course, the platinum plugs will offer much longer wear than a standard plug.

Tech Call Four: Which Source Should I Use for Vacuum Advance: Manifold or Ported?

Another simple tech question fielded by Performance Distributors is where to hook the vacuum advance up. “We generally suggest using manifold vacuum, because that way it’s pulling vacuum at idle, and with the vacuum advance coming in while it’s idling, that generally helps with off-idle performance,” Caruth says.

“It does help with idle quality, and it also helps keep the plugs cleaner for a longer period of time since it keeps them from loading up. Once you crack the throttle, there’s no difference between the two [vacuum sources]; it’s just at idle where it makes the difference.” Caruth also says that, in rare cases, if a caller is having issues such as having an idle that is too high and they don’t want to adjust it at the carburetor, then the company will suggest using ported vacuum.

Tech Call Five: Pre-sale Questions

Not all tech questions are for problems getting up-and-running, though. As we mentioned earlier in this article, all distributors are hand-built and tuned on a Sun distributor machine. “These guys want to know about the distributor before they purchase it, so they’ll call and ask multiple questions, such as, ‘Well, how do you tune the distributor without physically having the engine and the vehicle there?’ The custom tuning is what really seems to get their attention, because that way they don’t have to use multiple springs and a set of weights to try and tune it themselves.”

For distributors sold through “big box” sellers, the company tunes them with a generic advance curve that will work for anywhere from stock to moderately modified engines, Caruth explains. But if the distributor is bought directly from Performance Distributors, it can custom-tune the curve to the buyer’s combination, and at no extra charge.

To dial the distributor in for a customer’s specific combination, Caruth says Performance Distributors representatives ask a series of questions about the engine, including cam duration, valve lift, compression ratio, how much the vehicle weighs, carburetor size, the octane of the fuel that will be run, and whether it’s an automatic or manual transmission.

“That’s a service that we offer that, as far as I know, no other big ignition company does. We make sure the curve checks good, all the electronics are working properly, but they’ll ask how do we know how to tune it when we don’t have the vehicle? That’s how we do it, by using the specs of the engine in the vehicle,” explains Caruth

A related question is whether the company uses adjustable or fixed vacuum-advance types. “We use the fixed vacuum advance cans so there’s no tendency for the adjustments to be lost over time because of vibration.”

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Smooth operation of the mechanical advance is checked after assembly of each distributor. Springs of various strengths are selected to provide the desired mechanical advance as part of tuning the overall ignition advance curve on the Sun distributor machine.

Race or Street/Strip?

If a little more voltage is good for the Street/Strip distributor, even more has to be better, right? Well, not so fast, if you’ll pardon the pun. Caruth says callers to the tech line may be tempted to think of it this way, but it boils down to the intended use of the vehicle.

“If it’s for everyday driving, of course the Street/Strip distributor is going to be more than enough for it,” says Caruth. “A misconception by some of these customers is, ‘Well, the race distributor puts out more power, so wouldn’t that make my engine put out more power? And the answer to that is no. The benefit to the race version is if this engine is going to be pushed over 7,000 rpm.”

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LiveWires spark plug wires are custom-fit for each application. So if you've added tall valve covers repositioned where the lead for the number-one cylinder, be sure to tell your sales representative so you will receive wires with the correct lengths. The Cross-Fire DUI Street/Strip Chevrolet DUI distributor (right, shown without vacuum advance) allows the wires to be routed neatly on each cylinder bank.

The race coil is designed to put out approximately an additional 3,000 to 5,000 volts at higher RPM. “On the low end, there’s no difference in the spark output between the two variants. The race version is only going to be beneficial if they’re running this engine anywhere from 7,000 to 10,000 rpm.”

One last related tech-line question concerns LiveWires spark plug wires, which are custom-fit for each application. “If a customer has done something different, like tall valve covers or anything, or just they haven’t positioned number one where it typically is, then the wire lengths might be off a little bit,” Caruth relates.

“That’s not really a big tech question, but it’s something we get occasionally. If a customer has a specific way they want to route these wires, they can call us up and give us the length that they want for each cylinder, the type of boots they want, and we’ll build the wire set custom for them so that way they know they get an exact fit.”

So if you’re looking for a custom solution to upgrading your ignition system, Performance Distributors can set you up… and provide technical assistance after the sale.