When it comes to Mopars, there's a good choice of quality aftermarket ignitions available. In the past 30 years, enthusiasts have been swapping stock single point to dual-point distributors, using distributors like the Mallory Unilite, Mopar Performance electronic, MSD Pro Billet with a 6AL box, and recently, the D.U.I. HEI distributor has been brought into the mix. When we heard that Performance Distributors had just released eight new HEI-derived distributors for B/RB power plants, we had to give one a try. Our test engine would be our RBRE (Ray Barton Racing Engines) 493 wedge, ("Long Armed Wedge," June & July '03). We wanted to find out if the D.U.I. distributor was as good as they claimed.
Performance Distributors developed these 383/440 distributors to clear stock valve covers and fit under low production hoods like our '67 Coronet's. We tried a set of the Mopar Performance finned aluminum valve covers, but in order for them to fit under the D.U.I unit, we would have needed to clearance grind the distributor and MP valve cover by an 11/48 inch on each, so keep that in mind. These brand new units are precision built, blueprinted, and curved on a distributor machine to match your combination.
We have to face facts, and give the GM HEI (High Energy Ignition) distributor some recognition as one of the best OEM electronic distributor produced back in the '70s and '80s. The fatter/wider distributor reduced spark scatter between the terminals, which lead to a smoother running engine. A stock HEI would start to misfire due to voltage drop from the coil around 5,000-5,500 rpm. PD (Performance Distributors) reworked the HEI with their 50,000-volt D.U.I. coil and Dyna-Mod module, so voltage doesn't drop off until around 7,500 rpm for their street/strip coil, and 9,000 rpm with their racing coil. The Dyna- Mod module has more "electronic dwell" for extra coil saturation time. This special module helps the coil produce a more intense spark to the plugs (spark plug gaps can be opened to .055-inch and plugs stay cleaner longer).
The D.U.I. distributor features a cap and rotor with 50-percent higher dielectric strength to handle extra voltage, and all-brass terminals for maximum conductivity. This one-piece ignition system (everything is contained within the distributor) needs only one 12-volt wire to hook it up and you're ready to run. The D.U.I. eliminates the messy wiring found on stock electronic and spark-box-type ignitions. Also, without a coil hanging around, the engine compartment has a cleaner look.
For our test, the D.U.I. would be facing a performance ignition that had been performing flawlessly for the past 10 years or so.
Our friends at SLP Performance Parts welcomed the R/T to a good flogging again on their chassis dyno. We were anxious to try the D.U.I. distributor on the 493 stroker. For our baseline pull, the horsepower was 504, and torque was at 510 lb-ft. Our carb's jetting was on the money, with the air/fuel mixture at 12.6 at WOT (wide open throttle), and 14.7 at idle and steady cruising speed. Timing was set at 39 degrees total. We tried other settings with the timing, but 39 turned out to be the magic number.
After the baseline dyno flog, all of the ignition components and wiring were removed. We used the stock 12-volt wire, that originally juiced the positive side of the coil, to power the D.U.I. distributor. The original ballast resistor that hung on the firewall was bypassed. This allows sufficient voltage to power the distributor. LiveWires plug wires were used, and Performance Distributors custom-made them 4 inches longer for our application because the D.U.I. HEI distributor is 3 inches higher than our previous unit. The LiveWires plug wires are numbered on each end for the cylinder, and incorporate a spiral core and a unique sleeving for protection up to 1,400 degrees.
Comparison time was nearing for the fatboy distributor as it was dropped in place. The timing was set at the same 39 degrees total. The wedge seamed to have a smoother idle and rev-up faster. With the R/T still strapped down, the moment of truth came when SLP's Hank Deniecki smashed the pedal down. We were stunned to learn we had picked up 7 ponies at slightly above 5,000 rpm. But here's the kicker-we gained 14 hp at 6,352 rpm. That's where the 727 upshifts at WOT. Also, a solid 10hp improvement was realized from 5,300 to 6,500 rpm. Torque was also up, 8 lb-ft at the same 5,300 to 6,500 rpms.
We fattened the jetting from 88 to 90 on the secondary jets, but the air/fuel mixture didn't differ from the baseline. We thought that if the D.U.I sends more fire into the combustion chambers, more fuel would help. It didn't, and we lost a couple of horsepower. For the next step, we opened the plug gap to the recommended .055-inch-it didn't make a difference either. A wider gap should allow more spark energy to burn the gaseous mix better in the combustion chambers.
With limited dyno-time, we pondered how we could coax more power? We had already messed with the jetting and returned to the original jets (80pri/88sec) and maximum power was restored. Retarding or advancing the timing didn't add any more spin to the rollers. With that, we called it a day. For the ride home, we noticed that the wedge ran smoother and stronger.
Chassis Dyno ResultsSuperFlow SF840SAE-Corrected Rear-Wheel Horsepower and TorqueTested at SLP Performance Parts R&D Engineering Center
| ||Baseline w/MSD ||D.U.I. HEI |
|Max hp/rpm ||504 at 5,193 ||511 at 5,186 |
|Max tq/rpm ||510 at 5,148 ||517 at 5,178 |
|Avg hp 5,000-6,500 ||471 ||480 |
|Avg tq 5,000-6,500 ||442 ||450 |