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 |