The Pro-Billet MSD HEI distributor picks up where the originals left off. Drawing on years of high-performance ignition experience, MSD engineers created a unique ignition module and internal coil that are capable of running above 9,000 rpm. Stock and other aftermarket modules lose spark energy at about 4,500 rpm. These modules produce 50 percent more current than stock units, and deliver a much more precise timing signal as well as more dwell control. The coil delivers over 100 millijoules of energy across the plug gap. For strength and high rpm stability, the QPQ-treated oversized shaft is guided by a sealed ball bearing on top and long sintered bushing at the bottom. The QPQ coating provides a low-friction coating on the shaft and also makes it highly resistant to corrosion. TIG welded to the top of the shaft is an adjustable mechanical advance assembly. The MSD 8375 distributors are supplied with extra springs and stop bushings, so you can tailor an ignition curve to match your driving needs. The advance assembly features chromoly weights that slide on nylon pads for smooth timing advancement through the entire rpm range. There is also a vacuum advance canister to improve economy while cruising. All of these features are enclosed in a great looking, billet aluminum housing that is CNC-machined for accuracy and incredible strength. The MSD HEI distributor comes complete and ready to drop in with a high-quality rotor and cap with brass terminals for great spark transfer. Simply connect a 12 V source to the MSD 8375 distributor and you're up and running. They're designed to replace GM HEI distributors that use a 4-pin ignition module.