If you’ve been reading HPP for any length of time, you likely recognized the importance of spark advance. Over the years we have reported through dyno and/or dragstrip testing the benefits of optimizing the advance curve. We’ve found that a variance of even 2 degrees can affect horsepower and torque by several units. So when it comes to attaining maximum performance from your particular Pontiac, you simply need to know exactly what’s going on inside your distributor.
MSD is an ignition-system industry leader. Its multi-spark discharge boxes and high-end distributors are the choice of many professional engine builders of all makes. MSD has been producing two specific Pontiac distributors in its Pro-Billet line for several years, and they remain very popular. Featuring billet construction and high quality internals, each also contains a fully adjustable centrifugal advance system that’s amazingly simple and very user-friendly, and prevents any unexpected advance at very high rpm.
The instructions that MSD supplies with its distributors (also available at www.msdignition.com) contain several charts and graphs that plot the centrifugal advance curve for every possible combination with the kit. Generally known for its quality and accuracy, we had no reason to doubt MSD’s claims, but having seen the effects minor variances can have on horsepower and torque, we simply wanted to verify MSD’s accuracy to ensure our tuning efforts are extracting maximum potential from our Pontiac.
Using our Allen Syncrograph distributor tester and Ready-To-Run distributor from MSD, we assembled each combination to verify exactly how much centrifugal advance each limiting bushing provides, as well as the effects each spring package has on the rate. As expected, MSD’s information is remarkably close to the actual amounts the limiting bushings provide, as well as centrifugal advance rates from the spring packages. Here’s how it shakes out.
MSD offers two different top-quality distributors for the Pontiac V-8. Its PN 8563 Pro-Billet contains no vacuum advance and requires an external control box, while its PN 8528 Ready-To-Run unit is a simpler, plug-and-play design. Still readily available new, it’s not uncommon to find used units in excellent operating condition for sale at swap meets and Internet-based classifieds.
The centrifugal advance system found in MSD’s distributor is based on a typical GM-points type design. As engine speed increases, the weights fly out from centrifugal force, which advances the firing position of the internal reluctor. MSD installs two heavy springs that provide the slowest advance rate at the factory, but they’re easily replaceable, allowing you to determine the rate that works best for your particular combination.
With each distributor, MSD supplies a complete centrifugal advance curve kit that contains a number of springs and limiting bushings. It allows hobbyists to easily “recurve” their distributor to improve the performance of a given combination. Oftentimes the kit is no longer with the distributor if purchased used. Fortunately, MSD sells it separately (PN 8464) for less than $15.
We used a professional distributor tester to verify the rate and amount of centrifugal advance, which each spring and bushing combination provides. The arrow illuminates each time the distributor fires. It gives the effect of eight arrows as it rotates. Following its progress on the graduated degree wheel accurately provides the amount of centrifugal advance at a given rpm.
The limiting bushing is secured to the advance pin by a small nut. It’s removed using an 11⁄32-inch open-end wrench. Once the nut and its washer are off, the bushing should slide out with little persuasion.
MSD installs the blue bushing during assembly. Installation of any other limiter can be performed in minutes. Since the bushing alters how far fore and aft the advance pin travels in its slot, be sure to verify your initial setting and re-adjust as necessary. On our street-driven Pontiacs with cast-iron heads, we generally shoot for 11-12 degrees of initial timing and 25 degrees of centrifugal advance to arrive at 36-37 degrees of total. Vacuum advance would be over and above this amount. Total timing for aluminum heads may vary.
Modifying the rate of advance is as easy as installing new advance springs. On a naturally aspirated Pontiac V-8 that operates suitably on pump gas, we prefer an advance curve that starts around 1,200-1,400 rpm and reaches maximum advance between 3,000 and 3,500 rpm. It’s quite acceptable to mix and match springs of different thicknesses and/or tensions to achieve the specific rate that works best for your Pontiac.
The chart above reveals the specific engine speed at which the distributor begins to advance, as well as when it reaches maximum advance with a 21-degree limiting bushing installed. Since the black bushing reduces travel, the rpm point that maximum advance is reached is reduced by about 100. The silver and red bushings increase travel, thus delaying maximum advance by no more than 200 rpm.