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Inside MSD’s Ready-to-Run Distributors

By: Todd Ryden | 11/17/2020 < Back to Motor Life Home
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As nice as fuel injection, programmable ignitions, and transmission controls are, sometimes it’s nice to keep things simple. In the case of our old ’40 Ford Tudor, simplicity and lack of any modern amenity is looked upon as a relief, but that doesn’t mean we’re cutting corners on the ignition system. For a hot spark, stock looks and easy timing adjustments, we turned to MSD’s Ready-to-Run Distributor.


One of the first things that drew us to the Ready-to-Run was its size. It has the same width as a stock GM points distributor which means it doesn’t interfere with the firewall like the larger HEI distributors from the ‘70s. As for spark output, the distributor has a high output ignition module built into the base of the billet aluminum housing which delivers a powerful spark to improve performance of your engine.


There’s more to the Ready-to-Run than its high energy sparks and shiny billet appearance; it also has an adjustable mechanical advance assembly. When it comes to ignition timing, nearly every application is different and being able to adjust the timing as rpm increases is a big part of the drivability of your ride. MSD developed a mechanical, sometimes called centrifugal, advance assembly that is easy to adjust and set to match your application.


Right on top of each Ready-to-Run Distributor you’ll find the mechanical advance assembly which is made up of weights and a weight plate, two springs, and a stop bushing. The springs control the rate of timing advance as the weights spin outward due to centrifugal force as the engine accelerates. MSD supplies three different sets of springs which allow you to set a very slow rate of timing advance (heavy springs) or a very quick rate (lightweight springs). Using a combination of the different springs produces a variety advance rates.


The mechanical advance is easy to adjust to your specifications with the supplied springs to control the rate of advance and different diameter stop bushings to set the total advance allowed.


To control how much timing advance is allowed, there are six advance bushings supplied, each is a different color and diameters. A 21° bushing is installed from the factory and MSD provides a 28°, 25°, 23°, 19° and 18° bushing in the parts bag. We chose to leave the 21° bushing in place as a starting point. We usually run about 12° to 14° BTDC at idle, and with 21° for mechanical timing at higher rpm that puts our total timing at 33° - 35°. If the engine experiences detonation, we’ll put the larger 23° in to lower the total timing a couple degrees.


Our mild small block in a lightweight street rod can use a quick rate of timing advance so we removed the heavy, slow springs that are installed from the factory in favor of the lightweight (quick) springs. Note the little spacers on the weight studs – make sure they’re in place!


The Ready-to-Run also has a vacuum advance canister which is primarily used to improve economy while cruising down the highway. At a mild cruise speed, there is not much load on the engine which creates vacuum. The canister connects to a vacuum source and will advance the timing during these mild cruising speeds. As soon as you accelerate, vacuum drops and this extra advance stops. MSD’s vacuum canister will advance the timing about 12° at 15in-Hg. In many applications, the vacuum advance is not used and MSD even supplies a lock-out plate with the Ready-to-Run.


The total advance allowed by the mechanical advance is also adjustable with these stop bushings. A 23° bushing is installed from the factory which we left in place. Combined with our set mechanical timing (idle timing) of 12°, that gives us a total timing setting of 35° BTDC which should be right on target. If we run into detonation at higher rpm, we’ll install the 19° bushing.


Wiring the Ready-to-Run is a breeze with a three-wire harness that includes ground, coil negative and coil positive (12 volts). It is very important to make sure your application supplies a full 12 volts to the distributor and coil. Many older cars and trucks could have less voltage available due to original resistor wiring. Also make sure there are 12 volts on the coil positive terminal during cranking and with the key in the run position. In some applications with original wiring, a relay may be the best option to ensure a full 12 volt source.

We installed the Ready-to-Run in a typical small-block Chevy in our ’40 Ford sedan. The smaller housing easily cleared the factory firewall and we stuck with an older points style cap to retain the vintage hot rod vibe of the car. With the new wiring harness in the car, we confirmed a full 12 volts at the coil and for the distributor during cranking and while running. Also, we set the built-in rev limiter at 5,600 rpm which you can read about in the sidebar below.

MSD offers the Ready-to-Run for nearly any domestic V-8 engine including Buick, Olds, Pontiac, Ford, Mopar engines and popular vintage engines such as the later Flatheads, Y-Blocks and early Hemis.


The Ready-to-Run also has a vacuum advance canister which is primarily in place to improve cruising economy. If you chose not to use the vacuum advance, it can be removed and replaced with the supplied lock-out bracket.


A sealed 3-terminal wiring harness is supplied to ease installation. Orange connects to coil negative, red to positive (where it will also receive switched 12-volts), and the black wire is ground to connect to the block or heads. The gray wire is an option tach output.


The gray wire serves a couple different purposes. First, it supplies a filtered, clean 12-volt square wave signal which is ideal for tachometers or to trigger an EFI system such as the MSD Atomic or Holley’s Sniper and Terminator systems. Another feature is to set rev limit for your engine which is explained further in the sidebar of this story.


Be sure to install the new gasket on the distributor housing and apply a liberal amount of the supplied break-in lube to the distributor gear before dropping the distributor in place.


MSD supplies their own proprietary distributor cap which is equipped with HEI style terminals. If you’re swapping from an old socket/points style cap, you’ll need to update the plug wire terminals (available as PN 8848). In our case, we’re going for an old-school look and installed a vintage points style cap.


Ready-to-Run Rev Limiter

As mentioned, the Gray wire of the Ready-to-Run Distributors has two jobs; one is to trigger a tachometer or an EFI system through its filtered 12-volt square-wave signal. Its other use is to set an rpm limit to save your engine in the event of driveline failure or a missed shift. MSD has offered rev limiters for years, but they’re usually set through rotary dials or plug-in modules. Since the Ready-to-Run distributor doesn’t have either, MSD got creative in how to set the rpm. To set the rev limiter, the engine must be revved up to half the amount of the top rpm, then the gray wire must be held to ground for a moment. For example, if you want to program a 6,000 rpm rev limit, you would rev the engine up to 3,000 rpm and hold it there while you (or an assistant) ground the gray wire for a second. When the wire is grounded, the tach will go to zero, and when released, it will display the rpm limit (6,000 in this case) for two seconds. It’s just that easy!

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