2

INSTALLATIONINSTRUCTIONS

PULLEY SIZE AND RATIO

The MSD DynaForce 120 and 160 Amp Alternators are supplied with a single groove V-belt pulley.

MSD offers a dual V-belt and a 6-rib serpentine separately. Also, if you require a special pulley, the

shaft of the alternator is a common 17mm shaft that will accept some other pulley systems.

The pulley supplied has a diameter of 2.80” and a 3:1 pulley ratio is recommended for the street. (As

an example, when your engine is at 1,500 rpm, the alternator should be at 4,500 rpm.) The DynaForce

Street Alternators can handle up to 18,000 rpm maximum. They are most efficient when operating at

about 2,400 alternator rpm and function best between 2,400 and 7,500 alternator rpm.

Figure 2 Alternator Dimensions.

2”

4.33”

5.98”

TO FRONT OF SHAFT

5.12”

6.61

Keep in mind that underdrive crankshaft

pulleys can affect the output of your MSD

alternator at idle and lower rpm ranges.

Therefore, underdrive pulleys are not

recommended for street use.

INSTALLATION

The DynaForce Alternators listed at the

top of these instructions are designed for

use in applications that require straight

mounts from top to bottom. Notice that the

two mounting tabs are 180° apart. This is

a common configuration for GM vehicles

used from the mid 1960’s through the mid

1980’s. Check to confirm that you have the

proper mount for your application before

disassembly (Figure 2).

Mount the DynaForce using the factory

hardware. Do not tighten the bolts entirely

at this time. Once mounted, it is important

to check the alignment of the pulleys. Place

a straight edge on the water pump or crank

pulley to the alternator pulley. If they are not

Crankshaft Pulley Diameter

Alternator Pulley Diameter

= Pulley Ratio

Pulley Ratio X Engine RPM = Alternator RPM

EXAMPLE:

EXAMPLE:

8.75"

2.8"

3.1 X 800 = 2480 Alternator RPM

= 3.125 Pulley Ratio

aligned, the alternator may require shimming. Also, note that some aftermarket brackets only have

one solid mounting point such as systems that incorporate a turnbuckle or heim joint for tension

adjustments. MSD recommends a secondary support to dampen vibration.

Note: If you are using anodized or powder coated brackets, it is recommended to connect a ground

wire from the alternator housing to the engine block.