[mrclean27_72]

Originally Posted by StangMan

I believe it should have a metal tag on it also that has the model number and stuff. If not, it looks like an SN 89, the SN 92, or SN 93 unit... although the label's color isn't the typical blue so I am not sure. In any event, the SN ball drive units made 5 PSI with the 4.25" pulley they came with. You could overdrive the units with a 3.75" compressor pulley to make 7 PSI or a 3.5" pulley to make 8 PSI. That is at 5500-6000 RPM. Spinning the motor to 6500 RPM you might see another pound of boost. When I ran my older 302 combination with an SN unit and a 3.5" pulley I made 9 PSI at 6500 RPM. However, you have to be very careful not to over rev the ball drive units because they are known to break if you do. Therefore, a lot of people avoided using the 3.5" pulleys and ran the 3.75".

Also, there was a later ball drive type "race" unit called a VR4 that made 13-15 PSI (I believe). I am not sure what size pulley it used though.

Btw, does it have a six rib pulley on it?

What size crank pulley? and injectors?