Can I safely go to a smaller pulley on my SN89?

I'm running an SN89 on my 5.0L Mustang. Under ideal conditions I see about 5psi boost with a 4.5" diameter pulley. With a shift point of 6,000rpm can I safely go to a smaller pulley to increase the boost?

If so, what is the smallest size/max boost I can use without harming the internals of the blower? Also where can I purchase a smaller pulley?

Any help would be greatly appreciated.

I have heard that the sn blowers can handle between 38k-41K impeller speed. MY sn2000 came with a 3.25 s/c pulley and a 6.5 crank pulley. I shift @ 5500 stock. Determine your impeller speed; Crank pulley size x 4.4 supercharger ratio x rpm / supercharger pulley size = impeller speed. On my setup, I was spinning my impeller with no problems up to 48K. Now, with teh sn impeller's. THey only flow 850fcm and after 8psi, they just heat the air and do little good after 8lbs of boost. Either get a smaller pulley that will set you @ 8psi, or get the VR4.

Thanks for the reply. I'm having trouble measuring my stock crank pulley on the car. Is there a standard size that would have come with the SN89 5.0L kit?

OK I have a 4.5" on the blower and 6" on the crank. So going by the equation that gives me 35,520 impeller speed. Can I safely move to a 4" blower pulley = 39,960??

What kind of boost increase will I see? Will I need a new belt? Any downsides to this set-up? (I run the fluid cooler and change the Type F religiously)

yep! I spin my unit up to 48000 rpms and have rarely had a problem with it.