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Just got a SN89 head unit w/6 rib pulley and I just want to put out low boost. The pulley on the head unit measures 4" o.d., is this a stock head unit pulley? Would I also combine that with a 6" crank pulley to keep boost somwhere between 5-7lbs. ? Would these 2 pullies keep me at safe blower rpm levels? This is going on my 93GT mustang w/ported stock heads,Typhoon upper/lower intake 65mm tb, 73mm maf, 30lb injectors, Steeda 18 cam.
I am surprised nobody has responded to your question. You should be fine w/ a 4" pulley on the charger. See the spreadsheet on this site:
http://www.superchargerhelp.com/showthread.php?t=4907
I have an '86 Mustang and am running the 3.75 Dia. pulley. Your '93 does NOT have forged pistons (in case you didn't know that already).
A standard SN89 head unit will max-out at about 5psi-5.5psi of boost.Quote:
Originally Posted by steel1
I don't think there is such a thing as a "stock head unit pulley" size. Pulleys are available in a number of different diameters and are sized for specific applications. With the pulley combination you have (4"dia blower pulley and a 6" dia. crank pulley) you'll be running the SN at close to it's optimum impeller speed (39,000-40,000rpm) at around 6,000rpm. If you reduce the head unit pulley size to a 3.75" dia. or even a 3.33" dia., you'll reach the optimum impeller speed at around 5,000rpm. Spinning the head unit any faster will produce very little additional boost (if any) but will increase discharge air temperature substantially, which will only serve to shorten the intervals between fluid changes in the supercharger.
Hope that helps.
The 4" and 6" pulley is the stock pulley size for a Mustang 5.0 and 5# of boost. You will need to be careful with high rpm 5k+ with only 30# injectors and No FMU with your combination of parts.
My bad speedystang forgot to mention I have an fmu w/6:1 ratio. I know a tune is the optimal way to go, but not in the budget right now. This car only sees about 750-1000 nice weather miles per year. Thanks for the info everyone looks like I have to locate a 6" crank pulley