Help With My SN-92???

[ProZac]

hey all i have a SN-92 and i have a half inch smaller pulley on it from the factory. i changed it it ran good for awhile then now i cant get full boost what is about 9psi it goes to 6-7 psi and then drops to 5psi changed belt its tight~ i dunno what wrong with it anyone know hope someone can help me out thanks ~~Zach~

[Dirk Diggler]

Zach,

YOu are over spinning the ball drive. multiply the crank diameter by rpm's x 4.4 (impeller ratio) divide by the diameter of the charger pulley.

4.4 x 5500 x 7 / 4 = 42, 000. YOu do not want to spin the charger over 41k.

Now, my VR4 will bolt on to the back of your sn92. You remove the back plate and impeller and replace it with the VR4. I have a post here of what is included plus a few extras.

Drik

MAKE SURE NOT TO OVERSPIN THE CHARGER!!!!! It will mean a quick death to the bearings.

[ProZac]

5700rpm rev limiter and hit that sometimes~ stock was 4.25 and i got a 3.75 on it now and a 7inch balncer pulley so is my SN-92 is going out? how much to keep my supercharger unit and put everything that came with the VR4 for how much? and ill tell ya what i think~ Zach Thanks~

[Dirk Diggler]

5700rpm rev limiter and hit that sometimes~ stock was 4.25 and i got a 3.75 on it now and a 7inch balncer pulley so is my SN-92 is going out? how much to keep my supercharger unit and put everything that came with the VR4 for how much? and ill tell ya what i think~ Zach Thanks~

Pretty simple. First take the crank dia 7, multiply by rpm 5700, and by 4.4 then divide by the supercharger pulley. so the 3.75 is putting your impeller speed at 46K, a bit over. 4.4x5700x7/3.75

or /4.25 your at the perfect rpm for the stock impeller 41K. If you go to the vr4, 45K is max. NOw, not the balancer pulley but the CRANK pulley. All my calcuations were if you had a 7in crank pulley. NOw if you ahve a 6in or 8 inch crank pulley, that value would change. so the foumula for the impeller speed is;

CRank dia x rpm x impeller ratio (4.4) / superhcarger pulley = impeller speed.
VR4 impeller max is 45K, sn series 41k, I have read that sn's also are only rated at 37K.

Now if your charger is going out, you will hear a whine. IF so, I can easliy walk you thorugh the rebuild process. You can get used bearings which are essentially as good as new. the main thing is the balls. you need them to be new. So if you hear no whine, no worries, but put the other pulley on. Rather be safe than sorry. IF you want my vr4, i have three others who want it. And I have the last VR4 kit available from paradise, actually, brian bought the last one, but his is not for sale, MINE IS.

You need to purchase an inch/lb torque wrench and see what your current ball drive is set at. just go to harbor frieght, get an inch/lb torque wrench for 20-30 bucks. Then, put the wrench to the s/c with no belt on it. It should measre anywhere between 22-44 inch lbs at teh pulley. That way, you will have a reference point when you decide to rebuid teh uint. The torque on the ball drive is 22 inch lbs for sn's and 44 inch lbs for vr4's I would not spend the cash on sending it out and having it rebuilt, do it your self. It is EZ!

As far as you unit needing to be rebuit, no worries unless it is whining. I would take the smaller pulley off to be safe!

[ProZac]

thanks for this info are u craig from pardise wheels??

[Dirk Diggler]

no. same name

[Surgeon]

Now if your charger is going out, you will hear a whine. IF so, I can easliy walk you thorugh the rebuild process. You can get used bearings which are essentially as good as new. the main thing is the balls. you need them to be new. So if you hear no whine, no worries, but put the other pulley on. Rather be safe than sorry. IF you want my vr4, i have three others who want it. And I have the last VR4 kit available from paradise, actually, brian bought the last one, but his is not for sale, MINE IS.

You need to purchase an inch/lb torque wrench and see what your current ball drive is set at. just go to harbor frieght, get an inch/lb torque wrench for 20-30 bucks. Then, put the wrench to the s/c with no belt on it. It should measre anywhere between 22-44 inch lbs at teh pulley. That way, you will have a reference point when you decide to rebuid teh uint. The torque on the ball drive is 22 inch lbs for sn's and 44 inch lbs for vr4's I would not spend the cash on sending it out and having it rebuilt, do it your self. It is EZ!

Sounds like you're the man with the knowledge I'm seeking!!! I've got an SN-93 with fmu & boost retard on my '96 T/A. Low-on-fluid resulted in loud whine. Disassembled unit and found balls were badly pitted. Purchased a brand-new SN-93 via eBay. My unit had modifed impeller so decided to swap into new unit. Problem is: new unit will only make 3-4psi!!! (Original unit made 9-10psi.) I assume problem is ball-torque you mentioned. I guess this is controlled by the number of shims placed under the impeller. (Old unit had 3, new unit had 2 --> I guessed and reinstalled the modified impeller with only 2 shims.) Are these the shims that adjust the ball-drive torque and do more shims behind impeller result in higher torque settings? Also, where can I purchase replacement balls/bearings/seals for my original unit? Also, what is the advantage of the VR-4 unit you have for sale and how much are you asking for it?

Thanks so much!
-Surgeon-

[Dirk Diggler]

ALWAYS CHECK THE INCH LBS when you put the charger back together. My unit has 50inch lbs at the pulley. I was only getting 6psi with 46 inch lbs. increased it to 50 and got 9psi. The trick is to put just enough torque on the ball drive to get the impeller spinning properly. Not too much or you will put too much wear on the unit. must be perfect. I found that perfect was when I got 9psi adn the boost would not fall in the upper rpms. At 45 inch lbs, my boost would fall in the upper rpm's from 6 to 4.5 anytime I was above 5K rpm's. The additional 5 inch lbs solved my problem and i get a consistant 9psi out of my sn2000m. Hope that hleps...CRaig at paradisewheelsinc.com is where you can get parts.

[Surgeon]

Ok, after reading a bit more I've found that there are different size shims in addition to different numbers of them under the impeller so I guess I'll have to play around with them to find the proper combination. When you refer to the torque reading I assume this is done on an assembled unit. Is this measured by using the torque wrench to rotate the impeller's retaining bolt or the front pulley retaining nut???