Finally done!!

Well... its installed.....
I have a few last ?'s
I installed my sn89 kit on my mustang ..
timing is still 12-14 degrees BTDC ( havent changed it yet )
Plug gap is still .050 stock heat range.....
If it runs good should I still retard the timing???
Should I re gap the plugs and or go a heat range colder and why???
Its not as powerful as I hoped...only making 4.5 psi at 5000 rpm..... It takes forever to climb to 4.5 psi.. I definitely feels faster but I want the most boost I can get out of this little sn89 .. any suggestions (other than a new blower )

If it works and doesn't detonate, then you don't need to retard the timing.

I use 10 degrees and .045 plug gaps but that's just what works for me. Colder plugs aren't needed and can foul at low load conditions.

It's a centrifugal blower, it needs rpm to work. 4.5 pounds sounds like it could use a little tweak in the pressure on the balls, it might be slipping a little.

Opening it up and inspecting it is really easy. Lots of experience with that here.

Don't worry about plug gap unit your at WOT and the car jerks like a rev limiter then close the gap on the plugs because your blowing out spark. The 'SN' rating is 5psi at 5500 rpm on a Mustang with stock Paxton pulleys, so your in the ball park. If you can hear your engine and its not detonating check your plugs for spots if not your good to go. If your plugs have spots on the ceramic then go one range colder on plugs.

how do I " tweak the pressure on the balls" ?? I think I have a line on an SN-93 to put in place of the SN 89...... What would I need then and how much more boost would I see? I think it would just bolt right up but would my FMU still be correct and would changing the fuel pump be immiediate or could I wait a few weeks till I have funds...

The 2 units are the same except for the outer case change. Same boost and would be the same impeller unless it has been changed but probably not.

ok heres the scoop.... Its and SN92 with a fresh rebuild on it ( still has Craigs tag on it ). My sn 89 has about 500 miles on it total in its life. I can upgrade to the sn 92 for nothing but I would have to swap pullies cause it was for a camaro and has a 3.25 pulley and I have a 4.25 pulley. What is the benefit of this and would you do it.....

Really same unit.
If your interested in selling one of the head units let me know.
My son has a new project and maybe I will get him a 'SN' for his birthday.
PM me if you want to sell.
Thanks

Quote:

---

Originally Posted by speedytang

My son has a new project and maybe I will get him a 'SN' for his birthday.
Thanks

---

:cool: :cool:

Quote:

---

Originally Posted by F=MA

It's a centrifugal blower, it needs rpm to work. 4.5 pounds sounds like it could use a little tweak in the pressure on the balls, it might be slipping a little.

---

How do I tweak the pressure.....

To do it properly, you have to tear the unit down and reshim the races. It's less hassle than doing a jet kit on a bike, say, since there's really only one variable and you're likely to get it right the first time.

Good luck,

F=MA

wow.... that was more vague than " tweak the pressure" ...lol

I think pavement pound has a web site that shows you how to reubild the sn series.

If you been reading the Forum for a while you will see that increasing the ball pressure to increase boost is not always a excellent option. The thing to remember is that impeller was designed for a certain boost range so spinning the blower harder may not give you the best boost. Example: You increase your boost from 6psi@180degrees intake temperature to 8psi@215 degrees intake temperature. Guess you got your 8psi but guess what, you just made your car perform like it has 4psi because of the density of the air and you also took a year of your superchargers life. Your better off putting a Water/Meth injection unit and run full timing and gain real horsepower without all the negatives of spinning a supercharger over its impeller boost design.

you could get a VR4 upgrade, I know who has the last one:D

Dirk Diggler has your only option other than going to a different supercharger if you want more boost. The VR4 pushes twice the CFM of air per psi of boost.

The Sn89 on my car now only pushes 1 pound of boost at 3500 and at 4500 its like 3 but peaks at 5800 at 4.5 . I dont want more boost I want earlier boost. Not like a roots I know.. but it should make some boost sooner.... 1 psi is horrible. Ive checked everything to see if Im losing boost and its all good. Im ready to sell this thing...

PSI isn't a measure of anything but inlet restriction. How's it running? Does it not feel majorly stronger all through the rev range, particularly up high? Stop fixating on the boost gauge and find out what power it's making. Take it to a drag strip on street legal night or do a dyno run. Tuned half-decently, I'd bet money your stocker is hitting around 300 horse, which ain't bad for a bolt on upgrade.

I stil think you might get a little more sooner by tightening up the ball drive a little.
F=MA

PSI isn't a measure of anything but inlet restriction. How's it running? Does it not feel majorly stronger all through the rev range, particularly up high? Stop fixating on the boost gauge and find out what power it's making. Take it to a drag strip on street legal night or do a dyno run. Tuned half-decently, I'd bet money your stocker is hitting around 300 horse, which ain't bad for a bolt on, used part upgrade.

I still think you might get a little more sooner by tightening up the ball drive a little. If your car has stock heads/intakes/cam/headers, 4.5 can be hit by around 5k.

F=MA

If it's making 1 psi of boost @ 3500, then 4.5 @ 5800, it's working. I wonder if you have a vacume leak or something. Maybe, MAYBE your loosing boost becasue the boost is escaping via a tiny vacume leak? Take some carb cleaner and check for leaks, or get some soapy water in a spray bottle, blip the throttle while squrting it on mating surfaces and look for bubbles. Only 1 psi @ 3500 does not seem right, but if you have the old impeller, it could be par for that setup, also, your cam has a lot to do with the boost levels. Anyone here running the SN89? Ask them what boost they are running?

The old impeller desighn only yeilds 6 psi. Now, the VR4 builds boost at a much lower rpm, even lower than most blowers, with the exception of the roots style. Are you getting a lot more power from the unit? Also, if you have a lap top and diagnostic software, really pay attention to the knock sensor. You can run a more agressive initial timming and pull timing out of you can burn you own chip and get a ton more power in this manner. I set my inital timing @ 8deg advanced, and pull timming out in the upper rpm's. I think @ WOT 5500rpms, I've backed my timing off to about 21deg total...but that's on a supercharged car, not NA. I think the program for the stangs are ones such as the EEC tuner. Get a cheap laptop P233, make a cable and software, good to go!

I myself would also move the port your using for Vacuum/Boost. Something is wrong if those are the numbers and it is probably not the Blower.

its plugged in at the vacuum tree ..... 91 mustang GT

Have you checked the clearance between the impeller and the scroll cover? Excessive clearance is wasted boost there. You can shim behind the impeller to bring it closer to the cover. I put my VR-4 at about .005" from the cover. John Myer, a guy who rebuilds SN-60s for Studebakers, runs his as close as .002". I had my SN-60 set a .002 and the impeller kissed the scroll cover in one spot. The SN-60 impeller is magnesium as I remember, so I don't know if that affects how close you can set the impeller (growth of the metal from heat).

Could it be my lack of fuel pump upgrade causing this??

no, if it were your fuel pump, you woudl feel it die at a certain rpm. When I had my stock fuel pump in, @ 3500rpms the car would just loose power, still produced boost. It would fall flat on it's face @ 3500.

Your problem is boost which takes rotation. Fuel pump is working I don't know if your lean but your seeing 4+psi at 5800 rpm. How about your belt is slipping when you floor the car causing it to slip then it catches up at higher rpms. I checked tonight driving my car and datalogged a couple of 0-60mph runs. I see 4.8 psi @ 3200 rpm leaving the line at 1800rpm average. I also took a ride with my son in his car that we just installed a 'SN89' in his car and watching the boost gauge because we don't have a system to datalog but he has a boost peak gauge and when he said 3500 rpm on his accurate tach I seen 3.5-4psi it was moving fast and at 4800rpm he was seeing 5.5psi. Now on his installation it is a direct drive the blower to the back of the camshaft. NO BELT. This system when completed I will take pictures it is the best setup we have designed yet.

wow Dirk we are typing at the same time

Haha

Id like to see those pics.... I have to move the inlet tube into the fenderwell then Im gonna chase down this BOOST demon...

Me to !