Finally done!!

**Nutzy19** · 08-17-2005, 08:58 AM

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...

**F=MA** · 08-17-2005, 10:44 AM

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

**F=MA** · 08-17-2005, 10:51 AM

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

**Dirk Diggler** · 08-17-2005, 10:54 AM

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!

***speedytang*** · 08-17-2005, 02:20 PM

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.

**Nutzy19** · 08-17-2005, 08:33 PM

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

**Red350DropTop** · 08-17-2005, 09:25 PM

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).

**Nutzy19** · 08-17-2005, 09:53 PM

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

**Dirk Diggler** · 08-17-2005, 11:31 PM

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.

***speedytang*** · 08-17-2005, 11:36 PM

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.