Boost trouble

[F=MA]

That sounds fine. Boost #s are a function of how restrictive you intake tract is, not how much air your blower is pushing. Cylinder heads and cam, lower boost numbers but WAY more power over restrictive stock crap.

Frankly, I wouldn't overspeed this blower. Technically, it'll handle max 40K but, it won't live long at those speeds and pressures, unless you run an oil cooler. Atop that, you're pushing the stock head unit out of its efficiency range, thus heating the charge more as well. It's a simple, well-engineered street blower. If you want to push big numbers, you need a VR4 or a complete changeover to SN2000 or similar.

The pulley you have was designed to go with a 7" crank pulley. That will give 6-7 psi and pretty much max out a stock SN. The 3.75 inch blower pulley alone will way overspeed the unit at 6000. 42000+ rpm.

Here's the equation;

Crank diameter/blower diameter X max rpm X blower ratio.

The stock SN blower ratio is 4.44:1.

F=MA

[daviszx3]

ok thanks alot i really appreciate everyones help i would be lost without it, so i've heard you can change the crank pulley n get more boost without overspeeding the unit is this true? also how much could i expect from the upgraded impeller?
yesterday i was on the way to work and the charger threw the belt and then it threw the serpentine belt but everything looks inline anyone else ever expeirenced this problem i think i might have to short of a belt cause its really close to where the fan mounts to the water pump in i have to take the tensioner off to get the belt on you think that could cause it? thanks again

[F=MA]

I haven't heard too good reports about the "upgraded" impeller. The VR4 upgrade is the only meaningful change one can make to the old girl, imho.

I have never had one chuck a belt either. The SN tensioner assembly is a little cheesy in my view so, it is possible but, it hasn't happened to me in three years of racing this blower at the track. I think I'm using a belt I snatched in the junkyard off a 2.3 Ford, IIRC so, it wasn't even new when I got it. :happy:

Your theory on enlarging the crank pulley for more boost is sound for all blowers, not just the SN. In fact, that's the best way to do it. People go the blower pulley change route because it's cheap but, there's a very real possibility of belt slip, due to the tight radius, limited belt wrap and higher flow demands.

F=MA

[daviszx3]

would you happen to no the p# of the belt you are using

[F=MA]

It's a Goodyear Gatorback 4060495. The other number on it is 6PK1255. One of those should work.

F=MA

[JPJP]

I have good things to say about the high output impeller. CUNDN racing claims 2-3 psi increase.
http://www.cundnracing.com/servlet/t...charger/Detail

We upgraded my dad's '85 Corvette (back in the 80's) and felt huge gains according to the old "seat of the pants" dyno. Back then they (Paxton) claimed a 1-2 PSI increase in boost.

I plan to go this route when I rebuild my present unit.

BTW I have the 3.75 dia. pulley on my Mustang. Getting the right belt length and keeping it tight was a pain initially. I have an '86 so I keep the rpm's down anyway because of the nature of this year's power curve...and of course overspeeding the sn unit.

[daviszx3]

well everything seems to be workin great i got my oil cooler on and gonna get a shorter belt in try out my smaller pulley soon do you guys see any increase with the power pipe?

[daviszx3]

another question my car is a 90 mustang notchback and last time i went to track i went 14.40 on street tires mods are exhaust and 373 gears and now since im gettin about 5psi and hopefully gonna have some drag radials what kinda times u think i could expect

[speedytang]

Well your really dealing with tires not getting grip and a Supercharger is not going to help at all. My Stang with 3.08 gears and 265-50x15 stock rims and only a Cobra intake ran 13.70 @ 103mph. Same combination with a VR4 running only 6psi I went 12.68 @ 108 mph. Figure that math and you will see without me posting the 60' that the Supercharger took care of my lack of traction. I think with NO Supercharger my 60' was like 1.97 and with the Supercharger it was 2.29. Now with Drag Radials and 3.73 gears installed and the VR4 at 8psi by 2600 rpm I ran 11.67 and 123mph and a 1.7? 60'. I have only seen a power pipe help when your over 8psi on a 'SN'.
At 5psi and everything else equal you should drop 1 sec in the 1/4th and you will see the biggest improvement at the 1/8th.

[JPJP]

Oh, about the supercharger belt length you were asking previously. I am using a 48.5" long belt with the 3.75 S/C pulley and 6" crank pulley. I originally used a 49" belt but it stretched and I ran out of adjustment. At least that's what worked for me. May give you a reference point anyway.

[daviszx3]

ok thanks alot i'll see what happens and post up times when i go

[F=MA]

88 speed density Mustang, stock SN, stock heads with 1.7 rollers, off road H, Flows, ported lower intake, drag radials, 3.55 gears, 3260 lb race weight. 12.8 @ 108.

F=MA

[F=MA]

Well, seeing as it looks like we're losing SCH shortly, if anybody wants my personal email for help with the SN, here's one that'll last:

kchristensen@sd43.bc.ca

Anyone who wants to add theirs to our little "mailing list", shoot me the email at the above addy.

F=MA (Ken)

[daviszx3]

ok thanks alot my email daviszx3@yahoo.com

[daviszx3]

i checked the boost tonight with a guage i just bought in im only seein about 3.3 psi at 5500 do i need to tighten the ball presure? it still feels like its pullin good, i got the guage hooked in at the back of the plenum or you can email me daviszx3@yahoo.com