I took her out for a brief shakedown last night. She runs great. My A/F gauge indicated highest level of stoich/lowest level of rich at all boost levels (I'm going to scan for accuracy later). What a difference the water injection makes. I'll get a data run this weekend.

The only disappointment was the I only saw 4 psi of boost at WOT. I am running 18-20 hg of vacuum cruising and at idle. I'm not quite as knowledgeable about this stuff but, if they guy who sold me the blower (his claimed rating at 10 psi) was only running say 12-14 hg of vacuum, would his net psi have been higher than mine? If this is the case, what is the actual psi rating that I'm running now, or is it simply vacuum + total psi output= final boost pressure? If not, I may upgrade to a newer SN series with a VR4 impellor upgrade since I built it to run at 10 psi (I thought about a Novi, but it doesn't look like one of those would bolt to the Paxton bracket that I have).

 

Indicated boost is the resistance of the engine to accepting the air added above atmospheric. Either your engine is more modified (easier ability to take the added air) than the previous owner's, one of the two gauges (either your's or the previous owner's) is inaccurate, or the previous owner's claim of 10 psi may not be compromised.

In any case, the added vacuum has little bearing on the boost indicated on your gauge.

Aaron

 

Shane,

I know a little about the SN's as I have one on my 89 right now.
If yours is NOT a VR4 then it will anly put out 650 CFM (According to Paradise Wheel). This is at MAX impeller speed (38,500).

Your not going to see anything close to 10# on a 350 unless you over rev it a bunch!!! and I can tell you from experience, it will not last if you do, and it will caost you 7 bills to have it fixed.

You should see 6-7 lbs if you have the pulley ratios correct.
If you are good with math, the blower ste-up ratio is 4.44:1.
You can figure your belt ratio X blower step-up X MAX Engine RPM you will run it to and figure out you Impeller RPM.

I run a stock 7" crank pulley and a 3.75" Blower drive.
I rev to 5000 MAX because the blower is turning 41,400 RPM at that.
I Saw 7 # with a 350, and 6 # with my current 383.

The smaller the blower pulley, the more boost you will make. BUT, you must also know what the MAX engine RPM can be so you dont smoke the Blower.

I tried puting on a bigger drive pulley (Slower Blower Speed).
I thought that i would be able to RPM the motor higher and make more power. I was so dissgusted with the overall reduction of power @ 3.5# of boost, that I quickly changed it back to what works.

If you have you ratios set-up like mine, you should see 7 # on yor 350.
If it still does not make that boost, you either have a warn out Head unit, or belt slipage.

Let me know if you are looking for another head unit, I am changing to a Vortech T trim, and my current SN was rebuilt about 1500 Miles ago.
I will let it go for a song, and it is a good unit with a $200 taper lock 3.75" pulley.

Good luck finding a VR4. They are rare, and going for $1000-$1400 on E-Bay. Paradise Wheel also DOES NOT recomend the VR4 for the street, and they have too much bearing preload, and short life.


Good luck to you and happy boosting

Chad

 

With the water injection you can probably trim your fuel back a bit .. You should be seeing in the neighborhood of 12-11.5 in your wb guage at WOT... idle and normal driving should show around 14.7 - 15.0 ish..

I agree with AKS, the idle vacuum can be various things from either vacuum leaks to even the duration of the cam at idle.... boost is boost... Are you running the same size pulleys , crank and supercharger that your friend was? Belt slip?

If the meter was displaying RICH that is in excess of I beleive 10-10.5 AFR as you pull back full ( if this is the case) it will come around keep an eye on your knock retard...

So it appears you have a lot to go to crispen things up...

Happy tuning.. there is a lot of expertise here...

mo

 

Blwn Bux....sent you a pm

 

Replied

 

I like your '96 Mo. Have you put it on a dyno ? Taken to the tracks ?
I love to have a blower or turbos in my '89-383.

 

Hey vettenut,

I'm getting close, hopefully in a few weeks. I have been really under the gun at work...

i will be posting soon once i have it finished... I'm hitting 10 pounds of boost and I'm finishing up the upper rpm's ( without going to JAIL) AFR it hits 100 before you know it...

The last engine pulled a 330 on a mustang dyno.. it was a stock 350 with a 7 rib kit and water injection. I didn't have it as closely tweeked as this one.

I'm hoping to hit very high 400's on a mustang dyno... there is a local guy with a dynojet, but I would like to have a good comparison...

regards,

mo