Rebuld question

[Dirk Diggler]

OK, successful rebuld,however, I used to get 8.5lbs of boost, maybe even 10 if I reved to 6000rpms. I now see the supercharger petering out at 7psi? Do I need to tighten the race assembly that puts pressure on the races/ball drive unit? I am guessing that it is not tight enough? I put 20ftlbs on the race doughnut assembly. Should I put 25 or more on this part?

[Dirk Diggler]

Well, I put 10 more ft/lbs of torque to the doughnut that holds the ball drive races in place and I am still only getting 7psi:( One thing I did do is I polished the back side of the supercharger where the impeller sits. maybe this is why I am getting less boost? Any ideas of why my boost is lower than it was orginally? I did add some trick shift hoping to see an increase, but no such luck:(

Also, I have a air fuel gauge and when I get into the upper rpm's (4800 and above) the air meter goes from yellow/green to red/ no lights :( (green is rich, yellow is stoich, red is lean and no lighs are really lean). As of now, I"m done for tonight. But I did change my fmu from a 6/1 to a 12/1 and plan on burning a chip to add fuel durring WOT. Any ideas on this part of my problem?

Just got back from changing the fmu and chip. The fuel problem is solved! But I am still only getting 7psi as compared to my orginal 8.5psi??? Any Ideas of how I can get my orginal boost level back?

[brian88lx]

You didnt do anything at all to the engine while your paxton was off at the machine shop did ya?

[Dirk Diggler]

Brian,

I totally forgot. It's been such a long process! I had been waiting 3 MONTHS for my headers..long LONG story. Anyway, during that time, I changed my cam, however, the cam change was not very significant. I had a ZZ4 cam and changed to a comp cam. LCA on both are 112. Duration on the old cam @ .050 was 208/221 and the new cam is 212/218. The old cam was a "reground cam" and it was off in duratoin on a few lobes. So I purchased a new cam. I don't think the new cam is the reason for the lack of boost, but it would explain the loss of boost :( . And the car does not seem to have any more or less power than before :o Thanks for the reply. Also did you see what I did to the valley for the dowel's on the case of my s/c?

[brian88lx]

Yes, I looked at those pictures quite a few times. I dont know how the heck that chipped off like that. I will definatly keep in mind to machine a couple extra just incase something like that happens. I may have a couple extra machined in when I buy the vr4 half next month while its all apart.

[brian88lx]

Wait, you put new headers on your car?

[Dirk Diggler]

My old headers cracked becasue i put header wrap on them:( I got the exact same headers, but coated inside and out. maybe the increased duration on the intake and the little decreas on the exhaust is what is causing the decreased boost? But 2.8lbs decrease over such a little change?

[brian88lx]

man. that is weird.

after you put the cam in it did you adjust the timing and such again?

[Dirk Diggler]

yea, the cam is 4 deg advanced as my old cam was. I am considering one of two things. One, keeping the sn2000 and upgrading to the vr4 OR saving more cash and then selling the sn 2000, and purchasing an ATI procharger. I love the stealth of the sn type blowers. Can harldy hear them:D love that! But the constant maintence of the ball drive units concerns me. I have heard a lot of bad things about them, however, I have had good luck with mine, 4 years, 15k miles, but I still worry about how long this rebuild is going to last. So for now, I'm saving my cash for the ati, but using my sn2000( and loving it). In the mean time, I'm enjoying having my sc on the car:D and plan to make a decision as of how this rebuild last me.

And the one draw back of the ATI, other than the cost, is the very noticable whine yea, it sounds cool, but you have to live with it every day That can get old, real old!

[speedytang]

Remember that changing a cam duration will change the boost you see but that does not mean your building less power. PSI numbers on a gauge really mean nothing without a dyno to see the changes and 1/4 mile times are not that much help because you can't make things equal on each run.

[Dirk Diggler]

Speedytang, I realize that a cam chance can increase/decrease the boost, however, my cam change was so small, i did not think it would matter. The only reason I changed cams was becase the cam i had was a regrind. I think the cam was off in duration in a few lobes. So i purchased a brand new cam to make sure it was a correct cam in all lobes. I spoke with craig at paradise and he said my impeller could need to be moved closer to the case of the supercharger.

[speedytang]

My impeller is so close that a piece of paper will not go between the impeller and case. You need to take a water marker and paint the case then keep moving the impeller close till you have paint on the impeller blade and make that last shim half as thick but remember that at 50k rpm the impeller could increase on the 'SN' style blade and that is why the VR4 impeller is made so different for a tighter clearance measurement.

[Dirk Diggler]

Well, I checked the clearance between the impeller and the back case. It was .025 so I took two of the 4 shims out, now it is .015 but have yet to check the boost level. Turns free, cranked up the engine and let it run for 10 min...everything seemed ok. Just have not had a chance to take her out for a test run:( I will later and keep you posted!

thanks for the help!

[Dirk Diggler]

I took it out and there was no change:(

[speedytang]

Without a comparsion like on a dyno or a few runs down a dragstrip the lower boost number could mean nothing if your power is the same. Cam, Headers, Intake design can all change a boost psi number but yet make no difference or like when I changed heads I lost 2psi but gained 48hp on the dyno. Just remember you changed other parts and so you might be chasing a boost ghost. That is why it is always said to make one change at a time to see if you decrease or increase power and that is why the magazines always show one change at a time to see one variable at a time.