Axle repaired and replaced. A quick run with the VDC OFF and guess what, wrong! Still low boost! This time I couldn't even get to 7 psi.

I went back and looked at the data log from the Z1 dyno run and sure enough, 8.4 psi which is at least in the ball park. What the heck is going on? Somewhere something has changed for the worse. After all that I have done the gremlins should be gone.

If my new drive belt comes in before the weekend I guess I will take the SC and unbolt it enough to rotate the volute so that I can get the 45 degree coupler on it the way that TopgunZ designed the kit. Once that is done I'm done working on this for a while. I have been working on this issue most of the summer and I just need a break before I do something I will regret later........

One other thing I noticed in the data, on the Z1 dyno run the boost built up very linear until red line where it dropped like a rock when the throttle closed like it should. With all of my runs the boost builds up to a point and then flattens out and then actually drops, VDC on or off. When the boost stops rising and flattens out it also becomes rather noisy jumping from one pressure to another changing around 1 to 2 psi during that time. Could this be caused by a bad BOV?

If it was just a leak it should just be a loss of pressure and pretty constant I would think. If the BOV starts leaking it could be fluttering and that could cause a rapid pressure fluctuation. Anybody seen this kind of problem?

I would hate to spend the $$ on a Tial (they are sexy looking) but at this point I don't give a damn about the money, I just want the boost to be where it should be.

Maybe I should fly TopgunZ down here for a weekend to help me solve this........

Which BOV are your using now? I do remember from older thread that the plastic Bosch bpv supplied with the Stillen kit not holding boost beyond the typical boost pressure from the carb legal setup. Guys increasing the boost usually stepped up to the Turbosmart dual port 25mm BOV. if you boost levels are at 8-9 psi the bosch should be fine though.

You still on stock cat? With my test pipes, my boost levels were below what I would get with stock cats. I should be seeing 11 to 12 psi but dynoed just below 10 psi.

Yes, I'm using the stock Bosch bov. It seems to be working because when I do back off of the throttle I can hear a bunch of air being let off but it could still be leaking.

Yes, again on the stock cats. I'm only looking for 9-10 pounds of boost and I should be there with my setup.

I broke down and ordered the Tial BOV from Jegs during lunch. I would rather have it and not need it than need it and not have it. I need to either give up or launch an all out attack on the problem. I don't give up easy........

I'm really looking forward to seeing what dyno numbers turn up with the other builds. It seems that with 8.4 psi I should have seen well over 400 whp or am I dreaming?

If you take a look at the stickied finished stillen supercharger builds thread, at 8psi for Stillen, the HP range from 390 to 445HP and they probably weren't done on the same type of dyno, correction factors or ambient temps. Results can vary.

I was expecting more from 9.75 psi but I only came up with about 436whp but I was tuned on 91 octane and depending on how "safe" the tune is, numbers can vary. Also, all cars are not built the same, some produce a little more power than others.

It's not like you're producing 350whp on 8.4psi. That would not be normal for a custom tune.

Did your tuner do a before supercharger dyno? Interested to see the before number for delta comparison as well. My before supercharger dyno was 288whp, so I gained about 148. Only mods I had before supercharger were Uprev tune and FI catback exhaust with stock cats.

The pulls that were done on the dyno were just so I knew where I'm currently at. The car is being remote tuned by Seb at SpecialtyZ. He just sent me an updated tune with more timing advance but I don't see much point in logging the data for him if the boost level isn't where it should be. I'm being tuned for 93 octane.

Yes, I agree that there are lots of variables with the build, dyno and tune. I have seen where other Stillen systems have pulled over 400 on the same dyno at Z1 but with the 8 psi setup. I have the 9 psi pulley and am getting 8.4 which is reasonable. The problem is that I can't reproduce the boost that they got on there dyno run. On the street I'm only seeing 7-ish.

How was the 8.4psi boost reading taken by Z1 compared to how you're seeing 7psi? Maybe two different methods? Maybe they tightened the belt system down just before the pull?

I have the AEM boost/AFR gauge with logging capability so the same measurement method was used. Since then I have added another idler pulley to the serpentine belt driving the SC jackshaft so if anything the later runs should have been higher because any belt slip should have been eliminated.

The only real difference between the two readings is that one was stationary on a dyno and the lower reading was done on the road. Now you know why this has been so difficult to troubleshoot.

Hopefully the Tial BOV will fix the problem. At the least it will sound awesome.haha

Tbatt. You need the pipe, clamp, 1.5psi spring, 50mm intake and then the 1.5" exhaust if you want to recirculate later to quiet the pissed off dragon down.

Thanks for the info. I'm ready to try just about anything to get this boost problem fixed. Anyone know a good witch doctor or exorcist?

I'm going to be using the TiAL QRJ BOV. It can be configured just like the Bosch so it should drop in pretty quick.

When I looked at the available springs I don't see a 1.5psi on their spring chart for any of their BOV. Where can you get a 1.5 or was that a typo?

http://www.tialsport.com/documents/w3_tial_qqr_sp.pdf

For SC applications they have a -2 or -3 spring.

Try verocious motorsports

Thanks! They had it, it's the pink one.

The TiAL is here and the pink 1.5 psi spring. It will go on the car this weekend and another leak test done.

This evening I'm taking the Z to our monthly car show, tomorrow night is club meeting, Friday night is family night and Saturday is some home projects. Sunday will be the day of the BOV install. I sure hope this fixes the boost issue.