FAQ: Boost Bypass Valve/Boost Control Solenoid Questions (No Boost)

You say its a rebuilt SC. Who did the rebuild and did they strip the rotor coating?
The next thing is who ported the blower and whats the outlet look like?

Steve, first thing you want to be sure of - is AutoTap reading boost or MAP? Are units set to PSI or In-Hg? Reason I ask is because 25 In-Hg just happens to be the same as 12.28 PSI. I didn't think AutoTap will read boost, but maybe you have a different version than I do.

If your units are set to kPA, and you are reading MAP, then approx baro pressure would be 101 kPA + 25 kPA = 126 kPA, or 18.27 PSI boost. That seems quite high, so I doubt you are reading in kPA.

its reading the MAP, but does the conversion to PSI it says raw value 33 coverts it to 4.78 psi. max with the old SC was 22.64 with 60- 80 intake temps with the new S/c machined outlet and ported and polished intake 3.4 pulley 25.08 PSI at intake temps from 72 - 90 (min / max) temp 1.4 degrees of knock max MAF was readin 10406 Hz coolant temp average 181 max 190 stil need to get my fans re programmed for the T stat.

Intake temps aren't going to make a big difference unless you are comparing winter to summer.

Just machining the blower and TB shouldnt yield that much gain in boost, IMO. Check your MAF numbers (not MAFF) to know how much increase in air flow you have. 1.4 KR is not bad. What did you see before?

before was 0 KR with 7.9 LBS boost stock with the S/c ported inlet and outlet and 3.4 pulley making 10.4 LBS with 1.4 KR

where was the vac leak?

went to the 98+ SC from a 97. its missing the vac line to the lowwer intake on the front side. its a totally different set up so i ended up drilling a hole in the stock elbow and got the factory vac line from the junkyard that raps around and stuck it in with some silicone. Seems to work fine and nothing acting weird like before... althought i still hear some weird noise from the air box sounds like a door keeps moving. but the air still works fine. Now i have a leak at the elbow from the lowwer intake.

hhmm

2000ws6transam wrote:

before was 0 KR with 7.9 LBS boost stock with the S/c ported inlet and outlet and 3.4 pulley making 10.4 LBS with 1.4 KR

You are running a 3.4 pulley with no airflow mods besides the three angle valve job? 1.4 is not bad, and really not enough to worry about. Go to a 3.5 and that will go away. I couldn't get my 3.4 pulley to run KR free until I added 1.9 rockers.

yeah, i decided to wait and do the heads and lowwer intake because i wanted to get a tune after its all done. no mods besides the S/c 104's and K$N . i would like to get headers/ exaust full 3" that is simmilar to stock sound levels. and then go with a N* set up for the intake side.

Will be difficult to do full 3" exhaust at stock sound level, nor do you really need to change anything downstream the headers until you are making 400+HP.

I agree with deekster that 1.4º KR at WOT is more than acceptable.

So i noticed recently my car was running a little sluggish, but with work and school, i havent had much time to investigate, but tonight i skipped the gym and went to play on the SS Buick instead... took out my trust torque app, and right off the bat i saw the problem...
Background: Bone stock car with a homemade cai, 180 stat, stock everything else, was about 60 degrees out, IAT's were 70-75 during the runs... did 3 runs all showing the same results vaccuum and timing looked normal, .7 max degrees of knock on the initial hit on one run, none on the others, i ran the car to the limiter in 2nd gear (6000) all 3 times and looked at the maxes, max boost: 3.8, 3.9, 4.2... max cfm all in the high 1400's.... on my timeslips from the track i always right down my maxes and they usually show max boost of 8-9psi with a max cfm well in to the 1900's sometimes eclipsing the 2k barrier... now this is my first supercharger car and i honestly dont know much about boost leaks and all that jazz... but any ideas on what would cause this?

Sounds like the BBV is disconnected. Check all your vacuum lines. The T fitting under the SC snout can become brittle and break and then there is no vacuum to actuate the BBV. (Boost Bypass Valve)

Deek, you were right on the spot, good man... the T was just kind of hanging on there, and when i took it off the hard line going from the T to the other T on the front valve cover snapped... so i went to all the auto parts store and none have seen anything like that... so im assuming they're special order from GM?... and thats if they even still make them, is there a better fix?

LT1Squirrel wrote:

so im assuming they're special order from GM?... and thats if they even still make them, is there a better fix?

They are pretty much made of unobtanium, sorry to say. I think you can try to order a "vacuum harness". I seem to recall that somebody sells that tee separately now but I can't remember who. Cobbling together with universal tees really sucks and looks like shit.

Also try Morad's...

Yeah, right now its pretty hacked together, it works... but it just looks plain fugly haha

No worries, go to a dealer and order the vacuum harness for the 3800 engine. It will take a while to find because I think the P/N has been superseded more than once. I did this around a year ago, I might have posted the P/N but I don't remember. Point is just go buy the harness.

I got the T from rockauto, I think. May have been GMpartscounter.com.

MFFDVR wrote:

I got the T from rockauto, I think. May have been GMpartscounter.com.

Any chance you have a part number?

So i constructed some lines, and its actually pulling more vacuum than it ever has at all RPM's lol... but now i think the BBV may be the culprit for the low boost, is there a way to diagnose or bypass it to see if that is causing the problem?

Pull a vacuum on it with a vacuum pump and see if it holds. You should see it actuating when you quickly snap the throttle to rev the engine.

deekster_caddy wrote:

MFFDVR wrote:

I got the T from rockauto, I think. May have been GMpartscounter.com.

Any chance you have a part number?

I'll try to find the shipping reciept. It's been a while, but I do keep that stuff, somewhere.

deekster_caddy wrote:

Pull a vacuum on it with a vacuum pump and see if it holds. You should see it actuating when you quickly snap the throttle to rev the engine.

i would run to my bro's shop and grab it, but all the boys are in OCMD for the cruise this weekend... any other way to check it? haha

so i did exactly what post 16 in this thread: http://www.grandprixforums.net/booooost-68178.html
and full boost has returned, but knock is now erratic, so the control valve is the culprit.... now the problem is finding the most up to date part number for it, because i dont like the way it looks under the hood

Knock is erratic because you have full boost all the time. I wouldn't run like that besides the test.

Morad's probably has plenty of BBVs.