Boost problems

bmo37 · Nov 17, 2004

i've been fighting this problem for awhile now, I basically built and engine from the ground up by myself, and the last piece of the puzzle was the supercharger. Now for the life of me I can't build any boost, at idle it reads 0 psi, just all vacuum (don't know vacuum reading cause only have a boost guage)

Only time I can get my boost gauge to read anything is when I rev the car to 5k plus rpm's and only than does the gauge spike to 7psi and drop off instantly again. I'm basically out of ideas i checked all vaccum lines, car idle great no leaks, I have a basic tweacer program in it for the injectors, maf size, startup fuel table, and cid.

Only thing i can think of is that maybe its the cam and the overlap it has isn't good for a boosted car. My current cam is a trickflow stage 1 cam. Don't know any ideas would be great, thanks in advance.

Daggar · Nov 17, 2004

What's it feel like when you drive it? You getting boost then? What are you using for a bypass valve? Is it stuck wide open except for the most extreme low vac setting? Disconnect the bypass valve and wire the thing shut. Rev the car up a little and see if your boost guage rises. If it does then it's your bypass valve (or BOV, whichever you use). If you can feel that you're getting boost when you drive then it's your guage or the vac lines going to it. If you close the bypass valve and you can't feel boost in the seat of your pants then something probably seriously wrong with the blower. Even a slipping belt would provide you with some boost.

lit_mike_2001 · Nov 17, 2004

i dont know **** about superchargers but check all of your plumbing from ur air filter to the intake, it sounds like a hose is collapsing or leaking

bmo37 · Nov 17, 2004

Daggar said:
What's it feel like when you drive it? You getting boost then? What are you using for a bypass valve? Is it stuck wide open except for the most extreme low vac setting? Disconnect the bypass valve and wire the thing shut. Rev the car up a little and see if your boost guage rises. If it does then it's your bypass valve (or BOV, whichever you use). If you can feel that you're getting boost when you drive then it's your guage or the vac lines going to it. If you close the bypass valve and you can't feel boost in the seat of your pants then something probably seriously wrong with the blower. Even a slipping belt would provide you with some boost.

Car feels nasty when driven, but I can't tell is its at its full potential since I just did a complete engine build. Don't know if the power is the engine by itself or engine and sc. Not getting any boost when driving. I'm using a bosh bypass valve. I actually removed it to test the boost and it made no difference. I tested the gauge and line seperate from the car and they work. I actually removed the t-body to valve cover plug and it shoots air out of there when at idle and when reving.

The thing thats stumping me is I'm not getting a constant boost at all, I mean i know it will flucuate with rpm but I should see some boost at idle. I've been replacing all the vacuum lines but not help there. What it seems like is i never build the boost up untill i run the car really hard and long, for instance if i unplug a vacuum line I never feel boost pushing out when at idle or reving rather just vacuum. I don't know I'm just really stumped.

Daggar · Nov 17, 2004

Assuming you're still running the SC trim you have listed in your sig... This may sound crazy but I think you've run out of blower. It's not keeping up with your combo. It sounds to me like your new 347 is capable of injesting more air volume than your blower is capable of putting out. Especially if what you say about running it long and hard is accurate. It would explain why you're getting nothing on your boost guage. The motor is spinningup faster than the blower is capable of keeping up. Once the motor levels off and the blower peaks, you see boost. It would also explain why you're still feeling vac from tubes when you disconnect and rev the engine. I'm assuming allot here. For starters, I'm assuming that your vac guage is taking it's reading from the intake plenum. I don't think that your cam overlap is causing your problem. If anything the overlap would reduce your vac pressures, not create more. Sure sounds to me like your cubes and combo have overcome the little SC Trim.

How about you others? What say you?

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