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Boost controller/boost build up question

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Old Sep 4, 2015 | 03:45 PM
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Default Boost controller/boost build up question

I have a 98 Trans am, 6 speed, 243 ported heads, blower cam, and on3 76mm turbo kit. I have the innovate scg1 boost/wideband and boost controller gauge, but have been noticing that the boost wasn't very steady. Sometimes peak would be 7-8 and sometimes it would hit 12 psi. Has 7 psi wastegate spring and the controller is set to cut it at 10 psi. I decided to put a hallman pro manual boost controller on it. I decide to try out the data logging that the gauge has and noticed that my boost wasn't very smooth, it fluctuated. Still kinda new to this, thought it would build up to what the controller is set at and be nice and steady. I'll try to post a snap shot of the log. Checked for boost leaks and didn't find anything.

In the picture the red line is boost and the black like is rpm, the drop is from 2-3 shift
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Old Sep 4, 2015 | 03:57 PM
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Originally Posted by dieselman88
I have a 98 Trans am, 6 speed, 243 ported heads, blower cam, and on3 76mm turbo kit. I have the innovate scg1 boost/wideband and boost controller gauge, but have been noticing that the boost wasn't very steady. Sometimes peak would be 7-8 and sometimes it would hit 12 psi. Has 7 psi wastegate spring and the controller is set to cut it at 10 psi. I decided to put a hallman pro manual boost controller on it. I decide to try out the data logging that the gauge has and noticed that my boost wasn't very smooth, it fluctuated. Still kinda new to this, thought it would build up to what the controller is set at and be nice and steady. I'll try to post a snap shot of the log. Checked for boost leaks and didn't find anything.

In the picture the red line is boost and the black like is rpm, the drop is from 2-3 shift
What's the specs on the cam? Blower cams and turbos don't usually go well together if there is any overlap.
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Old Sep 4, 2015 | 06:43 PM
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Cam specs are
231/235 617/621 115 LSA
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Old Sep 4, 2015 | 07:25 PM
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Yeah... That's a pretty big cam for the On3 76mm. Im sure the turbine is having trouble with that one. Any idea how much overlap @.050?
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Old Sep 4, 2015 | 07:46 PM
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im not real sure, the cam was in the car when I bought it. its a custom grind. so would I have to swap the cam, or get a different turbo to match it better?
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Old Sep 5, 2015 | 07:06 AM
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would having too big of a cam for the turbo cause the uneven boost psi? I was thinking maybe a faulty wastegate
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Old Sep 5, 2015 | 07:53 AM
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Originally Posted by JoeNova
Yeah... That's a pretty big cam for the On3 76mm. Im sure the turbine is having trouble with that one. Any idea how much overlap @.050?
If I'm doing the math correctly it looks like 3* overlap.
Maybe someone can verify.
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