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Old 05-07-2016, 03:19 PM   #1
fullcircle
 
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Drives: 2009 Pontiac G8 GXP
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loosing boost above 3500 rpm

Just got back from the dyno shop for the first run with the 2300 Maggie. Ran into a odd issue the car holds 10 psi boost until around 3500 rpm then drops off to 6 psi by 6000 rpm. Running a cog drive in rear 3.8 front pulley with super damper didnt see any signs of belt slip or the bypass opening? Was going to ask Magnuson on Monday just thought I would ask here as well.
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Old 05-07-2016, 03:47 PM   #2
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are you sure that the bypass is not opening?
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Old 05-07-2016, 04:42 PM   #3
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Take it to a better shop
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Old 05-08-2016, 10:47 AM   #4
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if you find the issue would like to know. having similar issue with mine. bypass valve has been replaced.
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Old 05-08-2016, 02:43 PM   #5
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what cam? what other mods do you have?
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Old 05-08-2016, 02:50 PM   #6
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Belt slip. Once you start making boost, the belt stretches. If the belt isn't the shortest one you can wrestle on there, the tensioner will run out of travel and lose the ability to keep the belt tight.
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Old 05-08-2016, 06:42 PM   #7
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I'm running the supplied belt with the 3.8 pulley and overdrive cogs.
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ported throttle body
sp headers with cats
loud mouth axle back no mufflers
tuned by steve williams 6l80etuning.com
bmr split springs
cam motion custom camshaft
btr 660 spring kit
maggie 2300
id850 injectors
livernois fuel pump
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Old 05-08-2016, 08:53 PM   #8
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I found the smallest belt I could barly get on and its tension is super tight. Slid the adjuster pulley as close as possible to the tensioner
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Old 05-08-2016, 11:28 PM   #9
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Could be belt slip, but a 3.8" pulley doesn't seem that small. How about calibration, have you logged throttle position? Torque management isn't closing the throttle is it? Just a thought.
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Old 05-09-2016, 12:20 AM   #10
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No pretty sure torque management is turned off even tired it without the air cleaner it ran worse.
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Old 05-09-2016, 05:41 PM   #11
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Well I have full boost!!! When I called magnuson and asked how to set the vacuum actuator after I removed it to install injectors they said to push it down half way. So I just pushed it down all the way and reset the set screw and now I have full boost. Thinking that the mid point might be a preset setting to keep it at its stock 6 psi boost.
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Old 05-09-2016, 05:59 PM   #12
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Great info! Glad you got it figured out
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ported throttle body
sp headers with cats
loud mouth axle back no mufflers
tuned by steve williams 6l80etuning.com
bmr split springs
cam motion custom camshaft
btr 660 spring kit
maggie 2300
id850 injectors
livernois fuel pump
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