HELP! 6 litre supercharged not holding boost

[xxbirchxx]

I'm a newby to tuning and trying to tune my mates car, it was going good then all of a sudden lost boost during a wot run at about 5200rpm.

Now it will only see boost up to about 3000rpm then bleeds down to normal map.

The engine still runs fine, its not pressurising the sump or blowing smoke or noisy.

Car is a 2008 holden commodore L98 (6 litre with 0821 heads) 6 speed manual, cam is 227/227 .598 .598 112lsa, harrop hh122 supercharger kit (third hand)

It has gilmer rear belt setup and 8pk front belt setup (the belt is too short and there is not much movement on the tensioner.)

I have replaced the manifold gaskets and tried holding the bypass valve closed but still does the same thing

In the log file "lost boost" you can see were the problem first started at 13:30:25

any ideas?

[SultanHassanMasTuning]

check the bypass valve or even any slack in the belts

[07MontRedcp]

I agree. I've had that problem and it was it was a leak on the control line at the bypass.

[GHuggins]

Even if the belt is tight - it can still slip if it's not wrapped around the crank and blower pulleys at least 75%... In the above log - your throttle is staying open - this doesn't mean your air filter hasn't sucked something up into it or collapsing - even possibly where the air box gets it's air? I would focus more on the mechanics than anything else as stated above - bypass valve which you said you held shut somehow - that should have eliminated it unless it's loose internally? Blower not seated on the heads correctly - shouldn't have built boost to begin with? If you have the ability - smoke check it - should show an external leak quickly - possibly rubber cork or nipple blew out somewhere? If it's not leaking - then has to be clogged internally or a bypass issue - that's if it's not a belt issue... Don't know if it's on a dyno or not - but easiest diagnostic is to have someone run it while you watch things - you might be surprised with what you see - such as a weak tensioner moving the wrong way "it should tighten down the belt with about an inch of movement in most instances"...