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High RPM power fall off turbo 4.8 - Help!

Old 10-20-2017, 01:16 PM
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Is the log wrong or the MAP scaled wrong or am I missing something? The scan showed a max of 8psi. Or was that a low boost pull?

Just curious is all, though after reading the rest of this I tend to agree it needs more turbo and less rpm if running just LS6 springs.
Old 10-20-2017, 01:26 PM
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Originally Posted by FFDP
Is the log wrong or the MAP scaled wrong or am I missing something? The scan showed a max of 8psi. Or was that a low boost pull?

Just curious is all, though after reading the rest of this I tend to agree it needs more turbo and less rpm if running just LS6 springs.
One pressure sensor parameter is screwy on this log, the 2 bar sensor is the correct one.

Do you know of people having issues with ls6 springs and boost?
Old 10-20-2017, 01:43 PM
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At 13-15lbs of boost, you just might be pushing past the valve springs. Before upgrading the turbo, I'd definitely swap something with better seat pressure in there. The PAC1218 springs seem to be the go-to for budget builds.
Old 10-20-2017, 02:12 PM
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Originally Posted by BudRacing
At 13-15lbs of boost, you just might be pushing past the valve springs. Before upgrading the turbo, I'd definitely swap something with better seat pressure in there. The PAC1218 springs seem to be the go-to for budget builds.
So are you implying on the compression stroke the manifold pressure is opening the intake valves and bleeding cylinder pressure into the manifold?
Old 10-20-2017, 02:30 PM
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I'm implying that the pressurized intake air is pushing its way past the valves (into cylinders) that would otherwise be closed.
Old 10-20-2017, 03:13 PM
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I have a gauge for that
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If anything you would have more of an issue on the exhaust side than intake side.
Old 10-20-2017, 08:41 PM
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Originally Posted by Atomic
If anything you would have more of an issue on the exhaust side than intake side.
so with a 3 inch dump this issue has almost gone away, I think I have just pushed the problem further up.

Thanks for the help guys!

Also Atomic I'm starting a thread in the fuel system page that I would love to hear your input on. its sensor related.
Old 10-21-2017, 10:28 AM
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Valve springs get blamed far more often than they should. This is one of those times.

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