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Early rev limiter with 24psi

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We are tuning a turbo 6ltr LS with a 6L80 tuned with the factory ECU

Car runs beautifully from 14psi with 800hp all the way to 22 psi @ 940hp. The tune is awesome, car starts cold and hot idles nice and has huge power, great afrs

Engine has been built specifically to run big boost with a relatively small cam in which made more power than the larger cam previously fitted.

We have a stand alone boost controller (GFB). We attempted 24psi and am now getting an engine cut out signal toward the top of the power curve before (about 5800rpm) it even gets to peak RPM, like its hitting the limiter, limiter set at 7000rpm

We thought perhaps it may be a torque management cut out from the transmission but we have been through all the torque management settings and set all to either max out and or min end of the scale with zero difference. Anyone experienced this?


Nice work, sounds like a great combination! Can you provide the current calibration and a log file of this cut occurring? It will be easier to diagnose with some data.

It isn't something as simple as running out of range on the MAP sensor and having the ECU go into a protection mode?


My thoughts too but its a 3bar MAP so it shouldnt run out of range @24psi


Will get a log of this

Looks like the boost pressure is shutting the throttle plate!!!!!!

Is it calibrated for the 3bar sensor?

What about part or close to full throttle, or applying full throttle from, say 50% when over 6k rpm?

Is it a hard cut, does it pick up again when it loses boost from the cut?

What about fuel pressure, spark plug gaps?

Boost pressure, alone won't be closing the throttle, it must be something triggering it - I assume it's DBW, from the comment? [edit] Thanks for the correction there, Stephen

I have seen boost pressure blowing a throttle plate closed, typically it happens when there is a tight bend just before the throttle plate so the greater mass of air is on the outside of the curve, and the throttle plate opening direction is into this mass flow. What happens is that the plate no longer has a balanced airflow across the whole plate and the leverage provided is enough to push the plate closed against the DBW motor. This is worse on "upsized" throttle where the bore has been enlarged and a larger plate installed with no matching improvement in the drive system. The plate has a greater leverage and the original motor can no longer hold against it.

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