Turbo boost cut off?

[Philip Parker]

I’m sure someone here can explain this:

So in the dash I have a green turbo light. I assume this is from the turbo boost sensor indicating positive plenum pressure.

If I am too aggressive on the gas and ring the engine out, right around 4k rpm with the pedal to the floor, the light comes on and I get a buzzer from the dash and the engine cuts out like a rev limiter but more violent.

Is this normal?

Phil

[Daniel Roy]

Yes it is normal, you hit the boost cut off. You must have at least a freer exhaust and or a boost controller for your boost to go higher than stock. Or your waste gate is jammed preventing boost control. If you have the mods to support the added boost with added fuel (chipped ECU or HKS F-CON for example) you can unplug the sensor. You won’t lose the green turbo light as this light is controlled by the ECU who determines that the engine is in boost by the other sensors, the ECU has no boost sensor. The boost cut off sensor is only a safety against overboost, it is a switch and not a variable output sensor.

Dan

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[Joel Sass]

I can add a bit to this by saying that if you have enough flow in the intake and exhaust, the boost will creep up to 1 bar without a boost controller even when the waste gate is fully opened. For my vehicle, it would hit 14 PSI around 5500 RPM. Highly recommend that you purchase a boost gauge to monitor manifold pressure. 

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[Philip Parker]

Gotcha. The only mod is a custome down pipe and 2.5” exhaust all the way back. 

I really do think the noise that I’m hearing is the turbo back spooling when I come off of the gas. Is there a plug and play waste gate that anyone can recommend just so I can remove that from the equation? 

Phil

On Jan 25, 2023, at 3:03 AM, Joel Sass <sass...@gmail.com> wrote:



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[Bob Martin]

The downpipe and exhaust are enough to cause boost creep issues. The stock turbo has a very small exhaust bypass port. With low exhaust system back pressure, the exhaust gases find it easier to go through the turbine wheel than the bypass port when the wastegate is open and this causes the turbo to keep speeding up and up goes your boost pressure. The solution is to drill out and blend the bypass port on the turbo so that the exhaust gases can get out that way easier.

AS for the wastegate, do you mean blow off valve (aka recirculating valve)? The stock ones often go bad. The standard replacement is a Bosch blow off valve (Google bosch blow off valve and it will be the first item to come up). You don't want the non-recirculating type valve as that wastes fuel.

Bob

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[Philip Parker]

I see. 

Yes! Blow off valve (waste gates are exhaust side?) - I see the Bosch one with the Ports at a 90 degree angle…is that the correct one? 

Phil 

On Jan 25, 2023, at 6:56 AM, Bob Martin <wz4...@gmail.com> wrote:



[Philip Parker]

Follow up question: I’m assuming these valve have flow/pressure specs, and I’m curious if there is a way to spec a valve to keep boost in control because of the exhaust mods. 

Phil

On Jan 25, 2023, at 7:09 AM, Philip Parker <philiptho...@gmail.com> wrote:



[Bob Martin]

The BOV has nothing to do with boost pressure. You need to port the wastegate.

[Philip Parker]

Roger that. 

On Jan 25, 2023, at 7:23 AM, Bob Martin <wz4...@gmail.com> wrote:



[Joel Sass]

A Wastegate is used to mitigate the speed of the turbocharger by diverting exhaust gas away from the turbine of the vehicle. The integrated wastegate in IHI turbos is a hole with a flapper that opens up between the compressor and turbine, and is notoriously inefficient. The same design was used with the RX-7. People would modify the hole by widening it up, but the best way to go is using an external wastegate. A blow-off or recirculation valve is used to release pressure from the compressor side of the intake system. A blow-off valve vents the pressure to atmosphere, while a recirculation valve vents the pressure to the intake somewhere before the turbo compressor, but after the mass airflow meter. For the record, a blow-off valve in the GTX will lead to stalling after coming off high boost to idle because of the lack of metering. I recommend you look for a recirculation valve solution if you're going aftermarket.