ciprianrx8

Here is a suggestion for boosted renesis engines that run a standalone or can run something similar:
Use the air pump valve solenoid as a boost cut off/overboost protection. It is already there, it needs some wiring, but it works wonders.
To do this, I've tied the output of the solenoid towards the blow off, and the normally open port had vacuum or boost applied to it from the nipple after the throttle body. The normally closed port is plugged into the vacuum chamber - the same as it was made by Mazda.

When the solenoid is off, the blow off works as usual and the solenoid does nothing - it keeps a direct path from the blow off to the vacuum or boost that can be found after the throttle body.
When the solenoid is on, however, the vacuum from the vacuum chamber(of those 3 solenoids) is directed towards the blow off. This should cause it to open, regardless of engine speed, load, or boost pressure if any. With the blow off open(and it dumping the air back towards the turbo intake) the engine will never build any boost at all.

The catch here is getting a signal to that solenoid... I've got my own microcontroller to do that, but a standalone ECU or even a simple arduino and a relay/transistor will do this.
You can even wire in a simple boost switch to toggle the relay when boost > threshold.

I've tried it and can say it works wonders. I run a 15psi pressure sensor and 4x open drain transistors tied to a microcontroller(teensy 4.0) that also does electronic boost control. If the boost pressure exceeds the target by 20%, this BOV solenoid is energised and thus all boost is killed on the spot for 10 more seconds. During these 10 seconds, the engine is free to run as NA. Of course, there are multiple reasons why it will or not trigger this protection, there is more to it.

This ideea came to me after Brett telling me how he uses his VDI solenoid as a boost cut-off, but only RPM dependant. That alone is of little help when you overboost as soon as 3500 rpm. I'd love to hear more input as to corner cases that I surely haven't thought of yet. Lean AFRs is the next trigger I am working on.

Ricky SE3P

iTrader: (10)

The AEM 30-4900 gauge does both overboost and lean condition protection while also displaying both AFR and boost pressure. AEM might be replacing the product with a newer model as a quick couple of vendor searches led me to be unable to find inventory at retailers currently

Brettus

iTrader: (2)

Yeah ... I use the AEM failsafe gauge Ricki mentioned as a boost cut. But that only works on the wastegate so wont cut boost entirely (as there is still spring pressure to contend with).
Have thought about doing what you suggest but never got around to it . I think it would work better than what I currently have but do wonder if there is a possibility of overspinning the turbo.....

TeamRX8

iTrader: (25)

if you have a true standalone ecu then why do you need a BOV for an overboost protection strategy.
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TeamRX8

iTrader: (25)

but understand that the result is different between a turbo and a belt-driven SC. Because with a belt-drive the SC will spin relative to engine rpm when the BOV releases boost, but suddenly releasing the boost on a turbo is likely to result in the turbo to suddenly overspin when the compressor discharge load is suddenly released. Whether the driver lifts or not and with how much of reaction delay will figure into that turbo scenario.
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ciprianrx8

I don't have a standalone and at this point I never plan to run one - I need all the comfort features of the OEM one(cruise/TC/DSC/O2 sensor/OBD2 compliance). I'd love to have a load based ignition cut... not happening anytime soon.

The blow off opening to dump pressure is just a backup, of course the main method is to have the wastegate actuator receive any and all boost that exists. Surely the blow off alone is not the perfect way around it, but it surely helps for cases such as wastegates failing shut(pinched membranes/disconnected hoses/god knows what else).

At that instant where the load on the compressor disappears surely the turbo spins up quite a lot - I can't really hear it over the whistling the blow off makes but logic says so. Journal bearing turbos probably won't have time to spool up in such cases, but ball bearing ones probably do. Well, by 1-2 seconds that speed should go away as there are no more exhaust gases to keep the turbo going. My GTX3076R ran many times at no boost and redline.

Actually doing both(opening the blow off and pushing the wastegate open by any means) at the same time is the best of both worlds. One can also place a loudspeaker in parallel with the blow off solenoid and have that horn go off inside the cabin.

TeamRX8

iTrader: (25)

because it wasn’t spinning as fast as a new G-series turbo, which will obliterate a compressor wheel if the rpm limit on the far right of the compressor map it exceeded

and you were the one stating standalone ecu, so naturally I questioned that since there are numerous better and more effective strategies to address overboost for that scenario

it’s just not a good idea in general; just from the obvious perspective of not needing to blow off everything, just enough not to exceed the limit.

imo you’ll be better off keeping that in mind for assessing and evaluating a more effective solution, or not; entirely your choice.
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ciprianrx8

For my very particular setup I get this:



If this chart is anything to go on, then my turbo won't ever overspin. At ~NA flow levels and the 2-3 psi I still get with my BOV open, I'm pretty sure my turbo is not doing cartwheels. Even if I was pushing 350g/s at 0 pressure - still I'd reckon I am out of the woods.
Sure, not the most clever way to kill boost or bring a boosted engine back to its NA days; but it can and has saved me from exceeding my target boost on few occasions while I was adjusting my EBC.

Ricky SE3P

iTrader: (10)

One thing you may want to consider is that as the boost level rises, the compressor side of the turbo is effectively under load and posing additional resistance to spinning faster. Having the turbine speed way up providing enough flow to maintain a certain pressure at top end and then removing that load allowing it to rotate with less opposing force... hmm doesnt sound like a good idea.

I have a hard time imagining that automakers across the industry wouldnt all agree with and go with letting an engine pulling vacuum on a BOV if it wasnt the safest design, because the throttle plate is shut to alleviate positive pressure at the same time that the engine is no longer actively adding exhaust flow to spool the turbo therefore allowing the turbine to slow down. Thats what seems logical at least.

TeamRX8

iTrader: (25)

yep, if the load is suddenly removed it’s not easy to predict where the shaft rpm speed will rocket to in the 1/2 - 1 second range it might take someone to react and lift. And if somebody doesn’t lift … yikes 😬