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Old 07-08-2019, 05:24 PM   #1 (permalink)
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Default Please school me on wastegate pressure

I always thought/believed that a turbo's wastegate would only open when the boost soleniod diverted some engine boost to the wastegate, and even then the engine boost pressure had to be an amount greater than the wastegate setting (eg 6lbs of boost for an OEM wastegate). When open, the wastegate would reduce the exhaust gas going to the hot side so the turbo won't over-spin. I was happy in my simple wastegate belief/understanding but I've read posts about wastegates where the user says:

1) "I'm running my boost at wastegate pressure". WTF does that mean? Does it mean you are running only 6lbs of boost? In other words, you've set your boost pressure to a max of 6lbs?

2) "My wastegate can hold 16lbs". WTF does that mean? Why do you want a wastegate that doesn't open when the standard 6lbs of boost pressure are sent from the wastegate solenoid? Is this so that your wastegate doesn't unexpectedly fly open when you are running lots of boost?
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Old 07-08-2019, 05:58 PM   #2 (permalink)
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Default Re: Please school me on wastegate pressure

The wastegate rating is the approximate amount the wastegate will open if it is supplied boost directly without a boost controller in the way. A 15 PSI wastegate spring may crack at 13 and be fully open at 15, but testing on your combo is the only way to really know what effective boost you'll see. This is what people mean they are running "wastegate" pressure.

Once you start to interrupt the signal you are over wastegate pressure. The reason for stiffer springs is at ratios much higher than say about 3 times your spring pressure the gates will start to blow open if you have it set higher.

That's not to say people haven't run more than 18 psi on stock 6 psi springs, but you will run into issues holding the wastegates shut at some point, especially with the extremely high exhaust back pressure you will see at high boost and a stock frame turbo.
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Old 07-08-2019, 06:30 PM   #3 (permalink)
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Default Re: Please school me on wastegate pressure

As Chris described - it's more of a mechanical limitation of the spring vs. an air pressure signal, thing.
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Old 07-08-2019, 06:50 PM   #4 (permalink)
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Default Re: Please school me on wastegate pressure

thanks guys!

Am I correct in saying that the stock (OEM) wastegate solenoid applies boost pressure to the small connection on the wastegate? Or is the wastegate solenoid actually applying vacuum to the small connection on the wastegate?

Chris, I didn't realize that some guys don't connect to the small connection on the wastegate and the wastegate just opens itself, did I read that correctly?
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Old 07-08-2019, 08:41 PM   #5 (permalink)
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Default Re: Please school me on wastegate pressure

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Originally Posted by gawdzinner View Post
thanks guys!

Am I correct in saying that the stock (OEM) wastegate solenoid applies boost pressure to the small connection on the wastegate? Or is the wastegate solenoid actually applying vacuum to the small connection on the wastegate?

Chris, I didn't realize that some guys don't connect to the small connection on the wastegate and the wastegate just opens itself, did I read that correctly?
Its applying boost (positive pressure) to open it.
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Old 07-09-2019, 10:03 AM   #6 (permalink)
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Default Re: Please school me on wastegate pressure

Quote:
Originally Posted by gawdzinner View Post
thanks guys!

Am I correct in saying that the stock (OEM) wastegate solenoid applies boost pressure to the small connection on the wastegate? Or is the wastegate solenoid actually applying vacuum to the small connection on the wastegate?

Chris, I didn't realize that some guys don't connect to the small connection on the wastegate and the wastegate just opens itself, did I read that correctly?
Just to muddy the water a little more... The stock system works by feeding constant boost pressure to the gates via a metered orifice, and the solenoid increases boost by bleeding off some of that pressure.
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Old 07-09-2019, 11:42 AM   #7 (permalink)
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Default Re: Please school me on wastegate pressure

thanks again guys, based on what you've provided, here is what I have gathered for the answers to my 2 questions...

1) "I'm running my boost at wastegate pressure". WTF does that mean? Does it mean you are running only 6lbs of boost? In other words, you've set your boost pressure to a max of 6lbs? Yes, it means that there is no boost control soleniod so the wastegate will fully open when the boost pressure exceeds the limit of the wastegate spring.

2) "My wastegate can hold 16lbs". WTF does that mean? Why do you want a wastegate that doesn't open when the standard 6lbs of boost pressure are sent from the wastegate solenoid? Is this so that your wastegate doesn't unexpectedly fly open when you are running lots of boost? Yes, similar to question #1, upgrading the wastegate spring rate will reduce the chance of the wastegate "partially" opening.

Last edited by gawdzinner; 07-09-2019 at 06:00 PM.
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Old 07-09-2019, 05:54 PM   #8 (permalink)
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Default Re: Please school me on wastegate pressure

Technically, the stock boost control setup feeds plenum pressure (or vacuum) to the wastegates (not “boost pressure”), and the stock solenoid bleeds some of that air back into the intake when the ECU energizes the solenoid to raise the measured load towards the current load target.

With that design, if the solenoid fails then you end up with lowered boost instead of increased boost.
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Old 07-09-2019, 11:14 PM   #9 (permalink)
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Default Re: Please school me on wastegate pressure

Quote:
Originally Posted by mjannusch View Post
Technically, the stock boost control setup feeds plenum pressure (or vacuum) to the wastegates (not “boost pressure”), and the stock solenoid bleeds some of that air back into the intake when the ECU energizes the solenoid to raise the measured load towards the current load target.

With that design, if the solenoid fails then you end up with lowered boost instead of increased boost.
Stock system is fed off the Y-pipe... Never sees vacuum. Solenoid is normally closed, and feeding full boost pressure to the gates. ECU can cycle the solenoid and bleed off the boost signal pressure, and increase overall boost level.
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Old 07-10-2019, 05:29 PM   #10 (permalink)
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Default Re: Please school me on wastegate pressure

thanks for the further responses!

I was not really questioning how the stock boost solenoid gets it's positive boost pressure "reference" for determining when open the stock wastegates (eg at the Y-pipe or at the upper plenum), or how/if the stock boost solenoid bleeds off positive boost pressure (positive pressure, not vaccuum) prior to applying positive boost pressure to open the wastegates. Though it's all good information, I'm not smart enough to understand how to apply what you guys provided, but i was trying to make sense of it by looking at the picture in Blackstealth's LCDBC pdf, but again I'm not smart enough lol

the LCDBC picture looks like the stock boost solenoid sends it's positive boost pressure to the front/rear wastegates in addition to the Y-pipe all at the same time (3-way splitter?), while getting the positive boost pressure "reference" from the upper plenum, is that what you guys are describing?

lcdbc instructions for installing the boost controller are in this PDF-->http://lcdbc.xp3.biz/InstallationEBC.pdf
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Please school me on wastegate pressure-lcdbc_pic.jpg  

Last edited by gawdzinner; 07-10-2019 at 05:50 PM.
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