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  #1  
Old 04-01-2021, 01:29 AM
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Max Boost for 617?

What is the the boost blow off pressure for the 617 turbo diesels? I am getting 7.5-8.0 psi before the waste gate opens. I thought stock was supposed to be 10 psi.

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  #2  
Old 04-06-2021, 12:37 AM
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The wastegate opens at 9psi on all stock OM617 of all years. The safety switch closes at 16psi.
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  #3  
Old 06-17-2021, 12:02 AM
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editing for clarity, the following is wrong:

"Stock is specified to be 7-9psi and the overboost alda switch engages at either 12psi or 15psi."

Last edited by nastala; 06-18-2021 at 08:59 AM.
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  #4  
Old 06-17-2021, 11:57 AM
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Quote:
Originally Posted by nastala View Post
Stock is specified to be 7-9psi and the overboost alda switch engages at either 12psi or 15psi.

Incorrect.

Fun fact: Though specified by Mercedes at 10-11psi stock, ALL engines shipped set at 9psi.
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Max Boost for 617?-screen-shot-2021-06-17-09.54.42.jpg   Max Boost for 617?-screen-shot-2021-06-17-09.56.22.jpg  
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  #5  
Old 06-18-2021, 09:06 AM
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Interesting. I looked around to see if I could find where I got the numbers, and found that MB mentions 1.7 bar of boost in their SAE paper, which is what I get right now running with no wastegate. I've attached the piece which isn't relevant to the question of factory boost but is interesting anyways. I also have the full SAE paper if anyone wants it, PM me.
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  #6  
Old 06-18-2021, 01:18 PM
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My reading of the excerpt from the SAE article is that they are talking of the wastegate controlled engine, and the 'boost pressure' is the total pressure being exerted on the cylinder walls.
(1.0 bar from the atmosphere and the additional air charge of 0.7 bar for a total of 1.7 bar)

From the graph of boost vs engine speed if you subtract 1.0 bar the engine performance makes sense.
[Turbo lag from 1000 rpm (with 0.2 bar) to 2000 rpm with (0.7 bar), and wastegate controlled boost of 0.7 bar (from 2000 rpm to 4000+ rpm)]
Just a little different interpretation of the definition of boost pressure (in the SAE article) from what we typically define as boost pressure.

Essentially the same graph, in greater detail (with boost expressed in millibars, as the additional amount of pressure over over atmospheric pressure) is attached below.
It is from the W123 FSM, Section 09-450 Functional description of exhaust gas turbocharger with aneroid compensator, on Page 4 of the pdf.
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Max Boost for 617?-w123-fsm-section-09-450-page-4-figure-3.jpg  
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  #7  
Old 06-20-2021, 11:16 AM
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Quote:
Originally Posted by nastala View Post
MB mentions 1.7 bar of boost in their SAE paper, which is what I get right now running with no wastegate.

First, 1.7bar absolute pressure, not gauge pressure.
That is the 0.7bar (psi) specified in the service manual.


Second, running with the wastegate closed is extremely bad. Its there for a reason, that turbo is not designed to operate without a wastegate, you're severely overspeeding the turbo and putting your engine at high risk of damage when it will fail.
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  #8  
Old 07-05-2021, 05:32 PM
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Quote:
Originally Posted by Felching View Post
First, 1.7bar absolute pressure, not gauge pressure.
That is the 0.7bar (psi) specified in the service manual.


Second, running with the wastegate closed is extremely bad. Its there for a reason, that turbo is not designed to operate without a wastegate, you're severely overspeeding the turbo and putting your engine at high risk of damage when it will fail.

Probable, judging from the compressor map I am slightly above or at the maximum speed of the compressor wheel marked on said map. Planning on installing a boost controller later to bring it to heel at 15psi or 17psi before I install a HE221W+intercooler setup.

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