Compound Turbo Questions - Dodge Cummins Diesel Forum
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post #1 of 3 (permalink) Old 10-05-2017, 12:32 PM Thread Starter
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Compound Turbo Questions

Hey guys,

With my current setup, im afraid to stand on the throttle all the way, as my turbo is pushing 38-40 psi and its the stock hx35. My EGTs are still relatively low, around 1000. I would like to put bigger DV's on it, and bigger fuel injectors, but it seems like my turbo is holding me back.

I have a question about compound turbos. How does the smaller turbo not over-spin once the bigger turbo takes over? Ive tried to research as much as i could on this, but it just doesnt make sense to me, especially how some people are using the stock hx35 as one of the two turbos.

Im thinking the best course of action for me is a bigger single turbo. Im not pulling a trailer usually, but i do throw a couple harleys in the bed of my truck every now and then and climb a few summits.

Is the hx40 a good upgrade or is that not big enough? Also, will i need to modify any plumbing, or is the intake location the same, so i can reuse my AFE?

Thanks in advance


95' 12v 331k, 47RH 4x4, KDP, 3kGSK, Afe intake, 4" Turbo back, 60hp fuel injectors, #100 fuel plate full forward, 64.5/71/14 Super B Special, Runs about 40lbs @ 1000* 15.3 MPG Avg - 33" Toyo MT on 20x12 MotoMetal w/ too much offset. Need bigger injectors
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post #2 of 3 (permalink) Old 10-05-2017, 02:41 PM
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In a compound set up , you would run a waste gate on your small turbo, sometimes both. The wastegate on your small turbo will be set relitively low, once the waste gate opens, it allows the air to bypass the small turbo and continue on to your large turbo. This helps prevent over spinning your turbo. Takes tuning

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post #3 of 3 (permalink) Old 10-05-2017, 02:48 PM Thread Starter
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Quote:
Originally Posted by jstevens101 View Post
In a compound set up , you would run a waste gate on your small turbo, sometimes both. The wastegate on your small turbo will be set relitively low, once the waste gate opens, it allows the air to bypass the small turbo and continue on to your large turbo. This helps prevent over spinning your turbo. Takes tuning

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Thanks! Thats much easier to understand.

With my hx35, the wastegate is internal. I have heard something about "overcoming the wastegate spring" and understand that with an external wastegate. Does this happen with an internal wastegate? The differance in my fuel plates from a #6 to a #100 results in the boost pressure going from about 26 to 38. Just fuel. Technically, if the wastegate was operating properly, wouldnt the boost stay the same, regardless of the fuel i threw at it?

In my example, is my wastegate spring being overcome? I dont have any kind of boost elbow or anything in my line from diaphram to turbo. I like the fueling i have, actually need more if my EGT is low, however i dont want my turbo to overspin. How can i get more fuel to my engine without raising the boost any more? Add another external wastegate? or do i have a problem somewhere?

95' 12v 331k, 47RH 4x4, KDP, 3kGSK, Afe intake, 4" Turbo back, 60hp fuel injectors, #100 fuel plate full forward, 64.5/71/14 Super B Special, Runs about 40lbs @ 1000* 15.3 MPG Avg - 33" Toyo MT on 20x12 MotoMetal w/ too much offset. Need bigger injectors
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