Best combo for compound

Discussion in '6.9L IH & 7.3L IDI Diesels' started by TurboSurge, Aug 11, 2018.

  1. TurboSurge

    TurboSurge Full Access Member

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    Looking at doing a compound setup. I was wondering the thoughts on a GT35 to a GT45? He351 to a gt45? Or what turbos would be best for this? Can’t happen right now but I’m planning to buy a 130cc or 150cc to push them. Yes I know I could have issues with heads but I think this would be really cool and different. The reason I asked about those turbos is because I already have them available. Would like some input please!
     
  2. kuskoal

    kuskoal Full Access Member

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    Got shaved Pistons? See what the PSD guys are running and go one step smaller. An H2E is a solid upgrade for a single charger on them, so maybe something around an s466 for a more modern turbo.

    The he351 is from a 5.9? Right? And might be a little on the small side, as the Cummins guys can use them for towing twins. These things need a LOT of air in comparison to the fuel being pumped in.
     
  3. Thewespaul

    Thewespaul Supporting Member Supporting Member

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    So any turbo configuration will work, but to have a good setup it takes math and research.

    With my 130 pump you want to have about 25-35 psi of boost to use that amount of fuel well. Ideally, a single turbo could achieve that well, but let’s explore the compound anyways, because we both know you’re going bigger and better in the future.

    I’ll start by laying out some goals as far as psi per rpms, for a starting place let’s say:

    1. 1500 rpms 5 psi
    2. 2000 rpms 15 psi
    3. 2500 rpms 20 psi
    4. 3000 rpms 25 psi
    5. 3500 rpms 30 psi

    Now with those psi goals in mind, let’s calculate the airflow needed to reach that boost level at each rpms, using this formula

    CFM=Displacement in Liters x rpms x volumetric efficiency x pressure ratio /5600

    We know all of these factors, but we still need to calculate pressure ratio. That is done by adding 14.7 to the boost pressure, and dividing by 14.7. So we end up with this for our cfm at the five rpms points.

    1. 196.5 cfm
    2. 395 cfm
    3. 576.9 cfm
    4. 792.1 cfm
    5. 1040 cfm
    Most compressor maps use lbs/min instead of cfm, so to estimate that, divide cfm by 14.5.

    Your manifold charger (your smaller turbo) you want to light off quickly and carry up until 2200-2500 rpms where the atmospheric charger starts to build boost. Using the numbers above, a tbp4 Garrett turbo would be perfect for you. Here is the compressor map with the first three points marked in yellow, you can see if right in the middle of the map, where you are at peak efficiency.

    14A39954-4773-4A50-9F29-838D859D9E02.jpeg

    This turbo is internally wastegated so you won’t have to worry about adding an external wastegate to bypass this turbo once it builds enough boost.

    Currently going for about $350 from Garrett: https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/172982628848

    As far as your atmospheric turbo, I would go with an s362 if you plan on changing it up later down the road once you have more fuel, or an s366 if you want to keep the compound setup.
     
  4. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    WHOA! This is WAAAY out of my league. Where's my aspirin? I now have the same headache that I have after staring at a wiring schematic for too long.
     
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  5. nitroguy

    nitroguy Registered User

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    THIS is what keeps me coming back to this site! Phenomenal stuff!!
     
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  6. TurboSurge

    TurboSurge Full Access Member

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    Great info Wes! Yes you know what is coming in the future but for right now I want to just have great power and to have something different. Having the diesel in my 78 is something different for sure but when I pop that hood and people see twins! Man that would be awesome!
     
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  7. Thewespaul

    Thewespaul Supporting Member Supporting Member

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    Happy to help, I think the 130cc is about the minimum amount of fuel I would run with any compound setup, and the manifold charger has to be quite small to make it responsive.

    Here’s a map of an hx35, he341, and he351 like what you were talking about, I marked all five pressure points in blue, and you can see none of the turbos can supply the airflow you need down low but start to pickup around 2000 rpms and they run out of flow up top, you would pretty much be exiting the efficiency range around 25-27 psi with the he351. 9D53ED79-3ACE-4027-BAC8-BD553A5C5DF2.jpeg
     
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