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Turbo configurations?

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Oldiron, Dec 15, 2019.

  1. Oldiron

    Oldiron Full Access Member

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    Dec 12, 2018
    Florissant, CO
    So after having a couple NA diesels (6.2 and a 7.3) and a few with bolt on kits (banks on a couple 6.2, and ATS on my 7.3) I will never have one with out a turbo, or at least not for long.

    What I am wondering is, would you get more throttle response from one turbo or would running 2 smaller, quicker spooling turbos remote located be more efficient?

    After reading about a guy running one remote turbo and what his boost #'s were and EGts, it seems like it would be a great set up. One on each frame rail and feed them together with a remote waistgate. I dont know much about turbos, just basics. Less heat, less cluster under hood. Yes more fab work and obviously 2 turbos.

    Figured if you have boost at idle and say up to 20 psi with 2 smaller turbos, in my mind you would use less fuel but have better throttle response.

    Does this theory work? Has anyone done this? What are your thoughts?

    Is this not as common because of fab work/cost?
  2. chillman88

    chillman88 Supporting Member Supporting Member

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    Feb 22, 2017
    Central NY
    @IDIoit is running twins on one of his rigs
  3. IDIoit

    IDIoit MachinistFabricator Supporting Member

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    Aug 26, 2014
    id say its the lack of people that own IDI's with fabrication skills.
    most people in search of high numbers have given up on this platform about 1995 lol

    not to say that there isn't many great fabricators out there, im saying most have moved on.

    the die hards out there that are innovative and do come up with their own stuff I hold in high regards.

    that said..
    I love these IDI's but they are not cheap to build if you look at it from the dollar/hp standpoint.
    so coin in the bank is another hurtle you must cross.

    ive been playing with this myself. I have a 63 ranchero on a 89 F350 4x frame.
    I decided I wanted to do something different and on the cheap, because I like low budget stuff, it allows me to build many vehicles on my income.
    I tried running twin GP38's. I did some things incorrectly. and learned some valuable stuff.

    while, those sounded cool as shat, it didn't perform.
    mind you, im on a stock 7.3. with head bolts and a stock turbo pump.

    I swapped to .81 quick spool housings, and it got a little better, but I only boosted around 10 psi at WOT.

    ditched them and went with t04e's
    they spool a lot better.
    at WOT im pushin 25+ psi
    I have about 2600 into the turbo set up.
    all still on a mock up block.

    as far as throttle response, its all about the condition of your IP.
    gov, and fuel are the areas that you can play with.

    how crafty, and how much money do you have. is the question :)

    ive got some mony tied up into the new engine that will be going in beginning of the year.




    saburai, quickster and Kizer like this.


    Likes Received:
    Feb 5, 2010
    edmond, ks
    The biggest difference that I can see here is turbo location. Yours are on the manifolds, while Oldiron is talking about putting them down on the frame rails. I don't think you'll see much spooling issues with your location.
  5. aggiediesel01

    aggiediesel01 Full Access Member

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    Dec 29, 2016
    Houston, TX
    Correct turbo sizing for an application is where you can minimize lag and maximize efficiency. Two small turbos might or might not spool faster b/c while individually they have a smaller rotating mass than a big one they’re only being driven by half the engine unless they are in series. Each turbo design has an air flow map describing how much air volume can be created and where the turbo operates most efficiently. IDIoit’s problems with the GP38s were related to the fact that the GP38 turbine was designed to be driven by the entire 7.3L exhaust volume not half of it. It sounds like the new turbos he has are sized more appropriately for 3.65L or half the engine. Another problem with remote mounting locations, getting the lube oil back to the engine sump frequently creates problems.

    It’s important to remember that turbos are more than just double ended fans pushed by the exhaust. They need the energy of the expanding exhaust gasses to be most efficient so putting them as close to the manifolds as possible is best. Once the gasses have cooled, they have lost their energy, aren’t expanding, and can’t do any more work. Engines are just air pumps, same quantity of “air” out as in (accounting for changes in pressure, volume, and temperature). The energy in the fuel is used to heat the air which rapidly expands pushing the piston down and creating work but at relatively low efficiency because it’s not feasible to let the gasses expand until they’ve given up all their energy. So, the leftover expansion of gasses not able to be used pushing the piston down can be used to push the turbine of a turbo because the gasses are still expanded as they leave the combustion chamber and enter the exhaust duct. This is the real reason to wrap/coat exhaust manifolds and piping leading to a turbo, to keep the heat in and keep the gasses expanding and expanded as long as possible. If the exhaust temperature entering the turbine was the same as the intake charge then no work could be done by the turbo, it wouldn’t generate any boost and would only be a drag on the system.

    If you had a thermally ideal exhaust duct that could theoretically keep all the heat energy in the exhaust pipes until they leave the turbine no matter how far away then it wouldn’t matter how far the turbo was from the exhaust ports but the heat energy is being lost in massive quantities as soon as it escapes the exhaust valve (think how hot the exhaust manifold is).
    Last edited: Dec 21, 2019
    saburai and IDIBRONCO like this.

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