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Compound Turbo Thread

Posted by RWD4G63, Oct 31, 2012

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  1. LandSpeed-DSM

    LandSpeed-DSM Proven Member

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    Chicago, Illinois
    I can't tell if there is some hyperbole in your position here because you are upset that I am disagreeing with you or not.. but lets go through this real quick:

    This statement:
    Is more or less true. From a perspective of complexity and efficiency. However it is sometimes the case where when match real well, some have demonstrated a small increase in total flow than otherwise be possible out of the LP stage on its own. The 16G and the 60-1 from Paul's old setup.. I think Ricky has it now. Not sure if that configuration was retained though.

    There are more than a couple of reasons to run a compound. Area under the curve being a big one.. bringing up effective displacement to run a turbo that motor would never have been able to light in the first place (like a 96mm turbine on a 2.0, as cited earlier), using a smaller turbo to get on a converter that is tighter than would otherwise be possible in a class where nitrous is not allowed, or from an OE consideration.. help a diesel pass stringent emission standards by keeping airflow up at lower revs/between shifts when fuel is introduced.

    On to your point on John's car - It's important to remember (in case you haven't) that the HX52 is a big mofo, I run one as well.. so with sufficient charge cooling, stable fuel and aggressive tune put 650awhp @ 27psi by its' self well within the range of what I would expect. John's seemingly efficient intake and exhaust routing combined with a nice big cam help a good bit in keeping boost that low, but its the massflow as a function of demand that is what makes the power, not necessarily a given boost pressure. There is one HX52 powered 5MT DSM that made ~770awhp @ 30-31psi FWIW

    If you are logging boost and drive between stages, you will see the pressures and proportions are not static. This concept, as you put it:

    Is indeed a good idea, and what some folks already try to do. This is because the bypass from the HP turbine is hotter and faster moving. You are not introducing more massflow, it was already there. You would just need a lot of valve area for when the big charger comes on and needs to breathe through the gate, how much it needs to go through the gate depends on the size of the HP turbine, and how much air you are asking of the LP compressor.

    Wastegate manipulation with electronic control certainly would be advantageous. Recirculating the HP gate for this purpose is a good idea, dumping the LP gate to atmosphere is too and for the same reason you would on a single turbo.

    Dumping the HP gate would be a mistake.. you need this to provide the energy to sustain the LP turbine. You just need to size the LP turbine like you would for a comparably sized big single on a bigger motor.. the LP turbo after all doesn't know or care what it's attached to. :)

    Find your corrected flow on the system concerning just the HP turbo and the motor, and plot that on to a a bigger turbo's compressor map. It's the same way you would choose a single for a bigger motor.

    From my perspective, yes this is true if you are just going for a power goal and don't have a need for any of the uses mentioned earlier (emissions/converter/nitrous/etc) It's precisely what I am employing it for on my SOHC 1.5L Compound project. A significantly larger LP turbo than would otherwise be usable.

    If you want to use something like a 50 trim @ 2.0PR as your small turbo to determine spool, and you plan to make in the neighborhood of ~1100whp you are going to have a real tough time because that is going to have you looking an ~88mm compressor and the equally gargantuan turbines those come attached too.

    This goes back to the same example from earlier.. ~4:1PR on a 67mm as a single will do mid-upper 800s maybe 900 depending on fuel and other details.. but if you are running 2:1 on a 16G, and then 2:1 on a 75mm to make your total of 4:1 in the manifold, where does that put you on the LP turbo's map?

    Just turning up the boost won't help at that point. Especially on a high rpm, high VE motor. Several real world examples back up the math. I'm not just being argumentative for my own entertainment.

    This is where that idea of manipulating the wastegate scheme and PRs on each stage comes into play.

    I don't mind the rambling at all, these staged turbo discussions are some of my favorites and inevitably they will occasionally bring up things all parties involved may not have have considered.
     

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  2. 95GSXracer

    95GSXracer DSM Wiseman

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    I still insist that there is no way to outflow the atmospheric turbo. You can't "pull" air through one turbo with another one, and there is only atmospheric air entering the primary's inlet. That being the case, you are indeed limited to the capacity of the large turbo, which can indeed be handicapped by compounding if the PR is low, but there are still many good reasons to do it in a few cases, IMO.
     

    Drag Race Build 2K  5

    1992 Eagle Talon TSi
    7.961 @ 171.10 · 1G DSM
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  3. T-mun

    T-mun Proven Member

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    South East Asia, Asia
    Just wondering if any body have tried this on a colt chasis, must be a darn tight fit.
     
  4. Sp1kE

    Sp1kE Proven Member

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    stratford, ON, Canada
    Update on my iat issye.

    My water pump motor was not seated correctly so I don't think the water flow was there. I also installed 2 turbo blankets. Before I was seeing iat's of 140. Now at the same psi. They are peaking at 107. Ambient was a bit cooler. But it is a drastic drop. I still think I can drop it more with heat shields and wrapping. And then let the meth do the rest for anything over 20.
     
  5. RWD4G63

    RWD4G63 Proven Member

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    I still think there is a lot of overthinking in this thread. Put two turbos on, run them both in there efficiency zones, and you should at least make as much power as the bigger one at it's pressure. You'd have to have a pretty small "large" charger (kinda like Sp1ke haha) to run it off the map into choke.

    Good to hear man! Let us know how the tuning goes.
     
  6. LandSpeed-DSM

    LandSpeed-DSM Proven Member

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    Pick a turbo. Now pick your PR.

    Follow that PR horizontally to the edge of the map where it chokes. Draw a line straight down.

    That is the most it will flow at that PR/shaft speed, period. If that PR is not at the part of the map extending farthest to the right, then you will not flow as much as it possibly could at a different PR.

    Just like any turbo in the history of ever LOL

    No over-thinking needed. ;)
     

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    1992 Mitsubishi Eclipse GST
    · 1G DSM
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  7. RWD4G63

    RWD4G63 Proven Member

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    The problem with this is that there is no way to accurately determine the engine's airflow needs at that pressure ratio with a compound setup.

    Taking the S475 as an example, at 2.4PR, it could flow as little as 40lb/min, or as much as 100lb/min at that pressure.

    Unless you have a turbine speed sensor or actually go through and calculate the engine's VE coupled with the smaller turbo, you have no way of knowing if you're putting the turbo into choke.

    The only way to do this is turn the boost up until the fuel doesn't allow any more.
     
  8. 95GSXracer

    95GSXracer DSM Wiseman

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    LaRue, Ohio
    Take your total airflow and divide it by the PR of the large turbo to plot the small turbo on its map. That gets you closer than most of us need to be. The large turbo can be plotted just like any other turbo. In my case the map shows a limit of 90-91 lbs for my large turbo at the low PR it runs, and my airflow measurement maxes out around 92-93 lbs/min. Pretty darn close considering that was on AEM speed density and I was calculating mass flow from AFR, IDC, and fuel SG. In short, you can expect to max out the turbo right about where the map ends. In some cases you can go beyond it, it depends on how the map was generated, but most end right about where the turbo will in reality. Even if you don't believe the exact number, at still shows the trend that max airflow is lower at lower PRs than it is at high PRs.
     

    Drag Race Build 2K  5

    1992 Eagle Talon TSi
    7.961 @ 171.10 · 1G DSM
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  9. viperlp01

    viperlp01 Proven Member

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    Kalamazoo, Michigan
    Kevin did you ever try like 10-15psi out of the primary and make the 75mm do work? Its just seems contradicting to all the arguments that I picked up 100hp from 35psi(550) to 41psi(618) to 44ish psi.(648)(all the boost increase was from the big). I want to get the new converter in and some testing before I turn it up more but I would love to test turning the small down as the big starts to light up. Should decrease back pressure and I would imagine power levels would be extremely similar with less boost pressure.
     

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    1997 Eagle Talon TSi AWD
    9.737 @ 140.310 · 2G DSM
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  10. 95GSXracer

    95GSXracer DSM Wiseman

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    I never did, partly because I was on springs only for the secondary, and was adjusting boost at the big turbo only, and partly because the small turbo was already borderline on its map. Moving the PRs around would have helped the primary, but hurt the small turbo. I think the only way to make that work well is to completely bypass the small turbo, and that would take a lot of wastegate. Otherwise you're going to run the small turbo right off the bottom of the map.
     

    Drag Race Build 2K  5

    1992 Eagle Talon TSi
    7.961 @ 171.10 · 1G DSM
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  11. viperlp01

    viperlp01 Proven Member

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    I would imagine that the 2.5" pipe for my 60mm wastegate can move a shiz ton of exhaust by it. I might take some spring out of it to see what the difference is. It is currently rocking a 17psi spring but holds 18psi and the weird thing is that is rock solid. The only turbo that had trouble holding a steady boost curve was the secondary.

    Am I wrong in saying after the large turbo is at full pressure you no longer need to run any pressure in the small(almost impossible I know). Does the small turbo's efficiency map actually affect the airflow if its below its efficiency range. With that H1C at 18psi it doesn't seem to be in its sweet spot but still seems to work fine.
     

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    1997 Eagle Talon TSi AWD
    9.737 @ 140.310 · 2G DSM
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  12. caged

    caged Proven Member

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    Does anyone know anything about this setup?
     

    Attached Files:

  13. 94awdcoupe

    94awdcoupe Proven Member

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    were you measuring temps? 400 sounds about right for TOT on a 16g at 30psi. . so those temps are okay with methanol ? thats wild. how much drop in temp was there moving to bigget stock frame turbo?
     

    Street Build 3K  0

    1994 eagle summit wagon JDM RVR swap
    automatic · 4G63t Swapped

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    1993
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  14. turbotalon1g

    turbotalon1g Proven Member

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    Land speed, what are you running on your compound setup? How is it working?
     

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    1991 Eagle Talon TSi AWD
    11.333 @ 119.94 · 1G DSM
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  15. RWD4G63

    RWD4G63 Proven Member

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    The sensor maxed out at 300* at about 5000rpm. The 16G was spiking to 43ish psi. He doesn't even run an IAT now, as it was screwing with the load map in Link.

    Man, looking at my old compound setup really makes me want to mess around with it again. Should have stuck with it. :ohdamn:
     
  16. Sp1kE

    Sp1kE Proven Member

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    Well I have ran into problem after problem, still trial and error with this setup.
    I have swapped out to a HX35 with the larger turbine housing. The car seemed to accellerate "smoother".
    I pulled off a 12.8 with less than 20psi on stock cams, with a notchy trans.

    But Things I have noticed:
    -No matter how much heat wrapping I do, the intake temps still creep to 140ish during WOT redline pulls. But with everything under the hood cooler, the temps start dropping much faster on decel. (maybe too small of a water/intercooler? or Really need meth to function over 20psi..)
    -Coolant temps on a half rad are kind of under controll with everything wrapped. (Ducting will be key for next season)
    -My turbo to turbo exhaust pipes gained some cracks along some of my sh**tier welds after being wrapped.
    -Boost control is random, may-be the pressure regulator im using for the large turbo. but a good boost controller is definatly needed for compounds...

    Question:
    I am thinking of re-doing my turbo-turbo piping for next season.
    Would there be any benefit to increasing the exhaust size to 3inch from 2.5?
    Or would the velocity help spool the large turbo, and then when the wastegate opens, aleviate enough of the pressure until redline?

    Opinions?
     
  17. LandSpeed-DSM

    LandSpeed-DSM Proven Member

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    Boost is only 20psi in the manifold? What is your primary stage contributing to that? You are probably in very inefficient parts of both maps.

    Even with that said, 140IATs at only 20psi is telling me you need a better charge cooler.
     

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  18. Sp1kE

    Sp1kE Proven Member

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    Primary is doing 16-17ish. And the rest is done by the secondary. I have been trying to keep them around the same for tuning purposes. But the secondary is doing the last 3-4psi.
    I guess I could look for a larger water to air cooler.
     
  19. 95GSXracer

    95GSXracer DSM Wiseman

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    16-17 and 3-4 definitely aren't the same. :D To split the PRs at 20 psi you want more like 9 psi from the big turbo and the remaining 11 psi from the small turbo. Assuming comp efficiencies of ~60% at those boost levels, and 80% IC efficiency, I get outlet temps of 136 degrees. Running low boost with compounds is a pain in the ass.

    Bringing boost up to 45 psi and splitting the PRs (~17 psi from the big turbo, ~45 psi total), the compressors get into a better part of the map around 2:1 and the same IC efficiency air temps only come up to 155 on my spreadsheet. I was seeing about that with an ebay air to air on my setup. In other words, I wouldn't be afraid of turning the boost up slowly and seeing what happens.

    For boost control I used the springs only for the small turbo, and a Hallman MBC for the big turbo. How are you using your regulator, an what is controlling the small turbo?
     

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  20. Sp1kE

    Sp1kE Proven Member

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    Humm, I am somewhat confused how you are phrasing things.
    If both wastegates are set at say 9psi, like you said I should run on the big turbo. and I do a pull, the total psi is 9psi.
    So it sounds like you are saying if i want to run 20psi, I should be turning up the small turbo's wastegate, until I reach 20?

    For boost control is currently setup:
    Small turbo wastegate gets its source from the manifold, and use a simple ball and spring.
    The large wastegate gets its source from the manifold aswell, and plugged into the lower port. Then I have a pressure regulator taken from the same source, and have been applying pressure to the top port on the big wastegate. I have not been touching the ball and spring, and only using that pressure regulator to raise and lower the large turbos boost.

    Should it be setup differently?




    Once I get some meth flowing just to be safe, I hope my intake temps will stay inline when raising the boost. Everyone keeps telling me the same thing, that i am in an inefficient part of the map.(hope you are right :) )
     
  21. LandSpeed-DSM

    LandSpeed-DSM Proven Member

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    Wastegate springs with reference from manifold on the HP (small) turbo, Boost controller on the LP (big) turbo. This can be referenced either between stages or also on the manifold.

    There are a ton of schemes that can be used here. Some work better than others on a specific application.

    You want to split the work between both turbos.. that is the whole reason for doing this in the first place, unless you are trying to run an impossibly large turbo for a given displacement/rpm.

    You are in a bad part of both maps. Boost is too low on both stages, and too low in general to make a two stage compressor system worth while. Plot where you are on the HP Compressor's map.. now overlay that onto the LP Compressor's map. That is basically where you will land before/during spool of the LP stage.. that is the demand flow of the superficially increased engine size the LP Turbo "sees."
     

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  22. TajMan

    TajMan Proven Member

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    Salt lake City, Utah
    I LOVE THIS

    I recently was introduced to this new turbo world of compound, and I must build one.

    I currently have a 91 Talon with a 'frank level III' 20G and SBR front mount and DSMlinkV3, and I'm acquiring another 91 GSX that needs a motor built, and I have a 2.3 stroker shortblock all built up ready to use with wiseco pistons and eagle rods and a 4G64 crankshaft. I question if I want a head built with +1mm oversize valves on the intake side or if that difference is negligible. I have a set of 264/264 cams I'll prob pull out of my Talon because I'm selling it, is 264/272 a good cam choice for my stroker?

    Even if I put the stroker motor in the new GSX for now.. I want to use it eventually in a long-term race car project of mine, a '77 Lancia Scorpion I'm building with a turbo mitsu engine! (mid-engine). Weight would not be an issue, space is an issue because the turbos would be ahead of the engine towards the car's middle right behind the driver's back/'firewall'.

    Maybe I can fit things having turbo(s) more over the transmission. My goals are a 600hp street car, and quickest-spool possible.

    I'd like to hear what you guys recommend for compound turbo sizing on my 2.3L. I was thinking like a 14B and a HX40? I'd say a 15G, but a TD05 turbo would be superior primary, right?
    I'm not as trained on turbo sizing or been active in the community in recent times.
     
  23. Derail20T

    Derail20T Proven Member

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    Instead of creating a new thread, I'm bringing this one back up to discuss my compound turbo project. I recently acquired a compound turbo setup that was originally on a mirage. It consists of a bw s366 primary turbo and an FP 68hta secondary turbo, 2 60 mm wastegates, 1g exhaust manifold with wastegate provision welded on and all of the exhaust and intercooler piping. I haven't started putting it together but I don't think that the setup will fit like it did on the mirage so I will likely have to fab up some new piping to install it in my automatic '91 tsi AWD.
    I have to decide whether or not I want to use the 68hta as my secondary turbo or go with something different. My main goal with this setup is to run 10's and be able to spool up the turbo's and load up my converter without nitrous. Currently I have an old school FP red installed on my car and need nitrous to get up on the converter to get a decent launch so it's not too great on the street. As I was saying, I am thinking about using a different secondary turbo. It will need to have a dsm housing I am wondering if a 14b would work well with its quick spool or should I get a small or big 16g. I just don't know if the 68hta will spool quick enough for my liking. The one problem that I could see with using too small of a secondary turbo is that the turbine housing could become a restriction in upper rpms. However I will be using a large 60 mm wastegate to bypass the housing so hopefully it won't be an issue. I was also thinking of using an internal wastegate on the 14b in addition to the external wastegate. I have 2 14b's in my possession so that's not an issue and one of the reasons that I am thinking about using one. I could also send one of the 14b's out to get made into a 16g. I just don't know if the 68hta is too big of a secondary turbo. I realise that the 68hta is a great turbo but I could always sell it to recoup some of the money that I spent on the setup or save it to use on another project. Let me know what you guys think!
     

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    1991 Mitsubishi Galant VR-4
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  24. rrussell

    rrussell Proven Member

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    I think you would be fine with the 14b as a secondary HP turbo. I'm running a 13g for my secondary HP turbo and a Old School HTA Red 61mm inducer 35r wheel with the 8cm housing for the primary LP turbo. It gets up on the stock converter in less then 2 seconds, and reaches max boost instantly.
     

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  25. Derail20T

    Derail20T Proven Member

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    That's good to hear. Do you have any issues with such a small turbine housing? What type of wastegate setup are you running? If I could get away with running the 14b and just using a 60 mm external gate it would be less work fabbing the piping since it's already setup that way...
     

    Street Build 426  1

    1991 Mitsubishi Galant VR-4
    319 whp · 288 lb/ft · Galant VR-4

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    1991 Eagle Talon TSi AWD
    10.84 @ 124.02 · 1G DSM
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