Turbo talk

Discussion in '6.9L IH & 7.3L IDI Diesels' started by ISPKI, Feb 6, 2018.

  1. 03wr250f

    03wr250f Full Access Member

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    @kent01 I disagree with you there, 6.9 definitely needs studs for even 10-15 psi of boost in my opinion. they have 7/16'' head fasteners that are much weaker than the 7.3's 1/2'' fasteners.
    A stock turbo ip with a factory turbo or banks turbo will push 15 psi fairly easily. So right there you are in the territory for needing head studs on a 7.3 idi with at most turning up the pump. No lowering compression, nothing. It does not take much more work to get to 250 hp. granted that is some money spent, but not like you are talking. You could go about it one of two ways, a 110 pump or bigger on a banks or factory turbo will put you close as macrobb has shown, or you could intercool, bigger pump, and turbo, and bam you are there. It is also pretty dang reliable to do it the latter way. the only thing with doing either of those you need head studs to get to that mark otherwise it isnt horrendously difficult to hit 250whp in an idi.
     
  2. Thewespaul

    Thewespaul Supporting Member Supporting Member

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    Back in the late 80s the 6.9s had a reputation for blowing head gaskets stock, just like your modern 6.0l
     
  3. david85

    david85 Full Access Member

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    Touche^:kick:LOL

    Although the 6.0 only had 4 head bolts/cylinder, so I can't say I'm surprised it had issues. Even the powerstrokehelp guy says they are a time bomb without studs (probably exaggerating a bit, but still...)

    I get what Kent is saying about decompression though. Up to a point, it is a better way of getting more peak power, provided you have the turbo boost to play with. I could be made to settle on a 7.3 powerstroke, but I still prefer the mechanical reliability of an old IDI. I don't need 400Hp or even 300. 250 should be about right (maybe).
     
  4. Macrobb

    Macrobb Full Access Member

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    Starting and idle suffers though - you'll just get a lot of gray/blue smoke if you decompress it too far. IDIs need all the help they can get compression wise.

    250 is totally reasonable from a 7.3 IDI. It's doable without studs, but you run the risk of failure. I haven't failed yet, and it's been nearly a year of 250-rwhp use.
     
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  5. david85

    david85 Full Access Member

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    Absolutely, there are trade-offs. I'm not advocating 18:1 compression on an IDI. I shaved 20 thou of my 6.9 pistons but that was also to set my mind at ease with the resurfaced heads I'm running.

    Personally, I'd rather drill & tap a 6.9 block for 9/16 studs. I know some have tried but I'm not sure if any succeeded.
     
  6. ISPKI

    ISPKI Lumber Chucker

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    Good question. The HX40s are sitting on ~765CFM, HX35s are mid 600s. Should max out around 10PSI. Is it actually possible to calculate when it will start creating boost on a specific engine? What is an "appropriate" A/R ratio for a 7.3idi?
     
  7. ISPKI

    ISPKI Lumber Chucker

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    I have been looking at compressor maps for these turbos, I gather how most it works but how does one figure out what RPM the engine is spinning to get a ballpark of how much boos the turbo is making at a given RPM?
     
  8. ISPKI

    ISPKI Lumber Chucker

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  9. ISPKI

    ISPKI Lumber Chucker

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  10. david85

    david85 Full Access Member

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    Here's how I look at compressor maps.

    First, there's an airflow calculator here that works well:
    http://lovehorsepower.com/joomla/index.php?option=com_content&view=article&id=35&Itemid=49

    Based on the instructions, I entered 85% volumetric efficiency, 7L displacement (30 thou bored open on my 6.9), 3000 RPM redline (moose pump governed limit) and 250 RPM divisions.

    http://cybrina.mooo.com:8080/WebMod...oost=25&maxrpm=3000&rpmstep=250&Submit=Submit

    Next, I pull up the map for the turbo I'm thinking of using. In this case the GT3582R

    GT3582R mapped.JPG

    Then, plot 3 points. One at the start of the efficiency island, then another at the top of the island, or just shy of the desired wastegate setting, whichever is lower. The third point is plotted horizontally across to the right where the maximum airflow is reached. In this case, about 60lbs/min.

    Point 1:

    Appears to be at 1.75 PR and 33 lbs/minof airflow. Looking at the chart, this works out to 11 PSI @ 2500 RPM. Does that mean it won't spool below 2500 RPM? NO: only that it will spool most efficiently at that RPM.

    Point 2:

    I used an easy number like 2.5 PR for my max desired boost. Plotting the point the same way as before, we see that this results in 22 PSI @ 2500 RPM.

    Point 3:

    I'm assuming a wastegated turbo, so at this point, boost cannot climb higher, but airflow still climbs due to more engine RPM. This creates the horizontal line to the right, where the engine eventually reaches governed speed. Since we are no longer in the linear region of the turbo, efficiency is no longer at peak.

    Notice how engine RPM tends to follow the island consistently as you increase pressure ratio. This is how you can predict whether a turbo will spool at lower RPM, compared to higher RPM.

    Large A/R ratios favor higher RPM boost, while smaller A/R ratios work better at lower RPM. The tradeoff usually means one end of the engine RPM will suffer.

    The above example shows 0.7 A/R ratio, but they can sometimes go as low as 0.6 or 0.5. I haven't been able to locate those maps yet, however.
     
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  11. david85

    david85 Full Access Member

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    Now, unless I'm mistaken, the factory turbo/ATS 093 uses the H-trim compressor.

    Here's what that looks like (not 100% sure, but I think this is 0.6 A/R):
    H-3 Mapped.JPG

    Based on this, it's efficient starting at 7.5 PSI @ 2000 RPM. This fits, because that's what the factory wastegate was set to. Efficiency tops out at 16.5 PSI @ 2300 RPM, which seems to fit what others have reported on a healthy 093 setup.

    Next thing that jumps out at me is the upper limit of the peak efficiency island. It's right around 16 PSI, which matches what many report on these setups with the wastegate wired shut. There is still room to climb higher though. Indeed it seems 25 PSI attainable. This fits reports from Dave Sponaugle over on Ford Trucks.com from years back. Now, not everyone was able to get that high but I can see how it might be possible if you had enough fuel to burn.

    Last thing is the right hand limit of the map. Yup...its off the map which means nearing the limit of the turbo RPM. So this one is better for low end boost, but chokes near redline.

    All in all, the 093 is actually a pretty good setup.
     
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  12. Jason1377

    Jason1377 Supporting Member Supporting Member

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    As far are turbos go since there are so many options with them, would a small, meduim or large single double or even room for a triple one give any benefits to a daily driver that's not hauling big loads or trying to show off, compared to people who haul stuff of any kind.

    I get torque vs horsepower a basics of that but in a idi that's not stock turbo or modified for one, and how's that tie in to the og exhaust as far as pressure sounds n performance sorry long post
     
  13. ISPKI

    ISPKI Lumber Chucker

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    See I would have assumed that two small turbos would have less lag than a single large turbo since the rotation of the wheels are based on exhaust pressure rather than exhaust volume. In reading here, that may not be the case
     
  14. david85

    david85 Full Access Member

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    Well, yes, a smaller turbo will spool faster. But that is only one part of the story. A/R ratio will also influence lag time as well as where in the engine output range the turbo works best.

    Too small a turbo and it will choke at higher O/P levels. This is what the 093 does if you are running a hot pump and trying for more than roughly 16-20 PSI. Everywhere else, it should work well.

    Using twins is very difficult due to the lack of space under the hood of these trucks. But if each turbo is feeding off only half the engine, then the same sizing constraints still apply.

    Too small and they will spool great off the line but choke at high end. Too large, all you get is top end and endless lag at low end.

    You've also doubled the complexity of the system with more plumbing and more things to go wrong. I used to be a proponent of twins, but I'm not so sure its such a great idea any more. After reading more on verified VGT results, I'm getting cold feet on that idea too.
     
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  15. ISPKI

    ISPKI Lumber Chucker

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    So what A/R ratio seems ideal for the 7.3idi
     

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