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Thread: Boost Pressure in M939A2?

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    Max boost I see is 35psi. I have the fuel turned up high and she has a lot more pep. I run a 4in straight pipe and a TMG air filter. She will get hot, have to keep an eye on the EGTs. I can hit 1300F pretty easily. I like to keep it below 1200. I need an intercooler!
    1991 M923a2

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    Quote Originally Posted by Mos68x View Post
    Thanks Wes! That is quite hot for EGTs, I’m hoping to keep mine maxed at 800-900, but we shall see what will happen. But at least with this info I can properly size my nozzles. It will still be a guessing game with nozzles to a degree since I’ll have two separate water circuits, but at least this will help with a total size.
    You do know that these trucks stock will hit 1200 if you bury the throttle for any period of time? Im interested to see your results with W/M injection, but I highly doubt you will lowered the EGTs that much. Why not try running the truck the way it is? Ive always wanted to see some numbers, EGT mainly, with no aftercooler.
    1991 M923a2

  3. #13
    4 Star General 74M35A2's Avatar
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    Others have posted about 900F pre-turbo, stock, which makes sense. You had 1200F before and after turning up the fuel?
    CFO @ Portacharger

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    Quote Originally Posted by 74M35A2 View Post
    Others have posted about 900F pre-turbo, stock, which makes sense. You had 1200F before and after turning up the fuel?
    My motor always ran stronger than other stock trucks I drove. Theres a tag on it from Ft. Carson, not sure what they did. All the safetys were still on the motor when I bought it. I was surprised when I installed the EGT gauge in. I could hit 1200F and more completely stock with a load. I turned it up and can hit 1200F easily now, loaded, empty, uphill, down hill etc. Just have to keep an eye on the gauge. She sure does move now!
    1991 M923a2

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    Once I get my fuel delivery issue resolved I might try to see what my EGTs are, although I think I’ll most likely wait until after I get the water injection setup in place so that I don’t risk destroying this engine again. That way I can turn it on if it gets too hot
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    Mine hit 1200 stock empty, probe is in the exhaust manifold. I made sure to get temps before turning up fuel.

  7. The Following 2 Users Say Thank You to aziator For This Useful Post:

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    Default Boost Pressure in M939A2?

    I finally got my gauges installed on my stock, the way I got it from Uncle Sam 8.3.

    I only had a chance for a short, empty test run up to about 50 mph. Iím seeing 24psi of boost, and about 1215F pre turbo EGT, kind of scary! Now I cant wait to load it up for a proper test, and see just how hot Iíve been running the past few years loaded to around 50k on the highway, and also see if I have my top end power loss problem solved.
    Last edited by Jbulach; 05-05-2019 at 08:19.
    M925A2

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    Hauled a couple 12ton loads of stone today, max boost was right at 25psi.

    Air temp was 80F, coolant temp 195, uphill, lugging 4th down to 1600rpm would spike EGT up to 1275-1300, just before transmission would downshift and bring EGT right back under control.
    M925A2

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    Quote Originally Posted by Jbulach View Post
    Hauled a couple 12ton loads of stone today, max boost was right at 25psi.

    Air temp was 80F, coolant temp 195, uphill, lugging 4th down to 1600rpm would spike EGT up to 1275-1300, just before transmission would downshift and bring EGT right back under control.
    Myself if I am driving by the EGT gage I shift the automatic transmission myself before I let transmission do it. Same with a manual if you watching you temps then keep the RPM up higher than what you cruse at. If my temps don't run cool at close to the governor I turn down the fuel.

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    Yep, just wanted to see the worst I could do. Now that Iíve got a gauge and my baseline, I might start tweaking on her knobs.
    M925A2

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