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Thread: 2015 6.7l ARP 425 vs 625

  1. Top Of Page | #21
    More Powa! RATLIN'HP's Avatar

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    Drive pressure is a ratio. 1 or a little over 1 to 1, is best. So if you hit 40 psi of boost, 40 to 50 psi of drive pressure is ok. If you hit 80 psi of boost, 80 to 100 psi of drive pressure is ok. But it's when you hit say 40 psi and have 75 psi of drive pressure that things go wrong.

    2015 Black Laramie CCSB 3500 SRW. Thuren Leveled With Fox 2.0 Shocks. Ride Rite Rear Air Bags With Wireless Airlift Onboard Air. 35" Toyos. All The Options Minus The Soot Cookers. RaceMe Ultra.

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  3. Top Of Page | #22
    More Powa! RATLIN'HP's Avatar

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    I may have gotten that ratio wrong LOL, but I think I explained it right.

    2015 Black Laramie CCSB 3500 SRW. Thuren Leveled With Fox 2.0 Shocks. Ride Rite Rear Air Bags With Wireless Airlift Onboard Air. 35" Toyos. All The Options Minus The Soot Cookers. RaceMe Ultra.

  4. Top Of Page | #23
    Basic Member E.mccarthy7018's Avatar

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    How a bout monitoring it? Is there something that can be hooked up to monitor this?


  5. Top Of Page | #24
    More Powa! RATLIN'HP's Avatar

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    Ya with a regular boost guage, but you need to coil like 10 feet of copper tube. Some use filters and needle valves to keep needle in boost guage from bouncing. Not sure where it goes in manifold exactly.

    2015 Black Laramie CCSB 3500 SRW. Thuren Leveled With Fox 2.0 Shocks. Ride Rite Rear Air Bags With Wireless Airlift Onboard Air. 35" Toyos. All The Options Minus The Soot Cookers. RaceMe Ultra.

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  7. Top Of Page | #25
    Basic Member brandonjansen's Avatar

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    I have ISSPRO 4th gen factory match gauges. They're the nicest ones available for the 4th gen Cummins in my opinion. Haven't had any issues with them at all other than the couple times I've had to clean out the drive pressure tube/sensor because it gets a little sooted up.



    The typical rule of thumb is that your drive pressure shouldn't be any more than 1.5x the boost pressure. So with that being said, with a factory VGT you shouldn't see any more than about 50-55 pounds of drive pressure under load. With good tuning that can be brought WAY down though. As I mentioned above, with Ray's tuning I have no issues with drive pressure at all; it's typically barely higher than my boost pressure. The picture below as pulling around 8500 pounds up a 7% grade at 100 km/h (60mph). 27 psi of boost, 29 psi of drive pressure, and 1200° pyro sustained up the hill. Definitely can't complain about that.


    (This picture was with the old style gauge pointers. The new ones are in the picture above. They match the OEM ones perfectly).

    I don't think I've ever seen more than 40-45 psi of drive pressure underload. The exhaust brake is a different story, I've buried my 60 psi gauge when towing but it's not near as much of a concern as there's no fuel or cylinder pressure from combustion involved in the equation.


  8. Top Of Page | #26
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    @brandonjansen
    Thank you! Very nice explanation!

    2015 Black Laramie CCSB 3500 SRW. Thuren Leveled With Fox 2.0 Shocks. Ride Rite Rear Air Bags With Wireless Airlift Onboard Air. 35" Toyos. All The Options Minus The Soot Cookers. RaceMe Ultra.

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  10. Top Of Page | #27
    Matt C Moore's Avatar

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    what tuning are you using w/ the 425's


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  12. Top Of Page | #28
    Basic Member brandonjansen's Avatar

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    Quote Originally Posted by Matt C Moore View Post
    what tuning are you using w/ the 425's
    Anything from a fairly tame tow tune through to max effort tuning for the stock VGT and injectors. All from Ray at @DoubleRDiesel.


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  14. Top Of Page | #29
    Matt C Moore's Avatar

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    Quote Originally Posted by brandonjansen View Post
    Anything from a fairly tame tow tune through to max effort tuning for the stock VGT and injectors. All from Ray at @DoubleRDiesel.
    @Double R Diesel you reckon this should be sufficient for me or think i need big boys LOL


  15. Top Of Page | #30
    DRD's Avatar

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    Quote Originally Posted by Matt C Moore View Post
    @Double R Diesel you reckon this should be sufficient for me or think i need big boys LOL
    425s are better than nothing.

    Ray
    Double R Diesel, LLC
    www.doublerdiesel.com
    info@doublerdiesel.com

    The Cummins Whisperer! John 3:16, Romans 10:9-10...Tuning for the Heart and Soul.


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