PSI D blower psi

Discussion in 'Pit Buzz' started by lambfunnycar, Dec 5, 2009.

  1. lambfunnycar

    lambfunnycar New Member

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    What are some real numbers people are seeing on a PSI D? I have heard 52 to 62. That is a big gap! I do not know if I believe the 62, but tell me if I am wrong. This is at the current NHRA rules of over drive, not the old.
    Thanks,
    Todd Lamb
     
    #1
    lambfunnycar, Dec 5, 2009
  2. Dave Germain

    Dave Germain New Member

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    I know that everyone wants to know boost numbers including me but they aren't that simple. For an example take a roots top fuel blower-lots of those guys say they get 48-52 pounds of boost from their 14-71 Roots type blowers but you have to keep in mind it takes upwards of 800 hp just to turn their blowers at top RPMs. On the other hand in PSI screw type blowers I personally have seen numbers on mine from 42-62. The 62 number was almost immediately followed by a explosion as more than one rod exited the block. Another factor to keep in mind is the worse the heads,cam, and valvetrain flow the higher the boost numbers you will see. So high boost in a inefficient motor isn't a good thing either. Another factor to keep in mind is atmospheric conditions. A blower at sea-level makes much higher boost than a blower at high altitude. So the only true way to measure blowers is like some of the fuel teams do-they have a mule motor that turns a blower to measure the boost. I have heard some of them buy 4 or 5 at a time. Run all of them on the fixture-one right after another-all on the same motor. And then keep the one or two that work best and send the rest back. So although boost numbers seem like a great way to measure a blower's efficiency there are more factors in play here. Dave Germain
     
    #2
    Dave Germain, Dec 6, 2009
  3. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    tafc

    on a conventional 526 hemi, a normal psi d at 92 over in tafc trim will make around 42 lbs @ 9000 rpm in high gear, 2500 ft air.

    as said above, roots can make more boost, but it robs a lot more power and puts a warmer air charge out at those higher boost 'pressure' numbers. thus, resulting in less power.
     
    #3
    Will Hanna, Dec 6, 2009
  4. jim phillips

    jim phillips ta/fc

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    that doesnt seem like much i would guess being it takes less horsepower to turn it is why you see more horsepower gain would this be correct
     
    #4
    jim phillips, Dec 6, 2009
  5. AFC357

    AFC357 New Member

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    Ive run em both, YES!
     
    #5
    AFC357, Dec 6, 2009
  6. lambfunnycar

    lambfunnycar New Member

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    What is the psi at 10,000?
     
    #6
    lambfunnycar, Dec 6, 2009
  7. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    10k

    Measuring boost at 10,000 rpm is kind of like measuring your....well, never mind, you get the point...hard to get a 'straight' answer from anyone and who cares if it's right...

    Checking boost at 9000 in high gear is a somewhat standard measurement for a quarter mile car. Since that RPM is usually achieved every run, it's a good place to check your boost. Now this is only truly applicable to the same car, same computer.

    I was told a story by a certain TAFC team. A team going rounds on Sunday at a national thought they were down on boost because their computer 'number' was lower than a few other cars of the same combo at the same track. In an effort to fix the problem, on Sunday, they took a blower off a car that lost on Saturday that was supposedly 3 pounds better than theirs and put it on the car ready to rotate the earth. On the new car, the 3 pound better blower ended up being one pound lower than the blower they had and slowed the car down.

    Lesson learned is boost guages are not calibrated accurately enough to give real good comparisons between cars, no matter what brand of computer. It should only be used as a comparison.

    Usually the best boost guage is the mph on the scoreboard.
     
    #7
    Will Hanna, Dec 6, 2009
  8. bruce mullins

    bruce mullins Top Dragster

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    i quit worrying about what the boost reading showed except to compare run to run to run. as stated above, the heads, cam and intake play a big part of what boost is shown. even the difference from a brad to veney head will show a difference. i even quit worrying about egt's except to look for a problem from run to run. plugs and bearings don't lie. gauges and computers are like cheap women. don't believe them! :eek:
     
    #8
    bruce mullins, Dec 6, 2009
  9. JP

    JP Member

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    Yes , but no matter what they both make us go crazy just by looking at them!!!:D
     
    #9
    JP, Dec 6, 2009
  10. lambfunnycar

    lambfunnycar New Member

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    Who has a deal for a rookie needing a screw blower?
     
    #10
    lambfunnycar, Dec 7, 2009
  11. Stefan Kontos

    Stefan Kontos Member

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    #11
    Stefan Kontos, Dec 7, 2009
  12. T.Smith

    T.Smith Top Dragster

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    As Rahn Tobler once told me "don't fall in love with the boost gauge".
     
    #12
    T.Smith, Dec 7, 2009

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