GPM @ Idle

Discussion in 'PSI Superchargers Tech Questions' started by hirevn, Mar 11, 2022.

  1. hirevn

    hirevn New Member

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    Earlier this winter while purchasing a new injector hat / BV setup, I was told that they don't really bother with leak down percentage anymore but instead focus more on the flow meter data for GPM @ Idle.
    It was suggested for my setup to aim for 1.1-1.2 gpm at idle. I have not started this new combo yet but did leak down the BV anyway to get close and set it at 83%, just curious if using the flow meter data at idle also is another reasonable way to set this up?
    I tend to believe what I was told as this is a very reputable manufacture and these guys do race what they sell so I have no reason to doubt them, just curious if anyone here does it this way as well.
     
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  2. rb0804

    rb0804 Active Member

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    The leak down was always a reference point anyways. The GPM is a more accurate way to measure it. In the end, it’s whatever works for your particular combo.
     
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  3. jay70cuda

    jay70cuda Well-Known Member

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    I've never used a leak down %. I was always taught to look at the flow meter. I run my hemi around .8-.9 gallons with coil on plug. In killer air it needs more to stop the coil surge but I've never had a issue idling
     
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  4. Mike Canter

    Mike Canter Top Dragster
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    Test it coming off idle. You want it to be instantaneous. If it hesitates it is too lean and idle temps too high so increase the flow slightly. If it blubbers and contaminating the oil or the driver eyes are watering then it is too rich. The flows down at that rate are below the specifications of the flow meter but accurate enough to find what flow is needed.
     
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  5. blownapex

    blownapex Member

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    what about 600-700 egt or 700-800 if you want it mean
    70 od im about .6 gpm
    92od im about .75
    128 im about .85gpm
    but thats my c screw combo at 2000 rpm in neutral
    and doesnt milk oil
    ive seen cars a lot higher than mine at idle
    right or wrong thats what ive always done
    calibration may be a factor also or lack of calibration
     
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  6. td3829mk

    td3829mk Member

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    At the end of the day, GPM/leakdown/blade gap/etc, etc, etc. doesn’t matter. Get it to idle right and then take those readings as initial setup so you can set your combo back to that as needed. If I pay close attention to anything at an idle it’s EGTs and head temp.
     
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  7. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Idle GPM is a much more accurate way to get someone started. Too many variables between one guy's 83% leakdown and someone else's.

    You want a target head temp at stage. Thats the goal of your idle flow. If you part throttle leave, you also have to consider stage flow and balance the spool position and idle check to get your idle flow and stage flow right.

    Personally I'm more worried about the head temp I'm after and the tune up on the track than whether or not it's milking the oil or I can get 14 runs on an oil change.

    Hot head, more throttle response, but you have to put more fuel or less timing in it down track to keep from detonating. The warmer, more detonation and generally less consistent race car.

    Cool head, not as zippy down low, but you can run it leaner and more timing down track. Less prone to detonate. More consistent.

    The warmer the head temp, the longer it runs, it will gain head temp, so it will be sensitive to run time. Lets say you are on a bye and have a quick routine, you stage at 175. Next run the guy jacks around with the wheelie bar, purges the nitrous, etc., you go in 185. Next run, the other car does a long burnout, waves at the fans, eats a burger, then checks the bars, etc. You're 30 seconds longer. 195.
    175, 185 and 195 all take different tune ups to get off the line and live down track without detonation.

    Meanwhile a richer combo may be 135 on that first run and only warm up to like 140-145 on a longer deal mentioned above.

    Also first run of the day vs a motor that has a heat soak comes into play on head temp run to run.
     
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  8. hirevn

    hirevn New Member

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    Thanks everyone for all of the feedback, all really good information to help me get better.
     
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