Adjusting Tune for bad air.

Discussion in 'PSI Superchargers Tech Questions' started by ltcunningham, Jul 28, 2014.

  1. ltcunningham

    ltcunningham New Member

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    Hoping to see how you guys adjust for bad air. We run a 565" BBC with a 14-71 blower. Weather this past weekend had us struggling. We run a 4.89 index class and normally have to make adjustments to slow the car down.

    Temp was 92. Heat index 104.
    Water grains 152.
    Humidity 75%
    Baro 29.5

    We tried changing pulleys and fattening her up a bit. But wasn't helping. Is there a correlation to the high water grains and the car not picking up like it should? Really left us scratching are heads.

    Thanks in advance.
     
    #1
    ltcunningham, Jul 28, 2014
  2. Torment

    Torment Member

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    My program is a little different than most around here with a smallish screwcharger (18-24psi range) and ethanol... but on a hot day with high humidity I'm leaning up the fuel first, maybe adding a degree second. A pulley change could also do it, but I usually determine what OD I'm running for the day before I even leave for the track... so for me it's about honing in that OD on any given day.

    Interested in what some of the sharper guys here do as well...
     
    #2
    Torment, Jul 28, 2014
  3. Randy G.

    Randy G. Top Alcohol

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    If you have clearance, head gaskets.
     
    #3
    Randy G., Jul 28, 2014
  4. Mike Canter

    Mike Canter Top Dragster
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    There is more to the weather picture than you think. First of all the Density Altitude is 3641 ft. Time for a transmission gear change to bring the power back because it is going to be a pig on launch at that DA. The water grains are really 162 which is even worse. Not much you can do about that other than what Randy suggested in changing the head gasket. Not sure about your method of selecting a main jet by humidity only. It is correctly done by computing the Density Altitude. If your motor is jetted for 3000 ft and it drops to 1000 ft then your method is going to take out a piston and goes for the other way around if you are jetted for 1000 ft and it goes to 3000 ft then it will be a fat pig with the wrong gear ratio in need of higher compression.
     
    #4
    Mike Canter, Jul 29, 2014
  5. JimW

    JimW Member

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    We mainly run a 4.70 class racing.
    Speed up and slow the car down with launch RPM and timing with a MSD Grid.

    Couple of weeks ago we ran a 4.702
    I tell people, we might not be able to do it again but, we didn't do it by mistake.....

    Jim
     
    #5
    JimW, Jul 31, 2014
  6. ltcunningham

    ltcunningham New Member

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    We haven't tried using launch rpm. We have been trying timing. We were retarding the motor about 2 seconds into the run. Next weekend we are going to try taking time away at the start of the pass.

    I really appreciate the response. We don't run like the pro mod guys do, but it is interesting reading how they make adjustments.

    Canter, Hanna keep it coming.
     
    #6
    ltcunningham, Aug 1, 2014

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