Tunning questions

Discussion in 'PSI Superchargers Tech Questions' started by gregl, Oct 27, 2006.

  1. gregl

    gregl Member

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    Hi everybody this is a cool site.I race a pro mod blown alcohol hydro drag boat.I have done pretty well with the use of davenport fuel management software.My concern is overnight i seem to lose my tune-up.This is a seven second class.On saturday qualifying I get three passes to get it figured out.Some weekends it stays the same for the next day and some it changes 2 or 3 tenths overnight.I use actual altitude,temp,humidity,and my program gives corrected altitude.Is water grains what i need to measure to stay consistant?Are water grains and humidity all that different?Any help would be great.
     
    #1
    gregl, Oct 27, 2006
  2. T.A.D. 776

    T.A.D. 776 New Member

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    Dose it seem to get leaner overnight ?
    Methanol absorbs 10 times it's weight in water from ambient air plus condensation problems added to it.
    Moisture absorption in the fuel is a major problem in alcohol powered boats and race cars in high humidity environments.
    To keep the fuel from getting wet we put a shut off valve on the tank vent before that it was Saran plastic wrap. Anywhere air touches your fuel so does moisture.
    Check the specific gravity of your fuel after letting the boat sit overnight.
    It's usually the simple stuff.
     
    #2
    T.A.D. 776, Oct 27, 2006
  3. Mike Canter

    Mike Canter Top Dragster
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    The only time Water Grains should have a bearing on the tuneup is if the Davenport software reads out that it is over a 100 grains. There is not much you can do if it is over 100 grains. Remember it will be over 100 grains for everyone else also so they should slow down the same. Is everyone else changing in performance also?
     
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    Mike Canter, Oct 27, 2006
  4. gregl

    gregl Member

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    That is a good point about the water in the fuel.We do usually fill it up at night so everything is ready and we can drink beer.haha
    It does seem the changes are among most of us,but there are a couple af teams that can run .00s every pass.They tel me they are doing the same stuff I am but I am not beliving them.
    It is very hard to see any kind of pattern.Somedays it will be a little faster than I think and somedays it will be slower and most of the time it stays the same.Do most of you guys run down the track at exactly the same engine temp. every time.I don't have control over how long it takes me to get in the water and then how long I sit on the rope waiting to go.
     
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    gregl, Oct 27, 2006
  5. Mike Canter

    Mike Canter Top Dragster
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    It is pretty routine on starting the motor doing a burnout backing up then staging. There are some things that can cause slight delays but not that much.

    Do you record the Water Grains to see if there is any correlation? The Density altitude should change a lot depending on the time of day or night and that will change the performance.

    How do you know that your tuneup is right on? If it was off by always to rich or too lean it would result in more change if the weather changes. Are you adjusting the Davenport Jetsize "Tuning Modifier" by your plug readings to get it to match?
     
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    Mike Canter, Oct 27, 2006
  6. eli

    eli Banned

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    Fill the tank up ??? you should be draining the tank over night, Helloooo, you race in WATER!! it don`t get any wetter than that:rolleyes: ;)
     
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    eli, Oct 27, 2006
  7. gregl

    gregl Member

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    How do you set your flow modifier by the sparkplugs?I get within a tenth and then adjust it according to what it needs to be.For instance if I run a 7.10 and my flow mod is 100.I will adjust the flow mod to give me ten jets leaner which in theary should be a 7.00.My spark plugs always look almost new.Everybody that looks at them says not to change a thing.
     
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    gregl, Oct 27, 2006
  8. Mike Canter

    Mike Canter Top Dragster
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    My recommendation is to first read this article on Blown Alcohol plug reading http://www.dragstuff.com/techarticles/reading-alcohol-spark-plugs.html.

    Then after a run you read the plugs and if the motor looks like it was running rich because of no color (frosting) on the metal thread base then you can raise the Tuning Modifier (TM) number which will lean out the system. When you raise the TM watch the GPM in the window on the left change accordingly. So you can raise the TM and have it pull out .2GPM or whatever you want. Or you can lower the TM (even into he negative range) to richen the system. The idea is to calibrate the Jetsize software to your motor's fuel system and to the observed weather. Once you get the TM adjusted then you leave it alone unless you change the pump or something major like that then you will have to re-calibrate it. If your fuel pump is weraing out then you will have to keep changing the TM to keep up with the pump. If you keep changing the TM everytime you read the weather I believe you will chase your tail and be inconsistant and this could be the cause of your problem.

    Has you fuel system been flowed?
     
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    Mike Canter, Oct 27, 2006
  9. JP

    JP Member

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    Did I undertand you correctly ?
    The tuning modifier is not even close to change your ET (7.10 to 7flat by ten sizes) what it changes is your actual fuel flow TO THE ENGINE.

    To get your thoughts right and so you can undertand how it works LEAVE your TM the same all race and follow the suggeted jet size as the weather changes. Example at night good weather with a (-100 example) TM your main jet is 80 then in the hot day with the same tm (-100) your sugested size jet is 85 , so if you want the same engine egt ect use the suggested size if you want it leaner then go extra five (90) .

    hope this helps!
     
    #9
    JP, Oct 27, 2006

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