fuel converter tune up

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by caseyspradlin, May 15, 2018.

  1. caseyspradlin

    caseyspradlin Member

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    I have been seeing the below hump in low gear rpm graph for years and just thought it was the converter doing it's thing when the transbrake releases. Tried a different manufactures converter and it was more pronounced. Starting to think its fuel curve related. Thoughts? What can I do about it?

    509 BBC big chief littlefield 1471 HHR Powerglide. K valve erderle hat 110 pump. single high speed bypass

    [​IMG]IMG_2963 by CASEY SPRADLIN, on Flickr
    above new converter

    [​IMG]IMG_2962 by CASEY SPRADLIN, on Flickr
    above converter been using for years

    Thanks ITA!
     
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  2. Bjs344

    Bjs344 Member

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    Open a leanout.

    Mine does something similar. I talked to my converter guy and I was falling back higher than him after the shift but flashing a lot lower than him in low gear. And he's centrifugal so you would think he probably has less boost off the brake. That's what convinced me to try a low gear timed leanout and it definitely makes it sportier down low and it raises and smooths out the flash portion of the erpm.
     
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  3. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Simple answer is the driveshaft is catching up to the 'lock up' of the converter. If you clicked the engine to d/s on your racepak, you would see the line go flat there. So let's say your converter averages around 15% slip at this point. So if you had a 1.80 low gear, your engine to d/s would read 1.95ish.

    Fuel curve will only make one of two things happen given the same converter. If the converter does not slip more with the extra hp, it will result in more wheel speed. If the converter does not stay coupled, it will flare the converter harder and have a more pronounced pull back at the point the driveshaft catches up with the converter. If the engine doesn't pull back, the driveshaft will 'pull up' aka tire shake.

    All of that aside looking at the Racepak graph, you could stand to hit it a little harder on the hit. It doesn't look like it is quite to the point of driving over the tire, but it looks to be stuck pretty good. That definitely has something to do with the flare in engine rpm early.
     
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  4. Bjs344

    Bjs344 Member

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    When mine rolled over it would correspond to falling off the tire (evidenced by high frame rate video with good timestamp display). I could put the timing back in vertical but it would still fall off and roll over.... or rollover and fall off, never was sure. Either way the leanout kept it up on the tire and smoothed out the rollover.
     
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  5. sammy christian

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    Will is dead on, I see the same if you "underpower" it.
    If you are happy with how it runs, leave it alone and ignore that.
    If you are trying to go a little faster, you definitely need to put some power in it at the release and apply some quicker. More wheelspeed sooner.
    Those graphs look nice for a super stock car with a dead hooked 14x32/305ci combo.
     
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  6. BEDNAR1320

    BEDNAR1320 Member

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    How much timing are you pulling?
     
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  7. caseyspradlin

    caseyspradlin Member

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    thanks everyone, that helps explain it. I am pulling 10 deg out for 1 sec. in a deliberate attempt to have 1.0 60's as I feel that will be the most consistent over a broad range of track conditions.
     
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