acceleration help

Discussion in 'InsideTopAlcohol.com Tech Questions' started by caseyspradlin, Mar 20, 2019.

  1. caseyspradlin

    caseyspradlin Member

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    see timing map below.

    upload_2019-3-20_22-30-43.png

    see dip in rpm and g meter when converter locks up pulls motor down and quivers tire i assume because wheel speed is building and then drops and tire starts to roll over itself a little.
    upload_2019-3-20_22-32-15.png

    question is to stop the quiver and keep g meter climbing should i change timing map?

    60's are .988 and wheel speed at 1 s is 2800

    top dragster converter car 1471 chevy

    thanks ITA
     
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  2. lucky devil

    lucky devil Member

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    What rear gear do you have ? My own thought is the wheel speed is to slow
     
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  3. Mike Canter

    Mike Canter Top Dragster
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    Are you running any lean outs?
     
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  4. caseyspradlin

    caseyspradlin Member

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    389 gear for 1/4 mile racing.

    Have the ability to pull some fuel with electronic lean out but not currently in use.
     
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  5. jay70cuda

    jay70cuda Active Member

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    Why a 3.89 gear. ? 4 speed?
     
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  6. Mike Canter

    Mike Canter Top Dragster
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    Then maybe try turning on a 40 jet right before to help with acceleration.
     
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  7. rb0804

    rb0804 Active Member

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    What’s the end goal? Consistent back to back runs? Go faster? Quit shaking the tires?
     
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  8. caseyspradlin

    caseyspradlin Member

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    3.89 gear to get motor rpms where I like...shift 7600 cross 7800. 2 speed PG 1.80 low.

    End goal is to stop the quiver. Assume the acceleration dip is causing it??

    Mike-turn the lean out on while on 2-step and leave on for how long? What about turning on again at bottom of high gear? Again for how long? Another question: shifting on rpm is somewhat variable it seems. So would i need to switch to time shifting. If wanted to stay on rpm I think I could use a relay and I believe grid shifter pulse width is adjustable to activate lean out as well??
     
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  9. BEDNAR1320

    BEDNAR1320 Member

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    FWIW Casey, I don't pull any timing till .1-.15 out to get wheel speed.

    You might try to bring more timing back in sooner......looks like about .4 out it wants more power.
     
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  10. sammy christian

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    what Brian said^^^
    hit it with full timing for the first .1(tenth) and then ramp it in faster.
    I bet it will take it all by 1.0sec without a problem.
     
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  11. rb0804

    rb0804 Active Member

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    Last two posts are good advice, then you can play around with rolling the timing up or down after that to suit your needs. There are other ways to accomplish what your trying to do, like blowing a jet open or using a converter dump. Maybe you get a good base timing curve and then play around with opening and closing some jets.
     
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  12. underby6

    underby6 Active Member

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    I tried to PM you, doesn't seem to be available. Is it a "lockup"? Looks like a gear change occurring.
     
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  13. caseyspradlin

    caseyspradlin Member

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    No lock up
     
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  14. td3829mk

    td3829mk Member

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    What tire are you running?
     
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  15. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Long story short it looks like it is spinning out of a dead hook at the hit. You are feeling it hook out of that spin most likely. G-meter is a measure of RATE of acceleration at any given point in time, so you will obviously see dips in it when the tire hooks.

    In my opinion the problem is at the hit. I would start by moving that -8 first point out to .1 or so and see if that cleans it up. The divot in the wheelspeed curve is the root of the problem. It's wadding the tire up then spinning out of it on the recoil. Get the sidewall right and you can get after it more. Keep moving the point further out until it gets rid of the divot.

    Remember there's still a slight delay in what you program until you see results. If you had a timing optic monitoring real timing, your dip wouldn't happen until like .03-.04.

    Getting some power to it in front of that point is definitely an easier option to try, but it doesn't fix the root problem in my opinion. It may take more testing to get the hit just right. Also just right on a tight track may be different than just right on a hot track.
     
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  16. Bjs344

    Bjs344 Member

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    Not sure I understand? With his current timing curve, the timing is out while he’s on the brake.

    But I think you’re saying that after he puts the first dot at 0 retard then the grid has a .030 latency vs the programmed curve? Is that a known limitation of the grid? Is the latency the same no matter how far you are from brake release?

    I could see if you put a dot at .001 after brake release that there could be some latency, but I would expect it to be at the third decimal and that anything after .01 would have 0 latency.
     
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  17. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    The first dot is at 0.0 and is 0 degrees retard.

    It really opened my eyes first time I got on a car with an optic recording timing and saw the delay in the programmed 'bottom' of the curve right after the hit and the realized bottom.

    I think part of that delay is due to only having 4 magnets on the degree wheel. You really can't see a good picture of wheelspeed at the hit with a 4 magnet collar, so it makes sense there's not enough 'resolution' to have a faster reacting timing curve.
     
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  18. BEDNAR1320

    BEDNAR1320 Member

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    Will, have you considered that the pinion is rotating much, much slower than the crankshaft at the hit and shorty thereafter? I'm not arguing your point about the timing delay because you would know from experience. Just thinking the crankshaft speed would make for an accurate resolution compared to the driveshaft.
     
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  19. BEDNAR1320

    BEDNAR1320 Member

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    While I'm thinking about it, do you have any idea why I have to static set my crank trigger pick about 6-8° before the point I want my timing? RCD hub and the long skinny pick up, MSD 8+ with the Grid.
     
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  20. Bjs344

    Bjs344 Member

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    If I’m on the chip at 4000 rpm, the next spark plug will fire less than .003 after button release. As the motor accelerates, this time goes down. There should be no reason (other than crappy design) that the grid can’t fire that cylinder at the prescribed timing for .003 into the run. Feel free to check my math on the .003 number, I haven’t had my coffe yet this morning.

    I’m not doubting Wills experience, just saying that if there really is measurable delay these are the possibilities I can think of.

    1. MSD cheaped out on either the design or construction


    2. The instrumentation Will was looking is inducing a time shift in the recorded firing pulse

    3. the grid data and racepak data are not properly time aligned for one or more reasons
     
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