How to shift on rpm?

Discussion in 'InsideTopAlcohol.com Tech Questions' started by racecar1517, Jan 8, 2020.

  1. racecar1517

    racecar1517 Member

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    The goal is to shift twice at the same rpm. The car is uses a grid, and a b&j. The grid supplies 1 programmable output signal that can be used for (anything) shifting. That programmable out will be triggered every time the rpm reaches the set point.
    If the two air solenoids are both wired to the same output, the car would shift both gear sections at the same time skipping 2nd gear. So how does one separate the two shifts.
    The second question is how do you keep the air pressure constant when the signal is removed after the shift. The he signal that comes from the grid is just supplied when the rpm is above the set point. When the shift takes place, the rpm would drop below the set point, power is then removed from the output of the grid, and it would vent the solenoid and the transmission goes into neutral.
     
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  2. greenracing

    greenracing Member

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    Caveat - I'm putting mine together too and haven't done this yet, but this is the plan based on my conversations with others :)

    Use the time/RPM output (brown/white wire) for the first shift.
    Use the shift light output (yellow wire) for the second shift.

    I'm using Electrimotion shift solenoids. They have separate shift and dump solenoids, so the pulse output from the grid will trigger the shift and the solenoid will hold the air pressure. I have a 'dump' button to trigger the dump solenoids.

    If you're using a solenoid that needs to remain powered you'll have to wire up a latching relay circuit to hold power on the solenoid after the grid pulse. Your dump button will break the latch.

    That's why I went with the Electrimotion solenoid - much simpler wiring because they are 'self latching'. Plus I trust them to handle the 400 PSI shift pressure.
     
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  3. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    For a three speed application, I would recommend adding the 3 stage timer, MSD pn 7760. You will have to add it to the MSD 7740 Can Bus extension if you don't already have one. You will need to use relays, so I recommend the MSD 4 stage solid state relay MSD 7564.

    This is how I was going to shift my 3 speed in my FC/Altered.

    The 3 stage timer can work off time, rpm or time and rpm. It will have the same ground output the brown/white wire has. The three stage timer can't support the load of a solenoid, so you have to run the circuit through a relay. The MSD unit is a nice solid state deal, so it will be more reliable than a mechanical relay. I was going to wire mine to apply 12v out of the relay, so you would wire the other side of your shift solenoids to ground.

    You will want to be able to upshift for the burnout manually, so I was going to use two toggle switches putting 12v to the solenoids. It's not a bad idea to wire a light to this circuit or have some way to make sure you get these solenoids reset every time to insure you are in low gear.

    If you are in a car you want to be able to dump into low gear in the shutdown area, and be able to drive off the track, I was going to wire the ground side of my solenoids through another switch. This would allow me to dump into low gear without killing ignition. I would not want to rely on an 'off time' in the timer because you want to get it dumped into low pretty quick in shutdown so you're not engine braking on decel. If your normal procedure is to kill ignition in shutdown, you may not need the dump switch. The Top Dragster I am wiring kills power on the chute button (using Leahy safety shutoff), so it's not necessary.

    If you want something plug and play, I would recommend an ACD unit.
     
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  4. racecar1517

    racecar1517 Member

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    Will,
    Thanks for your input. I like that it uses the grid. And the need for the pre and post race functions.
    I'm curious what solenoids were you thinking.
     
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  5. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    Todd Tutterow sells the combo flow valves for both B&J and Lenco. They are basically an "air relay." So the solenoid is a small low pressure electric over air that doesn't draw much. On the transmission side, the low pressure signal activates the valve, which has your high pressure plumbed in. The valve replaces the top plate on a Lenco pod, and you can either mount direct to a B&J through the 1/8 NPT port or mount remotely. The signal solenoid does need to be close to the transmission since the signal line is only 5/32.

    Call Brad Schmidt, who works for Tutterow, 980-429-0523
     
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  6. greenracing

    greenracing Member

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    Hey Will,

    Thanks for pointing out the solid state solenoid - that will make wiring pretty nice and be a bit more reliable.

    Do you see any reason not to use the brn/wht and yellow outputs on the Grid? I'm not using them for anything else so adding the 3-stage may be unnecessary expansion. The only drawback that I see is that the 2-3 shift is by RPM only, so you lose the time window feature. My only other concern is keeping the yellow output on long enough to get the shift cylinder to full pressure.
     
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  7. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    The schematic you drew up with the brown/white timer wire and the yellow shift light wire will work with the latched relay you described. I don't believe you will be able to use the MSD Solid State relay for the latched circuit. It only has + outputs. Since you will have a ground output from the yellow shift light wire, you need your output signal to be the same as your trigger signal so you can latch them. A conventional solid state relay should be able to do this since you can choose +/- output.

    I wouldn't trust a mechanical relay on this circuit, because if it fails, it downshifts.

    If someone is going to use the brown/white output switch and the yellow shift light wire from the grid to shift, I would recommend the Leahy shift solenoid set up since you won't have to rely on a relay to keep your shift solenoid latched.

    If this is going in a dial in car like TD or TS, I personally like shifting on time instead of rpm. Blown converter cars tend to not be real sensitive to shift rpm as they are time.

    One TD racer told me he had his set up to shift with both time and rpm, both hooked to different shift lights on the dash. If the rpm light came on first, he knew it was fast. If the time light came on first, he knew it was slow. If they both came on at the same time, he was where he needed to be.

    I'd love to do that on the Kruse Missile, but we shift into high at .8 to 1.0 to slow it down to 6.10
     
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  8. greenracing

    greenracing Member

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    Thanks Will.
    I've got the Leahy solenoid, so I won't need to have a latching relay circuit.
     
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