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Voltage drop at shift vs consistency
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DRR Sportsman
Picture of Stephen Hughes
posted
So last time out I loaded my car the night before. Rolled to the track on Saturday and unloaded. When it was time to fire the car and warm it up, I got nothing but clicks out of my 16v battery. So I go into make it work mode and I steal battery out of my trailer, which is a beotch to get out, and of course it wont fit. So since i’m not going to go down the track with a ratchet strap holding my battery, i zip down to the o’reilly and pick up an optima. Unhook my 16v alternator and go about my day. Car had been killer all season but with the 12v and no alternator it flat sucked and had most of it’s swing in the 60-330. After downloading runs from grid voltage was dropping from 12.1 to 11.2-11.4 at the shift point (dixie electric solenoid). What voltage in real life is too low? MFI on alky set up pretty fat. Msd instructions claim down to 10 volts but i’m nearly convinced at this point that the voltage drop was the issue. Anybody else seen anything similar?


The Pull-Out....for when you want to work smarter, not harder!!!
 
Posts: 336 | Location: Texas | Registered: September 12, 2005Reply With QuoteReport This Post
DRR Pro
Picture of rusty
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were you at pine valley?from what ive seen that drop would not affect consistency,of course there are always other variables.mabe coil weak ect.at pine valley from what i am hearing it could easily be the track.i am assuming your voltage drop is momentary at shift.i always used air until the car i have now.now i tell it to shift then drop volts back out quickly


honesty is the best policy,insanity is a better deffense
1.036, 6.16@ 224

 
Posts: 1404 | Location: texas | Registered: February 17, 2006Reply With QuoteReport This Post
DRR Sportsman
Picture of Stephen Hughes
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quote:
Originally posted by rusty:
were you at pine valley?from what ive seen that drop would not affect consistency,of course there are always other variables.mabe coil weak ect.at pine valley from what i am hearing it could easily be the track.i am assuming your voltage drop is momentary at shift.i always used air until the car i have now.now i tell it to shift then drop volts back out quickly


No sir this was HRP’s last race weekend, been about a month but I was just going over the data. I’ve used this shift set up since the car was new in 03, but it’s had an alternator since day 1 and even with alternator there is a voltage drop momentarily at the shift, but of course with alternator that voltage starts out higher and doesnt drop near as low. It’s all fixed back like it is supposed to be so I guess we’ll find out next time if that was the issue or if I need to start looking elsewhere.


The Pull-Out....for when you want to work smarter, not harder!!!
 
Posts: 336 | Location: Texas | Registered: September 12, 2005Reply With QuoteReport This Post
DRR Sportsman
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My dragster started out with a non spring type electric shifter and no alternator. When I installed my racepak I found the shift was moving around and a big voltage drop. Shortly after I added an alternator and the shift is dead on now.


Denis LeBlanc

 
Posts: 465 | Location: Manchester, NH | Registered: February 03, 2006Reply With QuoteReport This Post
DRR Pro
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The 7730 / 7720 Ignitions will deliver full voltage with a supply of 10 - 18 volts and will operate with a supply voltage as low as five volts.

The 1 volt drop when activating a large electric shift coil is normal in all MSD Re-View files that I have looked at. I’ve seen larger voltage drops with nitrous coils in some Re-Views.

I’ll write this opinion again about what I believe should be used in 7730 Grid to shift your transmission using RPM. The MOST accurate Grid 7730 feature for shifting on RPM is the Shift Light feature. The Output Switch RPM feature is not as accurate as Shift Light in the many MSD Re-View DA files that I have examined.

Add on Grid Modules like the MSD 7760 3 Stage Delay Timer should not be used as a primary shifting activating device. In my car I use the 7760 to activate the Trans Brake solenoid lock out for both No-Box and Box, my Hail Mary shift activation and other things I chose to activate during a run. These events are not dependent on the most accurate activation with either RPM, Time or both together.

When MSD Grid channels are shared with RacePak, I believe the period of time for the shared event could be skewed slightly.
 
Posts: 2450 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Sportsman
Picture of Stephen Hughes
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What is it that makes the output switch not as accurate as the shift light output? Mine is and has been on the output switch and I have noticed some variations in the time that the shift occurs, but I have always contributed that to changes in weather etc making the car actually get to the shift rpm quicker or later. The actual time only varies about .04-.05.

Off the subject a little but with K&R wiring set up and grid, to switch to time shifting would I just change it in msd view and set the time there, or leave it alone and move the jumper on the k&r board and set the time in the delay box timer.


The Pull-Out....for when you want to work smarter, not harder!!!
 
Posts: 336 | Location: Texas | Registered: September 12, 2005Reply With QuoteReport This Post
DRR Pro
Picture of rusty
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01, 2019 12:30 PM Hide Post
What is it that makes the output switch not as accurate as the shift light output? Mine is and has been on the output switch and I have noticed some variations in the time that the shift occurs, but I have always contributed that to changes in weather etc making the car actually get to the shift rpm quicker or later. The actual time only varies about .04-.05
I see the difference and have also contributed to the.track and weather.i use a digital 7 to operate mine


honesty is the best policy,insanity is a better deffense
1.036, 6.16@ 224

 
Posts: 1404 | Location: texas | Registered: February 17, 2006Reply With QuoteReport This Post



DRR Pro
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quote:
Originally posted by Stephen Hughes:
What is it that makes the output switch not as accurate as the shift light output? Mine is and has been on the output switch and I have noticed some variations in the time that the shift occurs, but I have always contributed that to changes in weather etc making the car actually get to the shift rpm quicker or later. The actual time only varies about .04-.05.

Off the subject a little but with K&R wiring set up and grid, to switch to time shifting would I just change it in msd view and set the time there, or leave it alone and move the jumper on the k&r board and set the time in the delay box timer.


The main task of 7730 Grid is timing. For every timing input signal, Grid analyses all the programmed retards to determine when the output firing pulse will be triggered. All the other programmable tasks are less priority. The priority level of each task in Grid will determine how accurate these settings will be carried out.

By using the Launch channel to zero the Data Acquisition I have come to these conclusions of my Re-Views.

Given the rate of engine rpm acceleration, I believe the Grid Shift Light RPM feature has shown to be the most accurate for activating at the programmed RPM setting in the many MSD RE-View DA that I have viewed. By this, I mean within several (less than 5) rpm of the programmed Shift Light setting.

In the Grid Output Switch functions ( Time and RPM ) I find the Time feature to be less than 0.005 in error from programmed time. But I have seen the RPM feature to be in error +/- 10 rpm or more.

To determine the actual shift RPM activation when using the Output Switch I suggest doing this.

In Re-View open the RPM and Launch channels and zero the run to Launch. Now open the Output Switch Channel and expand the view to the maximum display. Place the cursor directly on the Output Switch going High and look at the RPM in this position. If you do this to at least 20 runs you’ll get a good idea of how accurate your programmed shift rpm setting is being activated in Output Switch.

For me, I want the Shift RPM or Shift Time to be as accurate as possible. I also want to be able to make the choice of using either rpm or time or both together using Grid. I have 4 activation wires from Grid attached to the air shifter output solenoid in my car to allow all the different options that I use to shift with.
 
Posts: 2450 | Location: 53056 | Registered: December 30, 2009Reply With QuoteReport This Post
DRR Sportsman
Picture of Quick Dawg
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I totally concur that the output switch isn’t accurate as other sources. I used it for awhile and noticed inconsistencies. Tried both shifting on time from the box (K&R) and with a Digital Delay rpm shifter as comparisons, and they were both very consistence and accurate, the Grid wasn’t. My method of monitoring was using one of the step wires (pink) to monitor the 12 volt event of applying power to the shift solenoid vs. rpm time line.
 
Posts: 166 | Location: Salt Lake City | Registered: January 16, 2012Reply With QuoteReport This Post
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