MSD Minimum Cranking Supply Voltage
#1196837
03/14/12 11:05 AM
03/14/12 11:05 AM
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Joined: Jan 2003
Posts: 5,443 Indiana
YO7_A66
OP
master
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OP
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Joined: Jan 2003
Posts: 5,443
Indiana
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What is the lowest cranking supply voltage that you can get away with when using a MSD box?
I have asked the MSD techs and they have not given me an answer in two days, so I thought that I would ask the real experts.
I have only found one place on the web that mentions 10.5v, one mentions 9-12v, and another one says 10v is the lowest cranking supply voltage, so I want to make sure. Thanks to all.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: MSD Minimum Cranking Supply Voltage
[Re: lewtot184]
#1196839
03/14/12 01:56 PM
03/14/12 01:56 PM
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Joined: Jan 2003
Posts: 5,443 Indiana
YO7_A66
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I believe that there is a different voltage required for the (RUN/CRANK) SMALL RED WIRE versus the LARGE RED WIRE. I am pretty sure that the LRW has to have a minimum of 12v when the SRW has voltage going thru it. I should have clarified but I am asking about the SRW minimum voltage for CRANK.
Then I believe that there "might" be a difference in voltages between the boxes (-5,-6,-7 etc.) too.
Thanks for the reply.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: MSD Minimum Cranking Supply Voltage
[Re: dogdays]
#1196841
03/15/12 11:46 AM
03/15/12 11:46 AM
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Posts: 5,443 Indiana
YO7_A66
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""Doesn't the small red wire only connect the large red wire to the box when it sees voltage?""
That is correct.
""And if you have 12VDC in the large wire, why would you have any less in the small wire?""
The large wire is wired directly to the battery post. The small wire has the CRANK and RUN wires which both have several connectors along their length. The RUN wire has these connectors plus it also feeds 2-3 other items. All of these connections equal voltage drops and the small red wire will never see 12v at CRANK due to all of these drops. All of these drops are why I am trying to figure out what the minimum voltage needs to be to make the MSD box happy during the CRANK mode. The RUN voltage will see apx 14 volts all the time, but the CRANK voltage depends on the voltage drops and the condition of the battery each time you start it up.
From what I have tested, I think that the minimum is around 10.5v to be safe. My car was showing 10.1v during CRANK and it would not start, three different times. Then I showed a 10.2v reading and it started. Then I ran the CRANK ignition wire directly off of the ignition switch straight to the MSD small red wire and now I am reading 11.1v during CRANK and it starts immediately.
Note: The 10.1v/10.2v/11.1v readings were taken when the battery was about 85-90% charged. Thank you for your response. Note: Three days now and MSD has not responded.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: MSD Minimum Cranking Supply Voltage
[Re: YO7_A66]
#1196842
03/15/12 09:25 PM
03/15/12 09:25 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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MSD's do NOT like less than 12 volts!
My car started running poorly the minute my alternator quit working.
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Re: MSD Minimum Cranking Supply Voltage
[Re: Evil Spirit]
#1196845
03/16/12 08:58 AM
03/16/12 08:58 AM
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Joined: Jan 2003
Posts: 5,443 Indiana
YO7_A66
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"" I run a MSD 6AL and if it will crank, it will fire."" Since I rewired my CRANK circuit, I am very impressed how quickly the engine will fire with the MSD Street Fire (MSD-5) box. Now, once I turn the key to CRANK, it fires so quickly it is hard to read the voltage output on my digital voltmeter for the CRANK circuit before it starts reading the RUN circuit. It can't be any longer than one second before the engine now fires. Once I get an official response from MSD tech line, I will update this thread with their minimum CRANK voltage requirements.
Thanks again.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: MSD Minimum Cranking Supply Voltage
[Re: YO7_A66]
#1196848
04/10/12 12:29 PM
04/10/12 12:29 PM
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Joined: Jan 2003
Posts: 5,443 Indiana
YO7_A66
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A tech responded after the bump this morning: ""just like our other boxes you need a minimum of 9V's while cranking for the unit to be happy"" http://www.msdignition.com/forum/showthread.php?t=17745 Thanks for asking. It reminded me to bump the MSD thread.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: MSD Minimum Cranking Supply Voltage
[Re: 65cuda]
#1196850
07/25/14 04:03 PM
07/25/14 04:03 PM
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Joined: Jan 2003
Posts: 21,073 Niles , Ohio
therocks
oh wait.but hey.lets see.oh yeah.
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oh wait.but hey.lets see.oh yeah.
Joined: Jan 2003
Posts: 21,073
Niles , Ohio
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If you have only 9.5 volts cranking you have a problem.Either the battery is weak or too small.Or cables too small or poor grounds.That or starter is drawing too much.You should have at least 10.6 cranking.Dont blame MSD for another problem.My 440 with 12.5 compression usually stays at 11.5 volts or so cranking.Rocky
Chrysler Firepower
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Re: MSD Minimum Cranking Supply Voltage
[Re: therocks]
#1196851
07/27/14 04:40 PM
07/27/14 04:40 PM
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Joined: Feb 2003
Posts: 515 Dayton, Ohio
65cuda
mopar addict
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mopar addict
Joined: Feb 2003
Posts: 515
Dayton, Ohio
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Ok I took the batt. out and had it tested. its a 1000 cca. they said it was 100% good. I took the old starter out and put the new style small one in. it spins it fast and you can hardly hear the starter now. still the same problem. 9.6v cranking. it try's to hit but wont start. put a jump box or a charger on it and it starts right up. I can't believe you can crank that much motor and only lose 1 volt. how close is your batt. to the motor.
65 Cuda 360,3.23 SG-13.97 @99.4, 88 D100, 2000 Kota Qcab, 71 Duster 416 11.84 @110., 73 Imp ,(2)72 & (1)71 Dart Swingers GarysMocars Legendary Dealer
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Re: MSD Minimum Cranking Supply Voltage
[Re: 65cuda]
#1196852
07/27/14 05:41 PM
07/27/14 05:41 PM
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Joined: Jan 2003
Posts: 21,073 Niles , Ohio
therocks
oh wait.but hey.lets see.oh yeah.
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oh wait.but hey.lets see.oh yeah.
Joined: Jan 2003
Posts: 21,073
Niles , Ohio
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Mine is still OE.I do run 1 gauge cables even though they are under hood.On trunk installs I run either 0 gauge or 1 gauge.Did they load test the battery where it actually puts a load on it?The stores usually use the small hand testers.I never used them even at work because you can have a battery drop when its loaded with a big tester.We had a 400 buck SnapOn small one and it just sat and collected dust.Rocky
Chrysler Firepower
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Re: MSD Minimum Cranking Supply Voltage
[Re: therocks]
#1196853
07/27/14 06:08 PM
07/27/14 06:08 PM
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Joined: Feb 2003
Posts: 515 Dayton, Ohio
65cuda
mopar addict
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mopar addict
Joined: Feb 2003
Posts: 515
Dayton, Ohio
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AZ had a hand held tester. I looked at it to see if it has a resistor network and it did under a vented metal cover. I also put a new 800cca batt. in it and same thing. I used some cable I got from work years ago. not sure what gage it is. it is as big as most batt cables I have seen. I will have to look again and see what gage they are. worked with the old chrome bx for 8 years. don't know why the MSD has to be so picky.
65 Cuda 360,3.23 SG-13.97 @99.4, 88 D100, 2000 Kota Qcab, 71 Duster 416 11.84 @110., 73 Imp ,(2)72 & (1)71 Dart Swingers GarysMocars Legendary Dealer
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Re: MSD Minimum Cranking Supply Voltage
[Re: 65cuda]
#1196854
07/27/14 10:35 PM
07/27/14 10:35 PM
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Joined: Jan 2003
Posts: 21,073 Niles , Ohio
therocks
oh wait.but hey.lets see.oh yeah.
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oh wait.but hey.lets see.oh yeah.
Joined: Jan 2003
Posts: 21,073
Niles , Ohio
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Ill bet that cable is either too small or has corrosion inside or both.The ends can be clean but under the insulation it gets the green death.Most factory batt cables were 4 gauge.Too thin to run from rear to front.Rocky
Chrysler Firepower
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