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.

back when i was looking at them i thought they needed 12-12.5 volts to run. things may have changed since then but at that time they needed more voltage than an inductive system.

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.

Doesn't the small red wire only connect the large red wire to the box when it sees voltage? Otherwise the box would be hot every minute of every day, connected directly to the battery.
I don't think it's any more complicated than that. Crank or run, it needs to see voltage for the box to work. And if you have 12VDC in the large wire, why would you have any less in the small wire?
R.

""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.

MSD's do NOT like less than 12 volts!

My car started running poorly the minute my alternator quit working.

I'm running MSD with the battery in the trunk. I've never measured voltage while cranking but its probably down around 7 or 8 volts like most cars. No problems starting. Agree MSD's don't like low voltage for sustained running but mine handles starting fine.

I run a MSD 6AL and if it will crank, it will fire. I've had it start with 10V showing on the gauge. The digital boxes are another story - they seem to need 12V minimum to fire.

"" 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.

Did you ever get a response for the minimum crank voltage? I just installed an MSD 6AL2, and it is dead- no spark. My batt voltage is 12 but my voltage to the little red wire, after it goes through the ignition switch is 10.5. I have no power to the coil

I never got a response on the MSD tech board.

EDIT:
http://www.msdignition.com/forum/showthread.php?p=74027#post74027

I just added another BUMP post to my thread and I added the 6AL2 box too.

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.

I am having the same problem with my new 6AL. car won't start unless I jump it. I have Batt. in trunk. I have 9.5v cranking. called MSD tech they said my Voltage is to low. sheet that came with box says it will work from 9 to 16 v. So Tech support and instructions don't agree. in the mean time I am stuck with a sick Cuda. they should say it takes two batt. to run their sys. I am thinking about sending it all back and try somebody else's sys.

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

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.

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

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.

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