msd 7531 with nitrous

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raffaplymouth
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msd 7531 with nitrous

#1 Post by raffaplymouth » Tue Nov 03, 2015 3:03 am

hi guys , i have recently buy and installed a 7531 and crank trigger for my Cuda , instead of 6al box and timing control + mechanical advance distributor , nitrous was applied in 2nd after .02 with delay box

i want a advance curve in 1nd gear ( 20 at idle and 38 total ) , and when put in 2nd gear ( nitrous applied ) another curve with 8 degree retarded

i have some question :

1) how to make the same advance curve that i like with 7531 box ? i have started the car and with no positive applied at any wires step, i see when you select the gear 2 thei receipt the signal maked in gear 2 plot curve ... this is correct ???

therefore need make another curve more advanced in the gear 1 when positive is applied on pink wire ??? and when will put 2nd ( no positive applied) that will retard of 8 degree ??

im little confused of which way is better and sorry for my english , i think is better with no positive apply in 1nd and when put 2nd and nitrous have positive apply but i dont know if can work ... Help me !!
1970 Super Cuda 496 Indyheads
ET 9.32@148 1.42 60ft (250 shot ) :shock:

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Re: msd 7531 with nitrous

#2 Post by John_Heard » Tue Nov 03, 2015 8:02 am

First of all you need to realized you've got a ignition box designed for drag racing primarily, it times all of it's functions off of the launch signal.

#1 Wire up your nitrous to one of the Step retard inputs, that way it doesn't matter what gear you're in when you turn the nitrous on, the correct retard will be applied. It's not a good idea to try and do that with a gear retard. The step retard function is what you want to use for the nitrous.

#2 You'll have to rig up something in order to apply a retard at idle to XXXX RPM, what specifically do you want this "Advance Curve to do? You might be able to use the RPM switch and connect it to one of the step inputs to apply a retard below a certain RPM. You'd probably have to add a relay to do this as the step inputs require a positive input, the RPM Switch is a ground.

Does this car have a transbrake in it?

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Re: msd 7531 with nitrous

#3 Post by raffaplymouth » Tue Nov 03, 2015 8:27 am

Hi John , i know this is not for street but i have buy the 7 AL for cheap price !! car is footbrake , Therefore , if i have understand ....if i select last gear 2 on software to MSD with correct plot ( no connection on gear select wires )

i will connect from nitrous solenoid +12v to step retard and will retard what i set ???

i have used this solution but i dont know if is correct , i have put the total timing at 38 degree with trigger adjust

selected gear 2 , because gear 1 is not possible select , i have make a curve map plot from 800 rpm to 8000 rpm like my old mechanical distributor :

800 rpm 25 degree

1800 rpm 30 degree

2500 rpm 38 degree until 8000 rpm

the engine runs perfect

therefore you think is not important the gear select ?? if when put the nitrous will retard from step wires ??

[nitrous activation now is with a microswitch on the shifter when engaged 2nd and delayed of .02 with delay box.... I leave that as is, or should I use a function of 7531 ??
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Re: msd 7531 with nitrous

#4 Post by John_Heard » Tue Nov 03, 2015 8:51 am

Yes, if you hook the Nitrous Solenoid power to the Step retard input, ANYTIME you turn the nitrous on the retard will activate - that is what those Step retard inputs were designed for. This is important. If your nitrous activates and for some reason your gear setup like you have it doesn't work as planned, you'll hurt the engine.

In regards to trying to mimic your mechanical advance, I have never attempted to do that on a 7531 box, it wasn't designed for that. You could certainly use the Gear Retard functions for Gear 1 and 2

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Re: msd 7531 with nitrous

#5 Post by raffaplymouth » Tue Nov 03, 2015 9:06 am

John_Heard wrote:Yes, if you hook the Nitrous Solenoid power to the Step retard input, ANYTIME you turn the nitrous on the retard will activate - that is what those Step retard inputs were designed for. This is important. If your nitrous activates and for some reason your gear setup like you have it doesn't work as planned, you'll hurt the engine.

In regards to trying to mimic your mechanical advance, I have never attempted to do that on a 7531 box, it wasn't designed for that. You could certainly use the Gear Retard functions for Gear 1 and 2

John , yes i have mimic my older distributor curve with gear retard and work good ! is possible make in 1-2-3-4-5-6 gear but the first gear is not possible select on software , i dont understand why not .. but this is not a problem

therefore the gear retard shift is not important ? will be locked in 2nd the shift selected ?

another thing that i have not understanded is the rpm drop , what is this ?
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Re: msd 7531 with nitrous

#6 Post by John_Heard » Tue Nov 03, 2015 9:32 am

RPM Drop is how the 7531 knows you've shifted into the next gear. Gotta realized that box is designed to use the launch input wire to start a sequence of events it's designed for, which isn't driving around town.

When the launch wire goes off, the unit knows it's in 1st gear, then when it sees the RPM Drop as programmed, it knows it's in 2nd, 3rd, etc.

From the 7531 instructions -

"The Three Step Retard wires, Pink (1), Violet (2) and Tan (3) can also be wired to indicate the first three gear changes to the ignition control. When selected from the Step Wire menu, the ignition will know that the car is in second gear when 12 volts are applied to the Pink wire, third for the Violet and fourth when the Tan wire is applied to 12 volts. By using this feature, if you lift off the throttle and get back on it, the ignition will not count it as a gear change. Note: When selected, this feature overrides the RPM Drop Gear Select values."

You could use step retards to do this, but the unit has no idea when you shift back into 1st when you stop unless you reset the box using your brake as a launch input I suppose.

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Re: msd 7531 with nitrous

#7 Post by raffaplymouth » Tue Nov 03, 2015 9:38 am

1970 Super Cuda 496 Indyheads
ET 9.32@148 1.42 60ft (250 shot ) :shock:

raffaplymouth
Posts: 162
Joined: Tue Jul 24, 2012 2:07 pm

Re: msd 7531 with nitrous

#8 Post by raffaplymouth » Tue Nov 03, 2015 9:47 am

this is my engine compartment now with new Dominator intake and carb and new double cross plate .... this year i had big problem horror stories with NX perimeter plate !! , very high misfire over 200 HP jet !! ... i think this plate will be better !! now is setted at 300 HP
1970 Super Cuda 496 Indyheads
ET 9.32@148 1.42 60ft (250 shot ) :shock:

raffaplymouth
Posts: 162
Joined: Tue Jul 24, 2012 2:07 pm

Re: msd 7531 with nitrous

#9 Post by raffaplymouth » Tue Nov 03, 2015 9:54 am

John_Heard wrote:RPM Drop is how the 7531 knows you've shifted into the next gear. Gotta realized that box is designed to use the launch input wire to start a sequence of events it's designed for, which isn't driving around town.

When the launch wire goes off, the unit knows it's in 1st gear, then when it sees the RPM Drop as programmed, it knows it's in 2nd, 3rd, etc.

From the 7531 instructions -

"The Three Step Retard wires, Pink (1), Violet (2) and Tan (3) can also be wired to indicate the first three gear changes to the ignition control. When selected from the Step Wire menu, the ignition will know that the car is in second gear when 12 volts are applied to the Pink wire, third for the Violet and fourth when the Tan wire is applied to 12 volts. By using this feature, if you lift off the throttle and get back on it, the ignition will not count it as a gear change. Note: When selected, this feature overrides the RPM Drop Gear Select values."

You could use step retards to do this, but the unit has no idea when you shift back into 1st when you stop unless you reset the box using your brake as a launch input I suppose.
OK John tonight i will connect the PC and i will make some test
, why you think the box will no reset ???
if when i will return in the first gear the positive at step wire will be disconnected ???
1970 Super Cuda 496 Indyheads
ET 9.32@148 1.42 60ft (250 shot ) :shock:

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Re: msd 7531 with nitrous

#10 Post by John_Heard » Tue Nov 03, 2015 11:04 am

Because in order to reset, you have to activate the light blue and dark blue wires as they tell you in the instruction. The Light blue used for burnout rev limit also resets the box's data acquisition record function. The Dark Blue, normally hooked to the transbrake, resets the box and when released it resets the box to 1st gear, and starts all timers and recording functions.

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Re: msd 7531 with nitrous

#11 Post by raffaplymouth » Wed Nov 04, 2015 11:59 am

hello , i have installed the 7 AL yesterday in this way

gear 2 select with plot curve idle 28 degree max rpm 38 degree

15 degree of start retard until 800 RPM

step retard for nitrous at 9 degree on pink wire ( work good )


i can connect the dark blue at line lock ??
1970 Super Cuda 496 Indyheads
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Re: msd 7531 with nitrous

#12 Post by John_Heard » Thu Nov 05, 2015 8:02 am

No, Dark Blue is the main reset, it's typically hooked up to a transbrake which will signal the start of the run. In your case I'd probably rig me up a switch and connect it to your brake light switch since your foot braking it. When you're racing the car, activate the switch that connects it to the brake light, that will signal the box when the brake light goes off, you're starting the run. This will also let you make use of the data acquisition the box has as well.

The light blue wire would hook to the line lock, that activates your burnout rev limiter and resets the acquisition record function.

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Re: msd 7531 with nitrous

#13 Post by raffaplymouth » Sat Nov 07, 2015 1:58 am

ok let me know if i have understood ....

DARK BLUE at stop switch , when release the pedal at the starting line ( green light on three ) the box will start in gear 1 and remove the launch control RPM that i will be set at 2000 rpm ( i like also with 5000 converter stall )

which cable will active the launch RPM at starting line when i wait the green light ??

LIGHT BLUE at line lock for burnout RPM.

Thanks John !
1970 Super Cuda 496 Indyheads
ET 9.32@148 1.42 60ft (250 shot ) :shock:

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Re: msd 7531 with nitrous

#14 Post by John_Heard » Sat Nov 07, 2015 7:58 am

The Dark Blue wire when active will activate the Launch Rev Limit. yes, I think you have it all correct now. Again, you might want to put a switch in line with that Dark Blue wire going to the brake light, activate the switch when you finish the burnout and get ready to pull up to the line.

IF you can remember to flip the switch AFTER you launch like right before you hit the brakes, it will avoid resetting the box again. That way your data will stay intact in the data acquisition. If not, when you hit the brake to stop, it will reset the box again (if RPM is high enough). Hope that is clear how this works.

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Re: msd 7531 with nitrous

#15 Post by raffaplymouth » Tue Nov 10, 2015 9:53 am

hi ..I have no make other modify at the wires ... I have drived the car all day with no issues. .. this morning the car won't start !! no spark ! and the led flash two times! !tried at disconnected and connect all wires is OK positive and ground is OK. .. Help @!
1970 Super Cuda 496 Indyheads
ET 9.32@148 1.42 60ft (250 shot ) :shock:

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