NHRA Legal MSD Timing Control

I agree that the rule change was not really thought out or NHRA has some other agenda that I couldn't figure out. On our ProMod we use the MSD 8973 Pro Mag Digital Controller that has one time or RPM switch (only one) that controls a electrical solenoid for the high speed lean out. It is direct with no other air interface and makes it real easy. Changng the main jet does not change the pressure at the high speed lean out poppet. I use use Digi-sets to electrically control other solenoids for fuel control. Why NHRA still wants to complicate things with electric over air has me totally confused.

 

We use a clutch switch and a WOT in series to start our secondary Digi-Sets. The primary RPM switch/time switch in the 8973 is initiated by the clutch switch. The 8973 has to have a 12 volt reset wire (medium blue wire) that both resets and initiates the box. The 12 volt signal is applied to the box when the clutch is in and this resets the box into a "get ready to go mode". The reason this is required is it has to know that you are starting in first gear so it can reset all the retards, the timer, and the adjustable shift lights for each gear. Without that reset wire the box is lost in the ether. So take this as a warning. The same reset function is used on the Digital 7. I have had guys call me up and ready to pull there hair out because they didn't read instructions.

Here also is some good data that took me a while to learn. If you have looked at the MSD software for a 8973 or a 7531 on your comuter you will see several timing curve graphs on the right side of the screen. The one at the top is called the "Launch Retard Curve" but that is really the 1st gear curve and is only used when you are in first gear. Once you shift it changes to the "Run Retard Curve" for 2nd and 3rd gear. (If you haen't looked at the software this is going to be confusing). If you fired up the motor without the clutch in (which you never do) both the 8973 and the 7531 start in the "Run Retard Curve" and stays there until you push the clutch in and give the MSD a 12 volt signal then it switches to the "Launch Retard Curve". So as long as you have he MSD wired correctly this is transparent to you but you can see what happens if you don't hook it up right.

Now you totally understand that then let me continue to scramble your brains. The way I set the timing is at 30* at idle and then I have the MSD box pull out 4* so I am at 26* actually. I put 4* retard into both my Launch Retard Curve and my Run Retard Curve and in my brain I let that be 26*. The first time I start it I use the timing light and adjust it so it is right at 26* with the 4* in the MSD box. So from then on if I check the timing with a light and it reads 27* then change my Curve by another degree to correct it to 26*. I never have to move the mag with the motor running and get zapped and let it go again. Now using my baseline that got me to 26* I, ontop of that, advance and retard the ignition based on RPM. Where it gets complicated is if you launch at 29* and want to pull out 3* at 7500 RPM and then stay at 26* (all made up figures) for the rest of the run then you have to start the Launch Retard Curve at 1000 RPM at -1* retard on the graph (really 29*) and then at 7500 go to -4* on the graph(really 26*) in the rest of the Launch Retard Curve and all of the Run Retard Curve.

If you never want to change your timing through the entire run then you can have zero degrees in the Launch Retard Curve and the Run Retard Curve and set the timing exactly where you want it at 26* and adjust the mag just like you have been doing it.

Also remember that all the retard functions add together when each one is activated.

 

And no you do not need the retard box or a six shooter anymore. Sorry forgot.

 

Yes you can use one of the three switched auxiliary retards. You can wire in a switch to either of them to be turned on just during burnout. You also have a burnout RPM limiter than can be used in conjunction with it. That leaves you two auxiliary retards that can be activated via a 12 volt switched source such as air/electric switches or timers. I think you are going to have to switch to a timing curve to try and get the same thing as you are doing now.

 

Since we have yet to have a failure that has resulted in an overboost I was wondering how much the boost will go up with one cylinder out. 2 lbs, 4 lbs or what? You need the Racepac boost sensor to make that function work.

 

As far as I know the 7530 does not have a time retard function such as what we are talking about in the 7531 or the 8973 so I don't know what default time for retarding timing you are talking about is. Explain it more to me.

Since a 7530 does not have built in selectable firing orders like the newer boxes it doesn't make any difference which you designate the first cylinder to fire in a sequence. What you have to make is a cheat sheet to carry with you that will tell you what the order is if you start at #6 being #1 and continuing on. The only time the Digital 7 uses that sync fiber optic line is right at start up for a few revolutions then it doesn't use it anymore until you shut the box off.

 

Just so we are talking the same. i believe that function is called the Launch Retard that can be set from 0.0 time to a max 2.5 seconds in .01 second intervals. Is that correct. I know of no other timed retard.

 

The individual cylinder timing option is used to make up for crankshaft twist or other problems in uneven timing. On a nitrous motor and a blown alcohol motor I read the position of the "Blue Line" on the spark plug ground electrode to show me where the timing is in each cylinder. If 5 or more read in the same position I will adjust the other 3 individually to make them all agree. I do not know if a nitro motor makes a "Blue Line" on a ground strap.

Try this link for the software download
http://www.msdignition.com/1softdownload.htm