Crank Trigger & Mag Timming?

A mag cap has 8 plug terminals which mean that there are around 45 degrees between each adjacent plug wire terminal. So if you divide the 45 degree evenly you have 22.5* so that is the max theoretical timing change you can have from the phased position of the rotor being exactly across from the plug wire before the spark will go either way. That is theoretical and if the plug that is meant to be fireing is a little fouled or the plug wire has a little more resistance than the wire next to it the high voltage will take the path of least resistance and jump to the other adjacent terminal inside the cap. The larger the diameter of the cap the further apart the terminals so the safer it is and thus the newer super mag cap that MSD makes mainly for TF cars that change the timing 40+ degrees. TF cars will split the difference on rotor phasing because they change timing so much so if they move the timing by 40 degrees during the run they will phase the mag at 20* depending on the point in the run the spark may fire with the rotor 20* before the terminal and then may fire 20* after the terminal.

Realistically you can probably safely go 12-15 off from were the rotor is phased without a problem. For alcohol cars that are only moving the timing small amounts the spark jumping to the adjacent terminal is not such a big problem so if only changing 12* or less they can both be run on the same degree with no problems. If you start changing the timing through the run more than 15* then you might want to consider splitting it some just for safety margin.

 

Yes, I guess I misseed that one, you are correct on the degrees.

According to MSD the big caps are to stop the cross fire on adjacent terminal with big timing changes such as with TFs. With a crank trigger you can phase a mag with any size cap but without a crank trigger you need the adjustable or moving cap.

 

To put it a little simpler in a perfect world you want the crank trigger to fire the mag gewnerator when the rotor is exactly opposite the spark plug terminal in the cap.

If you don't use a crank trigger you set the timing by turning the mag just like on a regular car and it is always in phase or pointed exactly the right po9sition.

If you have a crank trigger you adjust the timing by moving the crank trigger pickup sensor. This means with a crank trigger it is possible to have the crank trigger fire the mag with the rotor pointed in some position between two spark plug wire terminals in the cap. If the rotor is not pointed within so many degrees of a terminal in the cap when the crank trigger fires the mag means that it is out of phase. To bring it back in phase you need to twist the mag so the rotor fires within so many degrees of the cap terminal. Some times you can be so far out that the motor will not start or the spark will jump across inside the cap to the wrong terminal.

If you do not run a crank trigger and do not change your timing more than around 8-9* going down the track then it is not a big deal and will not make any diference. If you have a crank trigger and do not change the timing more than a few degrees then you can put the timing pointer on 27* drop in the mag and adjust the crank trigger pickup so it is directly across from a magnet in the crank trigger wheel. When you start the car and fine adjust the timing the mag rotor phasing will be real close that it is close enough. You can also take an old mag cap and drill a hole just inside of number one plug wire terminal and shine a timing light through the hole with the motor running and actually see the rotor to cap relationship. I usually put a dab of white paint on the middle of the top of the rotor tip so it is easier to see with he timing light. You can carefully turn the mag base until the rotor is pointed to where you want it. You can energize any timing circuit at idle and set it where you want it at what degree you want.

 

I have never pushed the limit with a ProMag 44 but in heavy nitrous use when we were retarding 22* during the run we always phased the rotor with the 22* retard in because 99% of the run was like that and we never changed it more than a couple of degrees during the run. That meant that during the burnout the rotor was at least 11* out of phase and we never had problems. I myself have never seen a blown alcohol motor ever change the timing that much. I would say that with a blown alcohol motor with the standard ProMag cap that you would run them the same and not split them.

 

blown alky

we've retarded as much as 14 degrees with our car...with lencodrive. we run the big cap. the one lap we had the trigger on it, i think the most we pulled out was 12, and had the mag phased in on the same setting as the trigger.

we just switched to crank trigger. when we got the new racepak and monitored timing with just mag trigger, it really got our attention. we got the top of the line mag drive, big shaft and all that, and i have almost no end play on the cam, and it still jumped around. i was always scared to have something else go bad, but i was unaware how bad the timing jumps around.

you can get the whole set up to switch to crank trigger pretty reasonable from JR at RBS!

 

mag trigger

no, we started monitoring timing when we were triggering the mag off the drive rather than crank trigger. that was atlanta, we switched to the crank trigger in shreveport. timing is dead on with the crank trigger. hope that helps clarify...