Compu fire DIS ignition ?

[CAVEHEAD]

Has anyone tried this new ignition system for type-4 (411,412 or 914) ? I've used PerTronix on multiple Type-1 1600 beetle engines and have enjoyed the contactless system

[Jeremiah Berger]

Mine has an older setup that is called a fireballxc700. It is basically the same thing. It has never had a problem. Was in it when I got it. I also have the flamethrower in my beetle and am pleased.

Jeremiah

[raygreenwood]

So the compufire DIS....is the "distributor-less" model right?

Its not REALLY distributor-less as so many threads over the years have ranted about (which is fine)....all it gets rid of is the points (with a module) and the rotor and distributor cap. You still have wires from a four pin coil pack/tower.

I have never used a DIS. But I do not really have a problem with it because as nicely built as the GOOD Bosch parts like the distributor cap and rotor are.....they have some variation. They used to have less. They have more now.

What I will say now is a bit of a tangent and I do have data to back it up but I will not be doing a full expose/layout until my car is back on the road.

But for the moment I will direct your attention to a couple of items.

1. If you ever have your engine idling and with gloves on...shift the cap around a little from side to side....you will notice a rough change in idle. I did not say rotate the cap or twist it against the spring force of the clips....that would change timing. I mean slip or slide the cap in a straight axis.

What I have found is that most type 3/4 distributor bodies are right at 2.50" to 2.55" and the caps are right at 2.59" to 2.62". What this means is that there is anywhere from 0.040" or larger for slip and slide room for the cap.....so 0.020" or larger of movement.

This means that depending in which way it's pushed, the gap between the rotor and and given output pin for a cylinder/wire can be a good bit off.

Depending on how good your bearings are and your points cam....You have some variation from the rotor position too.

2.all of the above and issues with points as they carbonized from the arc....and this is the vast majority of where timing variation or spark scatter comes from that far too many complain about.
There is a lot of that in the points mounting and advance plates too....so see my points plate how to to get rid of a lot of that.

So bluntly put in my opinion....a lot of the yakking about "spark scatter" is unfounded......or exaggerated.
Many say it comes from the distributor drive gear....and therefore one must go to direct fire....but unless your crank timing gear is just screwed up....that's a constant load joint. Very little variation.
I have found that as long as your distributor bearings are tight, you take the slop out of the points plates, your points cams are within a couple thousandths of esch other (not worn out) and you have taken the common excess axial slop out between distributor drive dog and distributor body (it only needs about 0.010" max)......my distributors typically hold with +/- 0.5 to 1.0 degrees. Rock solid.

But back to the subject.

The DIS replaces the points with a module. That's a good thing. I have found that alone creates a steadier, more uniform spark timing signal....if your points cams were slightly worn or rough. The magnetic module is less sensitive to that......but you cannot be grossly off....because there is SOME sensitivity to gap.

And the magnetic switch versus points...is closer to a real "square wave" on off signal instead of a variable ramp. Does this make a difference?
Yes....with D-jet especially...and especially with a better coil like the Flamethrower which I highly recommend.
The higher compression D-jet type 4....is barely ignited by the stock coil at higher rpm.

With that coil.....the module makes a noticeable enough difference in running....because of how sensitive our system is to any input change....which changes fuel...which changes running which changes fuel etc. etc......a cascade......that just going to a compufire or pertronix basic module....cleans up idle...and in most cases allows/requires a slight tweak to fuel mixture on the MPS.

The rest of the DIS package....no cap or rotor....I think could clean it up a little further.

Ray