NZ951

As topic...

turbite

You going dual coil wasted spark?

Ben Z.

How hard would it be to just make one?

NZ951

Prety easy Ben, but I am too busy making something else at the moment I think Danno or Chris have one lying around from memory.

Chris White

with or with out cam sensor mounting?

Chris White

TurboCab

I have this for sale at Ebay:
Crank trigger kit

NZ951

Chris, could you please explain the differences? I am doing this as I will be running sequential injection off the Link...

Chris White

If you want to go full sequential you need to know the cam position. In theory you can go with out a cam sensor but then you run a 50/50 chance of opening the injectors during the exhaust cycle instead of the intake cycle – makes for a lousy idle.
The block off plate I make is either ‘blank’ for non sequential or it has a hole and additional support for a threaded hall effect sensor along with a small trigger wheel. This works well with the Tec3 - system. – other systems may prefer magnetic sensors.

This is one of those ‘fun’ things that you need to figure out when setting up a different system – if you like experimenting and trying to solve puzzles it is a fun challenge, if you just want the added performance the look for a system that is set up for the 944…..

Chris White

Porsche-O-Phile

Forgive my ignorance on this, but my knowledge of the variable ignition timing system is somewhat limited. On the stock 944s, there is the distributor on the front of the engine that completes a circuit to the appropriate plug wire from the coil based on rotor position. This makes sense. How then does the computer control the spark timing - it can't "move" the rotor - either the circuit is open or closed. I'm wondering this for a couple of reasons - (1) I'm trying to understand what you're doing and how you'd control it and retain variable ignition timing by the DME and (2) trying to understand exactly how my MSD 6A box works for the Callaway car. I have it and I'm sure I can hook it up, but I'd feel better knowing exactly what the heck it's doing. Thanks all.

Chris White

That’s OK Jeff – it just shows me that you are at least over 30….

In the good old days of distributor based ignition systems the timing was set by the ‘points’ in the distributor body opening and closing – this sent the trigger voltage to the coil so it could fire. Rotating the distributor changed the point at which the ‘points’ would open and close – that was how you adjusted the timing (its not the relation ship of the rotor to the cap – that does not make a difference – sparks will jump quite a distance!)

The spark timing in modern stuff is all computer controlled via the DME and when it fires the coil.. Nothing you can do to the distributor will change that. Its all done with chips.

Chris White

Porsche-O-Phile

Thanks, yea I'm still a bit too old-school in my thinking. I remember having to twist distributors to adjust timing, etc. I just wasn't sure how the computer could control a circuit that ultimately seemed controlled by mechanical means (cap & rotor). I guess as long as the computer tells the coil "now" within the tolerance / limit determined by the spark's ability to jump within the cap from rotor tip to "point" (to corresponding plug wire) it would still work properly.

Someone asked a while back whether the wire position mattered and to my knowledge (some others said this too) it doesn't - as long as you have the sequence of plug wires correct going around the cap correct it should work (right?) This is a bit counter-intuitive since you could have the rotor pointing to the #3 cylinder contact, but the #1 (or whatever, another one) will fire! How the heck does that work, or is the explaination that the wire position doesn't matter incorrect? I've just always done straight R&R - if you remove the #1 wire, you connect the new one up the same exact way as the old one you removed. This isn't really "thinking about it", but I've never had a problem with something not working either!

IIRC the caps on these cars can only go on two ways. I suppose if you got the sequence going around it correct (clockwise) and the engine didn't start you could just rotate it 180 degrees right?

Chris White

Wire position does matter – besides, there isn’t much slack in the wires to get them out of synch!!

You do need to get the proximity between the rotor tip and the cap (wire) contact correct, the spark is going to jump to the closest contact and fire that plug.

The 944’s used to have a little sticker showing the wire placement.

Chris White

tazman

Jeff the wide head on the rotor is what gives the DME the ability to fire the plugs at different times.

NZ951

Chris, I think I will just run wasted spark for now... so a blank plate would be fine. Could you please PM me the price, cheers!