308 dual dizzy options.

Wow, I am new here and am trying to learn what is going on with this particular topic. I have been asked to develop a clean solution to replace the dual diatributor points ignition in a friend's 308gt4 with better reliability and configurability. His dersire is to retain the OE look with 2 coils and 2 distributors. It appears that there is an ongoing quest for solutions here as the installed base of this system system is getting older and more maintenance intensive.

He has asked that I have a single discreet control unit (hidden) and retain both coils/caps/rotors for the stock look. He does not want to go to crank triggering as I do not want to get that deep into the car, but have collected the parts to do a conversion on one distributor to get a rev signal. We will use a crane optical pickup and a custom wheel. We will disable both mechanical advance mechanisms as advance is controlled in the electronics. There is as option to connect a vacuum spource from the intake to get a bit better economy in cruise. The ignition curve will be adjustable via a laptop computer. Connections required would be 12V, gnd, a wire to each coil and a cable to one distributor. You should be able to retain the existing tach with no modifications. as it is triggered off one of the coils.

Is anyone else here interested in such a setup? At what cost? It could be duplicated after we get it running. If there is no further interest, that is just fine and I'll convert over this gt4 and call it done.

Now, the accuracy could be improved with the purchase of a crank trigger and sensor pickup bracket from: http://www.durable1.com/trigger_wheel.htm. This option would 4 coils. 2 coils is probably decent to 6k rpm. After that, you will drop off in spark energy. 4 coils would give you enough spark energy to rev past redline with no drop off in spark.

The drive electronics we are using is Megasquirt. The firmware is MSnS-E. There are some hardware modifications to drive the coils and I would configure the software basics. The coils can be 'any available' (MSD, Ford, Dodge, GM, basically any distributorless coilpack), so the cost for aquisition and replacement of those should be cheap. I have been running this on my 4cyl turbo for ~year now with no issues. The electronics can also run the complete EFI if you intend to go that way, but my initial thought is to get a reliable spark for this dusl dizzy configuration. This is similar to Electromiotive's XDI system, but at lower cost. Interest?

If you have read this far... We also looked at a 8 cyl conversion. The rover 3.5L v8 OPUS cap ('80 and '81? maybe more years) is the right diameter and height. Slight modifications may make this an attractive choice as well to convert from the marelli 4 pot cap to an 8 pot one with appropriate internals. Thought I'd mention this as well.

Feel free to PM me or drop me an email.

Regards,

Keith

 

Thanks for the response. The need to calibrate a mechanical distributor is what I want to go away from. We will make a special disc that has 32 slots in it, read out these slots with a crane optical pickup, feed this signal to the control unit. The control unit will be programmed with the specifics of when the triggers happen and what to do about them (dwell then fire the coils). The control unit will control dwell and timing much more precisely than the mechanical distributor could ever AND I do not need to precisely align 2 crane or pertronics units in a single distributor. The electronics has enough smarts to do all that for us, basically use 1 pickup with enough triggers to fire both coils.

KeithG

 

Do you already have the MOTEC unit? That appears to be a very capable system. What pushed you to COP? If I do my math right, wasted spark is more than adequate for streetable engines that don't run too many revs. 10k rpm gives you 6us per rev and coil dwell should be about 4us, so that should be 2us to spare. What am I missing? I am looking at a COP on another install, and am going to go trounce through a junkyard to see if I can adapt a cam sensor from a ford or something.

KeithG

 

Well, I have been moving forward on this. The board is complete and checks out on the bench. We have decided to get one of those durable-1 wheels and sensor mount. This makes life much easier for us as long as we can get the trigger on the lower pulley.

We need to generate an ignition map, so I was poring over the 308gt4 manual and a writeup on the distributors to get a map...

This look right:
6 6 6 18 20 25 29 34 36 38 41 43
500 800 1000 1500 2000 3000 4000 5000 5500 6000 6500 7000

top row advance, bottom row rpm.

Oh yeah, can these motors take decent vacuum advance? Anyone try it or know? This controller has a 2d map (rpm and manifold pressure) and I can map some more advance for cruise conditions. If not, we will see. Just thought I'd ask. Right now I am pushing it to 47 or so. We will see how she takes it.


KeithG

 

oh yeah, can these motors take more advance at low load? I thought that since it was an 8V low compression engine that a bit more advance at low load (high vacuum) would be helpful for drivability and mileage. Anyone tried it? Anyone willing to share an ignition map?

KeithG

 

What if there were a less expensive solution than this, would it be interesting? What if the solution could drive either both coils with the existing caps and rotors or 4 coils for wasted spark and was user configurable to do either? We are waiting for the durable-1 ring and will be ready to try it out as soon as we get it. We will post here with results. Is there interest in a conversion kit to convert from the marelli distributor caps and rotors to ones which are more available?

KeithG