CDI and twin spark

[Peter M]

Originally Posted by MZ3 SBC

thanks for that explanation. I absolutely follow you. I missed that important detail in the Ignition Timing Sticky Thread- that twin plug dizzys dont have vacuum advance. Whether that be all or some, I can say definitively that I have a single pot dizzy. I like the idea of locking out the dizzy and using the programming of the CDI+ ..the J&S is not laptop programmable so I wonder if it is contolling the advance curve or if the dizzy is...I have a good feeling it is not since the distributor is not locked down.

Erik,
I think your next stop would be a programable ignition only ECU like the Haltech VMS that would allow you to map ignition timing against engine load and then use this ECU to trigger the CDI unit.

More on the Haltech VMS here: https://www.haltech.com/product/ht-157000-elite-vms-ecu/

However given the cost on such a unit, you would be tempted to bin your old K Jetronic fuel system as well and go to a full EFI ECU that controls everything easily and seamlessly like a modern car.

[MZ3 SBC]

Originally Posted by Peter M

Erik,
I think your next stop would be a programable ignition only ECU.....
However given the cost on such a unit, you would be tempted to bin your old K Jetronic fuel system as well and go to a full EFI ECU that controls everything easily and seamlessly like a modern car.

Thanks for the suggestion. And there lies the rub!! Quite a slippery slope. I am enjoying the process of seeing what options are out there. This is too big a decision to just jump. My next step will be to consult with my engine builder and revisit my goals.

For Igniton I have 2 Bosch CDI boxes, 2 black coils, recurved Bosch twinplug dizzy ( not sure if it is modifeid or original) and have the Safeguard unit to pull timing under boost. I am told its all I need....but can it be improved on with either upgraded CDI+ boxes or going smart coil and ditching the distributor. It would be nice to know that any changes are improvements and can be paired to a full EFI conversion in future.

Maybe for me there is little need to make any changes....when do needs and wants and a 930 go hand and hand!! I really dont need more horse power but a llitte more would not upset me. I would like a litte more low end torgue below where the 7006 hits....and I think that could potentially be met with a 7200 Raptor of GT25r ball bearing turbo.....the latter being preferred BUT.....

The Safeguard pulls timing to a max of 16 degrees when it gets a boost signal ( not sure how but I do know that it is prgressive and can adjusted in up to 2 degree increments) and the recurved distributor may already be giving me all the vacuum advance I need off boost.

To your point if I get an EMS sytem to control ignition then I am onestep closer to EFI...


I read an old post today that a properly running and improved CIS system can handle 400-450 whp... WOW ....seems more than I thought was possible.
Now is that 450 on a dynojet or on a mustang dyno?.....all dyno hp is not created equal. What I do know is I have approx 350 mustang dyno hp at .9 bar on a fully built 3.4 and with an 8.41 ratio its more than enough and often too much to use it all before running out road.


If I have the fuel to safely run 1 bar at get a safe 375-400 ponies....and good crisp off boost low rpm respomse I would be happy....

heck....I am already HAPPY.....

[Peter M]

Originally Posted by MZ3 SBC

To your point if I get a full ignition EMS sytem ( which I dont see why thats better than programmable CDI+) and get the timing set ...I spending a good amount of money...why not go EFI.

Erik,
Sorry I wasn't more explicit, the Haltech VMS has a built in manifold pressure sensor so it gives you the ability to map your ignition timing against engine load as per your original enquiry.

As a happy Motec M130 owner, I wouldn't entertain separate systems when it can all be done easily in one black box. Admittedly not cheap but very good.

[MZ3 SBC]

Originally Posted by Peter M

Erik,
Sorry I wasn't more explicit.....
Admittedly not cheap but very good.

Thanks Peter. I appreciate the suggestion...and certainy am not scoffing at it. SO many choices and options. I am open and will make an informed decision. My last diatribe was ceertainly not aimed at anyone partucular suggestion in a negative way... I have been to the rodeo more than once and rode the clown pony ...so when it comes to a big decision I like to review the options.


Few have said it hear and it resonates.....chose a program that the tuner is familiar and comfortable with. I am not familiar with Haltech as of yet and went straigh to the website.

Some love AIM some love Motec....they probably all work great provided they are set up to meet the drives goals.....Is $$$$ always betternthan $$?

Nothing is cheap with these cars....so I want to do it rightthe first time..... if I am going to spend the money...I would prefer to upgrade the cars reliability and performance rather than repair / rebuild becauseof a failed part thats 42 yrs old. My WUR ruptured the other day and I could burned the car to the ground.. had no idea the old diaphragm cant handle .95 bar boost..I sent out for rebuild only to read later same day about a digital WUR!!! I would have like to consider that option...

Driving season is short in North East

[LM3929]

Is there any consensus on whether or not a CDI or CDI+ box will trigger two coils?

Lorne M.

[troth]

Originally Posted by LM3929

Is there any consensus on whether or not a CDI or CDI+ box will trigger two coils?

Lorne M.

Lorne,
I recently inquired at classic retrofit about this and this is the reply I got:

Hi Tom,

You need two boxes. At the end of the day, this is electronics and physics. If you put 2 coils in series or parallel with a single box, you change the characteristics of the circuit. Both configurations result in only half the spark energy being presented to the flame front. This is counterproductive if the reason for going with twin plug is to gain power.

Regarding the failure of one box in a twin plug system, I don't agree with the 'severe detonation' comment. In a twin plug engine, because there are two flame fronts, the fuel 'burns' faster so there is less need for timing advance. Indeed, if you check the specification of timing for a twin plug engine it is typically 5 degrees less at full advance than a single plug engine. So, if one box or coil was to fail, the net result is that the ignition would in effect be further retarded, not advanced. Retardation of the ignition typically does not cause detonation - in fact it is used to prevent detonation in many engines. You would also notice a significant drop in power from the driver's seat so it would be immediately apparent. The only negative affect of prolonged use of an engine with retarded igntion would be an increase in cyclinder temperature, however this would take a little while and you'd have noticed the drop in power long before that.

Food for thought: Consider the latest trend for COP in a twin plug application. There is typically no warning mechanism for a coil failure in those systems and modern coil pack failure is a fairly common event if my modern car is anything to go by. Now, if one of those COP were to fail (eg. one plug in one cylinder), I very much doubt that the driver would notice. They would continue to use the car and that cylinder would heat but it probably would not be detectable in engine temperature or significant power loss. I would regarding this as a far more 'dangerous' situation for the engine compared to the traditional arrangement of two coils and two CDI units.

Best Regards,

Jonny

So it seems, no, the CDI+ cannot be programmed to output twice the energy and split to two separate coils in parallel. This was surprising to me. I know other vendors like ashlock can modify stock cdi boxes for twin plug by installing two sets of solid state electronics in a single box. I would think classic retrofit could do something similar. I’m sure their circuitry takes up more physical space, but it seems there would be a market for this. A programmable curve in a stock looking box to plug into a locked dizzy by JB racing or similar. They recommend using MSD, but I prefer the stock look of the Bosch cdi boxes.

[Neil Harvey]

For those that may be interested, I have dual channel CDI unit that can drive 2 coils without halving the energy output. Unfortunately it can only be triggered with hall sensors. If there is interest in just the CDI I could come up with a replacement sensor for those distributors with reluctors.

[blucille]

I had Bob ashlock build me a "custom" twin CDI box inside one enclosure....it's neat and tidy. Cool features everywhere, it lets me put it in points/3-pin mode or 6 pin mode, so its a great universal spare, too.

https://ashlocktech.com

[Jonny H]

Originally Posted by troth

Lorne,
I recently inquired at classic retrofit about this and this is the reply I got:



So it seems, no, the CDI+ cannot be programmed to output twice the energy and split to two separate coils in parallel. This was surprising to me. I know other vendors like ashlock can modify stock cdi boxes for twin plug by installing two sets of solid state electronics in a single box. I would think classic retrofit could do something similar. I’m sure their circuitry takes up more physical space, but it seems there would be a market for this. A programmable curve in a stock looking box to plug into a locked dizzy by JB racing or similar. They recommend using MSD, but I prefer the stock look of the Bosch cdi boxes.

The issue is heat dissipation, for high RPM in a high ambient conditions, a stock Bosch CDI will see a case temperature of over 80 deg C. You put twice the energy in that little box and I think you'd be into forced internal cooling with a fan.

Bob has clearly been playing with this. How are you managing the heat Bob?

[Rosco_NZ]

I think the consensus is, it will work but it may not work forever .. it becomes a reliability thing as the output stage of the CDI box sees either half or double the impedance, depending on whether the coils are in series or parallel. Both have drawbacks. Installing 2x programme-able boxes seems to be the best option for our 911’s …

[rory gallagher]

Originally Posted by chris_seven

I am sure you need two boxes.

I believe that the RSR used an 8 Pin Box but if you have an SC dizzy with a mag pick up you can use 2 x 6 Pin Units.

To run two 6 pin CD units (for twin plug) I can piggyback a second green wire onto the single plug into the dizzy ?
If so, I can then adapt a 12 plug cap and rotor onto my (recurved) SC dizzy and have
a working system ?
Any insights are appreciated.
TIA
Rory

[Fred Winterburn]

I don't have the particulars or Bob's design, but he is not using the Bosch design for his dual output CDIs. All I know(or think I know from some correspondence) is that he uses power supplies with a few hundred kHz to keep the size and heat dissipation low while maintaining high rpm capability and power. His CDI designs are nothing like the Bosch CDIs that he rebuilds. Fred

Originally Posted by Jonny H

The issue is heat dissipation, for high RPM in a high ambient conditions, a stock Bosch CDI will see a case temperature of over 80 deg C. You put twice the energy in that little box and I think you'd be into forced internal cooling with a fan.

Bob has clearly been playing with this. How are you managing the heat Bob?

[Speedy Squirrel]

Turbo’s have no appreciable piston dome (lower cr), so twin plug is not as effective/required. Twin plug requires/demands less ignition timing. Some people interpret this as less chance for knock. This is not true. Combustion is faster, and produces higher cylinder pressure. It makes slightly more power (around 5%) for this very reason. Faster combustion has less time for heat transfer (loss) to combustion chamber. Big dome pistons benefit considerably more, 10% or more, because of the flame propagation issue being lessened.

CDI multi spark is kind of like mopping up. CDI spark duration is notoriously short. More sparks give CDI more chances to ignite the mixture, in case it missed it the first time. Once the O2 near the plug is consumed though, that’s all she wrote.