Twin Spark Firing using single CDI Box

[Neil Harvey]

Just to get good info out there for those that are considering inductive ignition.

All the energy dispatch at the spark plug is generated within the windings of whatever coil you are using.

The igniter add nothing. It has to be capable of carrying high electrical loads but nothing that ends up at the plug tip comes from the igniter.

To run two coils from one igniter channel will always overload the internal transistor within the igniter. They run hot even with one which is why often heat sink paste is used to transmit the heat to a larger heat sink.

[winders]

It's not that simple.

Here is an interesting read:

Ignition Systems - Basics to High Performance

Inductive Discharge vs Capacitive Discharge Ignition (CD)

All of the above descriptions are examples of Inductive Discharge type ignition systems. The first high performance ignition system design was the Capacitive Discharge Ignition which uses high voltage stored in a capacitor to induce the few hundred volt pulse into the secondary instead of generating it in the primary as with an inductive system. In a CD system a high voltage oscillator circuit charges a capacitor. When it is time for a spark, another circuit discharges the capacitor into the coil primary. The voltage produced from the secondary is in the same proportion as with an inductive system. For example if the capacitor is charged to 400 volts, a 100:1 coil will produce 40,000 volts (or there abouts). CD ignitions have certain limitations depending on design. As an example if the oscillator is not powerful enough, the capacitor will not recharge quick enough and the ignition will have an RPM limitation. As you engineer more powerful oscillators, power consumption also increases. As the size of the capacitor is increased, the output of the ignition also increases, however the oscillator must be made more powerful. Certain tradeoffs must be made in design for a particular application.

Compared to inductive systems of the day, CD systems were more powerful since higher primary voltages could be discharged into the coils. One inherent limitation to a CD system is that the spark duration is short due to small capacitors used. As mentioned earlier, spark duration does the actual work burning an air fuel mixture, the voltage is used to initialize current flow across a spark plug gap. Due to the high primary currents of an inductive system, spark duration is naturally longer. Some Manufacturers of CD ignition systems provide multiple sparks to increase overall spark duration. Of course, as mentioned before, capacitors take time to charge up so there are limitations as to what RPM levels a CD system can maintain multiple sparks.

Today with improvements in technology, inductive ignition systems can be made more powerful with special transistors (Mosfets) switching the coil. These devices have higher breakdown/clamping voltages which allow the primary voltage to increase ( 550+ volts) resulting in higher secondary voltages. This coupled with the inherent long duration makes for a powerful ignition which has the capability of also going multi spark. Inductive ignition systems are emerging as the new high power ignition systems.

[Fred Winterburn]

If anyone is interested, I ran a test using a single MSD analogue CDI driving two coils. I posted the results here on the pelican forum. MSD 6A firing two coils simultaneously.

[KNIGHTRACE]

Surely actual measured data is not we need on this thread. Let's stick with feelings and opinions. It is alarming how much power there is left on table today. I have been developing some components for a 3.6 liter motor that actually look by the math that I can get 488 Hp. I do not want to tell the client the number because I have learned If I miss by 5 hp I was wrong.. So I am calling it 475HP. I try to over deliver and under promise. This is not always my result but I try. My first two lines are humor, I was not being serious. In the development of these motors I have found we have lost some very large gains by missing some non important small stuff. It is said we do not need such gains from where these motors are presently but my question is why not? William Knight

[LJ851]

Originally Posted by Fred Winterburn

If anyone is interested, I ran a test using a single MSD analogue CDI driving two coils. I posted the results here on the pelican forum. MSD 6A firing two coils simultaneously.

Wow, Great info !! Thanks for posting that.

I’d still like to hear of others experience and recommendation of a superior CDI system.

[KNIGHTRACE]

The power numbers gained would be shocking.. It seems the more current we apply the happier the motor.. MSD's are weak in my opinion but for a $250 box it has proven more powerful in my experience than a stock Bosch. The reason I said use them is I think a New Bosch was like $700 to the best of my memory if even avaliable. Why not go MSD for the price savings, To get to a high level motor everything in it is different and more expensive. That being said I do not want people to think I only sell exotic parts and builds. I more often than not give cost effective and often free solutions. The euro 3.0 CIS motor with my M1 cam and an MSD will make about 240 HP. inexpensive and great results for the money in my opinion. The Muffler I designed to get the best HP and TQ on this forum I do not even sell, I gave the design to everyone. You can purchase the parts from summit for under $250. We do not have to break the bank to have a fun car but I like that we have the option today to have better than vintage RSR race motors at a fraction of what they cost even if there was enough to go around. I have a factory 1993 3.8 RSR motor in my shop and I often look at it and think how far we have come from that. Speaking of advancements, these barrel throttles have consistently shocked me and make me wonder why did we ever stay with butterflies other than cheeper production cost and more probability. I agree before anyone says anything butterflies may work better than slide valve. I hope all of these post from everyone help some people.

[LJ851]

I agree, William , and thanks for the humor.

[Neil Harvey]

Again I find myself sitting in an airport departure gate waiting for my flight to Florida. About the only time I have to read and post now.

As I have said before, not everyone wants to agree with my posts. That’s ok. If we all agreed it would be a boring world.

I have been using ignition on high performance engine since I started in the 70’s. Ignition is so important and one of my main focus in any engine building.

Like most parts supplied to the aftermarket you have to do your own testing and evaluations. There is way too much hype put out about “how good our stuff is”. Back to back testing should be done or inquire with those that have.

Ignition is a simple mathematic equation. There is one for calculating CDI and one for Inductive. You cannot change the results unless you fudge the input numbers.

For these older Porsche 2V engines with large chambers you need lots of temperature in the chamber. Proper understanding of what actually creates this temperature is important.

In a CDI system the coil acts as a transformer only. The energy is created and stored in the CDI unit. In an Inductive system the coil generates the energy. This is a simplistic explanation but as it works.

There are many COP on the market but none can created the energy a good CDI can. An Igniter is just a simple switch. A little more, but for most it’s just a switch.

If anyone is selling igniters that do more, I would be wary of the hype.

G Gt or those that may be looking for another CDI option, we have been selling one so or over 20+ years with zero failures. You can contact through our PD website.

Like I said before, not everyone wants to agree and there is always someone who will disagree. That’s ok. I base my opinions on what we have tested and proved.

Here’s a simple test anyone can do to prove my opinion. Try starting you engine with fouled plugs with an inductive system. Just make sure you have a spare battery. Now do it with a CDI. It’s the energy released that makes the difference.

[Henry Schmidt]

Originally Posted by KNIGHTRACE

The power numbers gained would be shocking.. It seems the more current we apply the happier the motor.. MSD's are weak in my opinion but for a $250 box it has proven more powerful in my experience than a stock Bosch. The reason I said use them is I think a New Bosch was like $700 to the best of my memory if even avaliable. Why not go MSD for the price savings, To get to a high level motor everything in it is different and more expensive. That being said I do not want people to think I only sell exotic parts and builds. I more often than not give cost effective and often free solutions. The euro 3.0 CIS motor with my M1 cam and an MSD will make about 240 HP. inexpensive and great results for the money in my opinion. The Muffler I designed to get the best HP and TQ on this forum I do not even sell, I gave the design to everyone. You can purchase the parts from summit for under $250. We do not have to break the bank to have a fun car but I like that we have the option today to have better than vintage RSR race motors at a fraction of what they cost even if there was enough to go around. I have a factory 1993 3.8 RSR motor in my shop and I often look at it and think how far we have come from that. Speaking of advancements, these barrel throttles have consistently shocked me and make me wonder why did we ever stay with butterflies other than cheeper production cost and more probability. I agree before anyone says anything butterflies may work better than slide valve. I hope all of these post from everyone help some people.

William, how are you keeping the rotor in a stock Bosch distributor alive using the MSD CD ? Our experience with the multi spark feature in the MSD, you end up melting the resister in the rotor.
The engineers at MSD offer a solution but I'd like to hear what you did/do.

[KNIGHTRACE]

Great question, I have had that problem before, The problem was actually in the star wheel alignment. Sometimes on rebuilt distributers or ones like I made using the magnetic internals into a 964 distributer the magnetic poles are slightly out of phase or alignment. The thing to look for on a burned up rotor like described is if it is burning up the trailing edge or leading edge but most likely the trailing edge. What happens if the magnetic poles are not aligned correctly is it delivers the energy to a small portion of the rotor and with the greatly reduced surface area over the required and applied energy it will burn them up prematurely. The home made twin plug distributer was made by myself. But I usually can get am minimum of 25,000 miles on an MSD unit with Bosch cap and rotor. On race motors usually can get 100 hours no problem. One other thing with MSD and kind of misleading advertisement is the multiple spark discharge. It is only multiple spark for the first 2000 rpm or so.. I call it more of a sales pitch.

[Henry Schmidt]

Originally Posted by KNIGHTRACE

Great question, I have had that problem before, The problem was actually in the star wheel alignment. Sometimes on rebuilt distributers or ones like I made using the magnetic internals into a 964 distributer the magnetic poles are slightly out of phase or alignment. The thing to look for on a burned up rotor like described is if it is burning up the trailing edge or leading edge but most likely the trailing edge. What happens if the magnetic poles are not aligned correctly is it delivers the energy to a small portion of the rotor and with the greatly reduced surface area over the required and applied energy it will burn them up prematurely. The home made twin plug distributer was made by myself. But I usually can get am minimum of 25,000 miles on an MSD unit with Bosch cap and rotor. On race motors usually can get 100 hours no problem. One other thing with MSD and kind of misleading advertisement is the multiple spark discharge. It is only multiple spark for the first 2000 rpm or so.. I call it more of a sales pitch.

Interesting but how do you explain rotor resister burn out in a stock distributor with proper alignment? Even points distributors experience the resistor burn-out.

[KNIGHTRACE]

I typically do not use rotors with a resister in them therefore I may not have an answer for that. I think the primary purpose of that is reducing radio interference. I also do not use the rotors that act like a rev limiter. I am not worried about how clear my radio reception is in my car. I do use the rotor with a rev limiter in it on E stock race cars as it is required.

[Henry Schmidt]

Originally Posted by KNIGHTRACE

I typically do not use rotors with a resister in them therefore I may not have an answer for that. I think the primary purpose of that is reducing radio interference. I also do not use the rotors that act like a rev limiter. I am not worried about how clear my radio reception is in my car. I do use the rotor with a rev limiter in it on E stock race cars as it is required.

I appreciate that answer but in the 35+ years I've been working on Porsches, I have never seen a quality non-resister Bosch style rotor for 911s.
We remove the resister replace with a brass rod and refill the groove with a non-metallic epoxy.
I have seen some pretty cheap/low quality rotors from after market sources but even they are getting harder to find.
Speaking of radio static (I assume you mean RF interference). I have another question about the MSD units you use. They recommend resister wire. All early air-cooled 911s came with solid core wire with resister ends. What do you use and why does MSD require resister core wire? Can you use solid core despite their recommendation?

[winders]

Originally Posted by Neil Harvey

There are many COP on the market but none can created the energy a good CDI can. An Igniter is just a simple switch. A little more, but for most it’s just a switch.

If anyone is selling igniters that do more, I would be wary of the hype.

G Gt or those that may be looking for another CDI option, we have been selling one so or over 20+ years with zero failures. You can contact through our PD website.

You really do need to catch up on current state of the art in inductive ignition systems. It's not 1999 any more.....

[Neil Harvey]

To all those that are interested in learning I hope some here continue to share their knowledge and experience. I will regardless of cheap shots.

My time on this subject is done, but anyone interested in more, are welcome to email me and I will be happy to give help.

[Henry Schmidt]

Originally Posted by winders

You really do need to catch up on current state of the art in inductive ignition systems. It's not 1999 any more.....

Condensing noise like that is what makes you sound ridiculous.

Let me guess....you're going to claim it was just a joke.....my response is simple ...yes you are.

[KNIGHTRACE]

Today as in past years many innovations from race cars spill over into the street world.
This thread has been nothing short of a "DISASTER" in my opinion. I think the questions in the beginning of the thread have been answered. Fred Winterburn gave some good data from his research if anyone still needs help. We need to be careful not to get too technical to the point we do not help the people looking for help. We should help and support each other on these public forums, at least the good guys in my opinion.
My only GOAL was try and help the community.
About Henry at Supertech I have know Henry for close to 30 years.. Henry and myself do not agree on everything but I know Henry is one of the honest resources in the community. We should support the honest people in this trade as there are not that many from what I can tell. When It comes to Niel Harvey I personally do not know him so I can not say but I hope he is a good guy also. I believe it was not my best moment and I was not proud of what I posted, It will not happen again. Thanks, William Knight

[Glenfield]

So, after all that, who is packing the biggest spark ...?

Sorry, couldn’t resist.

[winders]

Originally Posted by Glenfield

So, after all that, who is packing the biggest spark ...?

Sorry, couldn’t resist.

Certainly not a single MSD 6AL controlling 2 coils........

[KNIGHTRACE]

Glenfield well placed need a little humor on a Friday