What coils did you use? Dual post? Where and how did you mount them?

 

Why would you go to the trouble to run the fuel sequentially and not the Ignition as well. If your going to mount 2 coils, how much extra trouble would it be to mount 2 more. I have seen the coils mounted on the Valve Cover. The hood clears. You would be better to run the Distributor along with the sequential fuel and then everyting is clean and simple. There is the question of accuracy with the Timing belt, but for the street, I would think the difference is very small indeed. There is the thought that the timing belt has a dampening effect, where the Crank trigger is also affected by Crankshaft torsional twist and vibrations. Either way, makes little to no difference in the real world, but on paper makes for great reading.

 

Accel, MSD, Nippon-Denso all make good dual-output coils for EFI systems. With the low redline of our cars and low cylinder count, a single coil is never taxed to the point where its output is compromised. As M42racer mentioned, a distributor set-up would work just fine. In fact, you end up with double the output because all the energy of the coil goes to a single plug, rather than being spread between two plugs as in wasted-spark (hence the term wasted-spark).

Actually most of the energy in wasted spark goes through the plug on the exhaust stroke because the gasses there are easier to jump than the cylinder on the compression-stroke. If you're gonna do dual-output coils and sequential ignition, I would get a CDI system, rather than inductive.

Anyway, I can get you a distributor-cover that plugs up the hole in front once you remove the cap and it has a shelf to mount two dual-output coils. That way, you can still use the stock plug-wires.

BTW- on high-revving 8000rpm Miata engines, a lot of people have had a lot of issues with spark-scatter due to the cam-pickup being out of phase with the crank due to timing-belt oscillations. Do a search on that and you'll find the relevant info.

 

Changing over to CDI is the best kept secret there is. When its done, the real power is unleashed. There was no power objective when Inductive was introduced. Cost, less Rf interference and longer spark duration for better emissions were the goals. Change over to a CDI and you will feel the difference.

 

Could someone explain explain with hand puppets the difference?

 

Dan,

Doesn't the TEC3 use a wasted spark set up? The Electromotive site states:

"Unlike multi-spark CD systems that from around 3000 RPM just give you a single very short duration spark, Electromotive puts a full 150mJ of spark energy to the plugs with a spark duration more than ten times the duration of a CD spark from idle to 9600 RPM. This long duration spark makes more power!"...

By using an Ignition Coil for every pair of companion Cylinders, the TIME available to CHARGE an Ignition coil goes up by a factor of 4 on an 8cyl Engine. This allows you to use the advantages inherent in an INDUCTIVE SPARK... this uses only enough voltage to ARC the gap of the Spark Plug and dissipates the rest of the SPARK ENERGY in DURATION ! up to over 2 Milliseconds

If I'm understanding Electromotive's descriptions, CD ignition systems are inferior to their Direct Ignition (wasted spark?) system because the spark energy from a CDI's is much less and the spark duration is also less. Am I reading this right?

Just so I understand, a CDI setup on the 951 requires 4 coils and a trigger wheel on the cam sprocket to have a fully sequential ignition? And like M42 said, does having a fully sequential fuel and ignition system represents the greatest power gains compared to wasted spark or inductive systems?

 

I have been running a full sequential wasted spark set up for a couple of years (Electromotive Tec3).
It works well……
The coil pack is mounted on a bracket that I make up for this specific application (944 turbo)
Any particular questions?

Chris White

 

My initail point was why? If you go to the trouble of running sequentially on the fuel, why would you not run the ignition like wise. I understand why the electromotive system is wasted spark. They sell their system with those Delco Coil packs which are Dual type coils which can only run as a wasted system.

The advantage of some EFI systems over others is that you have the choice of how to run the fuel and Ignition. It all comes down to your particular needs and compromises. There are huge advantages in CDI verses Inductive. Forget what is written in sales ads, there are 2 formula's which define the difference.

I have copied,

Inductive equation is

W = 1/2LI* where I is squared.
W = Energy (Joules)
L= Primary inductance (Henries)
I= Primary current (Amps)

CDI equation

W= 1/2CV* where V is squared
W= Energy (Joules)
C= Capacitance (Farads)
V= Voltage

In a standard inductive Ignition system all the spark energy is stored within the magnetic field of the coil and is defined by the Inductive equation.
A typical modern coil used with an electronic ignition has a primary resistance of 0.5Ohms and a primary inductance of 3mH. If this coil is driven to a primary current of 6A it will give a max spark energy of 63mJ and require a min of 3msecs to recharge (dwell) bewteen events. The energy figure can be raised by either increasing the primary current or primary inductance, however this also increases the dwell time and there by reduces the engine speed at which the saprk energy begins to fall.
If you look at a V8 engine with the Inductive equation, the max spark energy would be available up to 5000RPM, and from there begin to decrease.
In a CDI system, 12V is stepped up by inverting the power supply to 450V which is then stored in the capacitor.
If a 0.5uF capacitor is charged to 450V, the max energy would be 100mJ. the efficency of the inverted supply can recharge the capacitor within 1 msec giving a max ignition fequency of 1000Hz or 15,000 RPM without any loss of energy.
The other advantage is the high rate at which the secondary voltage rises, which gives the CDI system the ability to fire a plug under conditions an Inductive system of eqaul energy cannot. Fouled plugs will never be fired bu an Inductive system, where as a CDI system will typically burn off the dirt and fire the plug.

These are the main differences, and most high perfromance systems are CDI based. Inductive systems are typicallly OEM, where lower cost, non Inference of other electronic systems are all factors which play into the use of Inductive systems.
Which is better, it all comes down to your requirements. If lowering your costs is important over function, then go Inductive. If function and Ignition power is # 1 , then go CDI. Multi channel CDI units become very expensive, and is the main reason why many use inductive over CDI. If your system is a single channel system, 944 with distributor, the CDI will out perfrom the inductive system. Most EFI systems will drive either types, (EFI TECH, MOTEC, LINK), its only a wiring change
required. The systems which do not allow either type of Ignition, Electromotive and some others do so to allow multichannel systems at a lower cost where no distributor is used. These systems offer only wasted spark systems in order to keep the costs down. Any time a CDI system replaces these types of systems, noticable idle, power differences are felt.
There are many types of CDI units available, some with more energy than others. Most typical is around 108mJ, but some offer up to and over 150mJ. Whatever the claims are of the Inductive systems, the spark energy can never compete with a CDI system. Multi spark events are only up to a certain low RPM, all trying to help with the idle, clean burn etc. Any single hard spark will always outperfrom this feature. Its great marketing.
When choosing a system for the 944 application, the use of Inductive is most common to lower the price, and as the RPM limit is low, the decrease in spark energy is minimal. However, as Inductive has a lower energy per RPM, the use of wasted spark should be considered only when full understanding is known. The coil energy is 1/2 as it is shared between 2 plugs. This is why resistor wire/ plugs have to be used with wasted spark, to try to balance out the spark energy at the plug on compression along with the plug on overlap. So, whatever the coil energy is, the energy at the plug will always be 1/2 approx. In the real world, the energy at the plug on compression is less than 1/2.
So, this is why for 944T applications, the best system would be a sequential 4 coil system, using a 4 channel CDI unit with CDI ferrite coils. Lots of $. The next best system would be 1 channel CDI using the Distributor. 3rd would be close, CDI with wasted spark or Inductive thro the Distributor. The math would have to be done here to see what the energy levels would be. And last would be Inductive in wasted spark. The last choice is always because of cost, never for best perfromance.
The above formula's and info are from repected Ignition companies. I know the Link system offered for the 944 application can go either way, and the typical system offered is single channel Inductive used with a distributor. I know some have purchased the single channel CDI unit and these run very well. To have multicoil applications (sequential)with any system, a cam sync must be used. The electromotive systems use a 58 tooth crank wheel with a sync (the 2 missing) to establish TDC, but not # 1 TDC compression, but #1 TDC on both strokes. This is why a cam sync must be used to establish #1 TDC compression. Even the use of the factory Crank triggers,(Link) will give both TDC's. The cam wheel that Link offers gives both the sync and full triggering, thus allowing this triggering to be the only one needed.
There are noticable effects of wasted spark. The most typical is all the "popping" under decel, which is the firing of the plug on overlap. This is acceptable by most, but is a waste of coil energy, and at times on the street brings the wrong type of attention.
I hope this has answered some of the questions, and in no way am I endorsing any system over another, but hopefully explaining the differences and secrets of the many systems available.

 

I am pretty ignorant to the intricacies of ignition systems. What exactly are the options and benefits presented to someone that might go down the standalone ecu path?

1. Batch/sequential?
2. Capacative/Inductive?
3. Wasted Spark...Coil pack?
4. Distributorless?

Is the TEC3 system a compromise? It is distributorless but it is still inductive...is that correct? What about a setup like the MSD 6A...that is CDI, right? Can that be utilized with a Link2?

Max

 

Hmmm…I must be in the right mood, I usually don’t bother with this stuff –
If you are so inclined the Electromotive system can run ‘full sequential’ for spark – 1 coil per cylinder and it might add $100 to the price tag. You don’t need it so don’t bother.
What’s the most important aspect of an ignition system? Correct timing. That’s it – pretty simple. If you have enough spark energy to fire the plugs what’s the point in adding more? If you are having a problem firing your plugs with the stock system then look for something to fix as opposed to just adding more ‘power’ to your spark.

Its about accuracy. A degree matters here….alot! (Electromotive is accurate to ¼ degree under all circumstances)

Cam mounted triggers are fairly bad when it comes to absolute accuracy.

BTW – if your wasted spark engine* is ‘poping’ under deceleration then you don’t know how to set up the software. (*- Tec3 based).

“I hope this has answered some of the questions, and in no way am I endorsing any system over another, but hopefully explaining the differences and secrets of the many systems available”

Um, OK….sure.

I have nothing against the concept of CDI but to actually believe that power is more important than accuracy is heading way down the wrong road. If you feel the need for more than 150mj then go ahead, the only reason I can come up with is your engine is either way out of tune or you can’t pick the right plug.

Sorry to be so harsh, I didn’t have any issue with your post until you got to the point on how great the cam trigger was and that the combination of the cam trigger with the Link and CDI was the best thing since sliced bread. Wrong.

 

Hey Chris, so the TEC3, using its inductive coil packs and crank trigger wheel provides better better ignition accuracy and that is its primary advantage? Is this an advantage the TEC3 has over other standalones or an advantage of inductive coil packs in general?

Max

 

Mr White,
Whoa! Must have touched a nerve. Never did I wish to wrong any system or your choices. Nor did I say that the Cam triggering with the Link was superior. Just that it is offered and can do all the triggering.
If I may offer a retort to some of your points, I differ as do most Ignition experts I have consulted here, before posting what I said.

You state the Electromotive can run sequential. My mistake. Very good, we have another choice to choose from. After all, its all about choices.
As for the increase in price, I have no idea what this system costs, but to run multi coil in sequentail mode and only adding $ 100.00 to the users costs seems a little low. Is there a cam sync and Igniters and coils that only increase the bill by $ 100.00. Thats great if there is. Again, the customer wins here.
The accuracy as you state is very important. The factory uses 132 teeth to measure the accuracy. Mosts systems then use the tooth count and re math this to get the triggering count they need for their software. Any Cam trigger that is driven via a belt must be less accurate, but within the concept required for these engines, RPM etc, it is a good alternative when wanting both sync and triggering. If absolute accuracy is required, then use the crank and add only the cam as a single sync. As I stated, it all comes down to cost and what compromises you are prepared to make in order to get what you will accept. As for 1/4 of a deg accuarcy on your typical 944 application, thats a other post altogether. What I understand people want is the ability to change the timing, be accurate with it, and argue over the decimal point last. For a typical 944 application Mr White, I'm sure you would agree thats a little over the top. For most, running 2 degrees away from knock would be safe, right?
My post was not about timing accuracy, but the differences between Inductive and CDI ignition systems. Whether you have 1/4 deg accuracy or not, the conditions of CDI verses Inductive still remain.

I have re read the rest of your post and cannot understand the points. Spark energy does make power. You always want as much as you can get. Ever tried to fire a fouled plug, tried to fire a plug with very high in cylinder pressures? Pretty typical in Turbocharged engines. Not sure I understand your point here. Seems a little general. I tried to offer specifics and points of difference. You have offered, if you can fire your plug, why have more? I THOUGHT MY POST WENT INTO SOME DETAIL WHY? Do some math and you will see the exact reasons why. Its not my opinion, nor am I an expert. Its basic electronics. Spark plug choice is a constant. The same plug, with the same gap, will not add any energy. The heat range makers no difference. The gap does. And under boosted conditions, some gaps are too large for the Ignition system to handle, thus requireing less gap. Typically CDI systems will jump very large gaps Inductive systems will not. Larger gaps typically will produce more power. Projected plugs where Piston clearance and in cylinder temerature allows will help produce more power. The CDI systems will help fire these plugs with gaps Inductive systems would struggle with. In most turbo cases projected plugs need to be colder, as plug temperatures get higher. The projected part of the Plug is exposed and removing the heat is paramount.

As for the rest of your post, you have come to conclusions here not from my post, but from your own. You are obviously a electromotive dealer. Thats great. every one has their reasons and choices. Its was never my intention to demean any system, just to point out the differences in Ignition types, not EFI types. I mentioned several EFI types I was aware offered the ability to run sequentially, I was unaware the electromotive did also. My mistake. You learn something everyday, right.
Your point about accuracy is a good one. My post was never about this. It was about spark energy, the differences between Inductive and CDI, choices that are offered and how they relate to the 944 application. Many choices involve a compromise. As for the need for more spark energy, I have never seen an application where to much was a bad thing. Its like Water Pumps. You can never have too much.

 

Good discussion guys...lets not get pissed.

So M42, you are asserting that applying the greatest spark power is the ultimate ignition goal (assuming the ignition is adequately accurate and precise)? And CDI is the best way to do this? Are there any factory cars that do this? Any factory race cars?

Max

 

Agreed. lets not take it to heart.

Most factory cars today if not all use inductive for several reasons. Cost, Inductive is a lot less $ for multicoil applications, RF Interference is a lot less and most cars today have many electronic components which can be interferred with by RF noise. The better CDI systems have noise reduction built into them, but CDI systems in general produce more noise than Inductive. As for race cars, I have no idea. The Porsche GT3 cars are all inductive, for the above reasons. As for others, I have no knowledge. What I do know is the top EFI companies other than factory, offer CDI over Inductive. What is used in the very highest form of racing. I have no idea. Whatever it is , it would be extremely expensive. At 19,000 RPM, the ignition required would be very special. As for the ultimate Ignition goal, I assert that CDI will always out perfrom Inductive given all things been equal. As for the ultimate goal, that comes down to the goals set forth by the user I would think. As for the best way to do this, again the goals of the user, the compromises etc that need to be taken into consideration, all factor into the best way. If cost is important, and you want multicoil Ignition, then you will have no choice but to use Inductive. Then what was the best solution, well it became simple, as the cost of multi channel CDI's are up to and well over $ 1000.00 ea depending on how many channels we are talking about.

 

Is it advisable to use a cam trigger wheel on our cars? Doesn't the rubber timing belt represent potential discrepancies due to belt stretch?