EFI University

[APEX Speed Technology]

I've been tuning engines for 15 years now, and I've seen CDI ignition contribute to a number of improvements. Granted, I've had the luxury of working in fields where cost wasn't a big consideration, but quite often I've found more power and drivability from a switch to CDI. I'd like to discuss the merits of CDI and the arguments for and against it. For the purposes of this discussion, I would like to keep my assesments cost-independant. Here are a couple I've heard and read:

1. CDI spark's short duration is disadvantagous in certain situations. This is why MSD has "multiple discharge" CDIs.

MY TAKE ON THIS: Not valid if you tune correctly. The point of a spark is to initiate the flame front, not sustain it. If you are having problems doing this because of a short duration, you are running too much advance at low RPM. I feel this is backed up by the fact that all the multiple discharge units I know of switch to single spark at relatively low RPMs. I've worked on several offshore powerboats with large, cammy engines and crude intake tracts. Some have had Mercruiser's CDI, others had aftermarket 8 channel systems, and some had MSD CDIs. Most had distributors but 2 were fully sequential coil-near-plug. All of them were downright doicile at idle and low rpm - they have to be when you're trying to dock a 48ft cat.

2. FROM ELECRTOMOTIVE'S WEBSITE:
" According to the BOSCH automotive handbook 3rd edition...
Page 460... "The major advantage of the CDI is that it generally remains impervious to electrical shunts in the high voltage ignition circuit, especially those due to spark-plug contamination. For many applications the spark duration of 0.1 ... 0.3 ms is too brief to ensure that the air-fuel mixture will ignite reliably. Thus CDI is only designed for specific types of engine, and today its use is restricted to a few applications only, as transistorized ignition systems have virtually the same performance. CDI is not suited for aftermarket installations."

MY TAKE ON THIS: Plain untrue. A certain amount of activation energy is required to ignite a mixture. The activation energy of a combustible mixture is NOT time dependant. The reason it apears to be is that the longer time of an inductive spark means its more likely that the mixture nearest the spark plug will achieve a low enough activation energy. I did lots of work developing homogenous charge engine intake systems for emissions research applications, and I've seen how the instantaenous A/F at the plug changes quite a bit as the piston approaches TDC. Not to mention the effect of other properties including temperature and pressure. When ignition occurs as a result of a long-duration spark, you're effectively retarding timing. In reality, a properly timed CDI spark should never be "too brief" to ensure the air-fuel mixture will ignite reliably. And since the energy of a CDI spark is so much greater than inductive, a proper and complete burn is more likely to be established over a greater range A/F and cylinder pressures.

In the last year, there were several occasions where we converted cars with fully sequential coil-on-plug applications from Bosch multi-channel ignitors to both EFI and MOTEC CDIs. With no other optimization besides a larger spark plug gap, we saw peak torque and power climb 5-15%. Besides a more complete burn, I believe that a higher effective advance number contributed to the power gains.

But I continue to encounter engine builders who say there's no advantage. Any thoughts?
_________________
Neel Vasavada
Apex Speed Technology
2947 S. Sepulveda Blvd
Los Angeles, CA 90064
310-314-2005
www.apexspeedtech.com

[rotorhead]

Hi Neel,
Good to have you on board!
Im not sure if youve been reading the 'wasted spark' subject, but I have been on about the same. I am having trouble with inductive coil setups when tuning rotors and small 6 cyl turbo engines over about the 600 hp mark. I have been trying to ascertain what the difference is between inductive coils that are cheap and the higher end ones. I am definately in agreement that CDI would be better, because as soon as you are closing your plug gap you have issues in my book. This seems to be the only fix that I have come across or been told about. Unfortunately CDI is pretty rare in the 'import' scene in Oz due to everything being multi-coil so all these cars running GT40+ size turbo's are mostly running factory ignition systems with aftermarket computers. Could anyone tell me what a CDI setup is worth in the states? Do you still run wasted spark using standard inductive style setups (ie multichannel output from computer). Or does anyone know of an inductive coil that really grunts!

Cheers!
_________________
13BT RX3 sedan pure circuit (race)
13BT Courier Ute (work)
MY97 WRX Hatch (wife)
HSV TWR Group A Commodore 304 (show)
And now a Mazdaspeed 6 MPS

[EFIOZ]

Hey Neel,

We've seen the difference between a RACE1.9 (1.8?) on an F3 Mugen with and without the CDI. now this wasn;t a big rpm engine but it was a big comp engine (16:1 from memory). The torque gain around 4000-4500rpm with the CDi was quite noticeable, I'm guessing because at this point the cylinder filling is still high (the restrictor hasn't cut in yet) so the extra spark energy helps flame propogation. this would go with what you said about long duration spark retarding timing. The low speed driveability around the pits was also noticeably better. That was using the Bosch Motorsport coil on plugs with an EFI 4 channel CDI box.

We are about to convert the Renault engines in Car9 to CDI (should have done this when we swapped systems, doh!). So I'll report back after we've finished. Won't be for a couple of weeks as I'll be out of the country.

There does seem to be a very anti-CDI feeling amongst the Euro's especially. Maybe the all got burnt by the Might Spark Daily boxes of the 80's?
_________________

Competition Systems
Melbourne, Australia
www.compsystems.com.au

[APEX Speed Technology]

Two replies from Oz - anyone down there should definately look to Pat for his services. The guy is sharp, and doesn't mind taking EFI advice from the pub....

To address Rotorhead's questions: One possible difference between inductive coil design would be windings in the primary versus secondary. So you can get more spark energy with a bigger transformer (more windings), but its gonna take more time to charge and more time for the field to collapse (longer duration spark, but is it really more energy?) so what really is the net gain?

My guess (and this is only a guess, as one of my old engineering professors back in Wisconsin is probably having nightmares about me attempting to speak intelligently about this...) is that the main improvement between inductive coils is to have construction which improves the efficiency of the charge/discharge cycle. This is why that big 'ol Bosch Blue coil was such a hit in my MGB - all it had to do was improve on Lucas!

As far as CDI in Oz, don't ya'll have MOTEC and Autronic? I've good results with the MOTEC CDI-8 and EFI. Does anyone have comments about the MSD or AEM multi-channel systems? I've used both without problems but have heard mixed reviews from others. As far as coils go, as long as the ignitor's not build into the coil you're good to go with CDI. My personal fav are these little nippondenso deals but I'll leave it to someone else to disclose the source.

I have been following the wasted spark thread which is why I asked the CDI question. I very often run into engines where the ignition system is the limiting factor. I've seen many engines with sewer-pipe injectors (max duty cycle ~50%,) large turbos, and the stoutest mechanicals. Then they use an inducive wasted spark ignition setup, throwing away the stock coil-on-plugs for some 80's vintage NGK dual outputs and wires. Again, I work in a more costly world than the average guy on this list, but here is my take:

If you're going to spend more than $3000 on management, you should look past wasted spark or distributor-based ignition. There are plenty of boxes out there with enough drivers. If you're at the Autronic (for 4cyl), DTA PRO8, Motec M48 level, there's just no excuse not to. And don't even get me started about the M800s and EFI 2.1's I've seen running wasted spark. Doesn't make sense... unless you've got more than 8 cyl.

And while you're at it go CDI. Yes, its roughly $2500 additional investment. But it virtually takes ignition out of the equation.

And this is an open invitation for dissention, because I'd like to understand why so many people don't see the value in CDI. I'm not interested in being a snob and just calling them stupid.

-Neel
_________________
Neel Vasavada
Apex Speed Technology
2947 S. Sepulveda Blvd
Los Angeles, CA 90064
310-314-2005
www.apexspeedtech.com

[M_US_E30]

[EnzoFerrari]

Motec CDI8 is about $2500
Autronic 500R is about $900

I wouldn't use those $300 CDI's.

[EFIOZ]

EFI Technology CDI's

Single Channel USD695
Four Channel USD1495
Eight Channel USD2495
Ten Channel USD2995
SuperStock USD795 (Stand Alone unit with rev limiter and other goodies)
VR1 USD1495 (Retrofit for the old Lucas CDI boxes found mostly on Cosworth engines.)

http://www.efitechnology.com/documents/2004%20EFI%20Price%20Guide%20Rev%201.0%20web.pdf

The four channel with the twin output Denso coils works a treat on big HP V8's. Although I agree with Neel in that if you've got the drivers, use them. Plug top coils from Denso and Marelli are also top notch and not overly expensive.

Another adavntage we've found is the ability to still have good spark at low battery voltages. A huge bonus for race cars with total loss battery systems or when an alternator goes down on you. I think most ECU's will give out before the CDI does.

http://www.compsystems.com.au/tn010804.htm
_________________

Competition Systems
Melbourne, Australia
www.compsystems.com.au

[Geoffrey]

Neel,

Good to have you on board. As mentioned in the "Wasted Spark" thread, I believe that ignition system design is one of the most misunderstood subsystems of an engine. I say this because you may have one that is functioning, but not functioning optimally. How can you tell without measuring it on a dyno?

With regard to your question on MSD, I have not had good luck with the MSD DIS-4 systems and have seen benefit moving to an Autronic R500. Also, as you mentioned coil construction is important and can make a large difference in performance whether you are speaking drivability or peak power.

I will say that I recently read an article that spoke of F1 ignition systems and they said that of the teams, 1/2 are running CDI and 1/2 are running Inductive so I have to believe there is more to it than the level we are speaking. However, I believe that in general, if you replace an OEM type ignition system with a good aftermarket CDI unit, you will see and feel improvements.

FWIW, Electomotive uses an ignition system designed by GM from the mid 80s. I believe that there are much better choices of inductive systems out there today.

Here is a scenario that I'd like to better understand. On a factory Porsche 964, 993 street engine, and 964/993 RSR race engine, they use a simple Bosch ignitor, coil, and twin distributor. This means that at redline of 8000rpm there is 7.5ms of time for 1 crank revolution, and there are 3 ignition events within that time, or 2.5ms available for coil charge time. Now, we know that the coils that are on that car require about 3.0-3.2ms of dwell to be fully charged. Sooo, what do we have here? Porsche isn't dumb, Bosch isn't dumb, why would this design be used, or more importantly, be used in a racing application? Perhaps it was rules that required race systems to be the same as street systems, I don't know. But at the end of the day, it APPEARS that the coils are not fully charged when the engine is operating over about 6000rpm on either race or street version!

For CDI components, you may want to check out components from M&W Ignitions in Austrailia along with MoTeC, and Autronics. I believe they are the manufacturer of MoTeC branded 1,2,3 channel CDI units. They also have a good selection of well designed coils that I've used with the Autronic R500 with good success.
_________________
Racetek Engineering
93 C2/RSR
89 930
91 944S2 Club Sport
87 924S

[APEX Speed Technology]

[efiguy]

"I'm wondering, what are the availible triggering methods for the Autoronic and M&W? Can it be easily integrated to a MOTEC M800, EFI Race 4.0, or Bosch MS 4.1?"

These ignition units typically require a falling edge trigger, so as long as the ecu's have flexible trigger outputs and you can set it for a falling edge its all good.

"How robust is the Autronic, MSD and M&W hardware? Has anyone experienced failures which were confirmed as hardware?"

So far so good. I have had extremely good luck with both of them. I have seen only one failure an an R500 Autonic unit that was severly overheated......it had a high boost misfire, but since then I believe the problem was addressed and I haven't seen it since.

Another issue that is interesting, is why do some EFI systems allow programmable dwell timing based on RPM? How is the total time available in an engine cycle related to the amount of time it takes to charge a coil?

Even at the top of our field, we have much to learn.
_________________
Setting the Standard

[Geoffrey]

Both the M&W and Autronics trigger on a square wave output so you shouldn't have any issues there.

On the 993 RSRs, GT2, GT1s that I assume you're talking about, did they convert to direct ignition or continue to use distributors? I'd be interested to know how they handle the requirement for twin plug which is one of the most difficult aspects of ignition on a 911 engine, especially if direct ignition is used.

The new GT3 Cup and GT3RSRs continue to use inductive ignition with small coil on plug packages. These normally require higher dwell time, for instance, the Denso 580 (LS1/LS6 Corvette) require 5.8ms of dwell. I wonder what the alternatives are for an application like this.

I looked for the article regarding F1 cars which I thought was in the technical analysis book from 02/03 season, but couldn't find it. It may be in my stack of Racecar Engineering magazines which I'll never find.
_________________
Racetek Engineering
93 C2/RSR
89 930
91 944S2 Club Sport
87 924S

[APEX Speed Technology]

[Geoffrey]

It is frustrating to not understand and to not have connections to the people who do know.

I have been told that you cannot/should not run CDI with double ended coils. The first experience with that was a shop that put a single MSD DIS-4 connected to 2 Electromotive double ended coil packs. So what you have is an ignition system that has to fire 2 spark plugs with a mixture, and 2 spark plugs on the exhaust stroke. It ran, but eventually burned up the coils. I've since replaced the inductive Electromotive coils with M&W double ended coils designed to run with either CDI or Inductive ignition (so I guess they think you can) and connected it to an Autronic R500 which has a high power setting that produces about twice the output as the DIS-4. I've yet to try it, but others that have indicate a much better performing ignition system. The original system would misfire at a plug gap greater than .020" and 1bar of boost.

The MoTeC can produce a trigger that is on the falling or rising edge, and is 12v. I know the Haltech systems can also do that as can Autronic.

The Porsche GT1 was the water cooled twin turbo engine in the mid engine chassis in 96-98 and I believe ran Tag Electronics in it. I've done some work on the Cup car engine and assisted a shop tuning one converted to twin turbo. Too bad it didn't have a real ECU like MoTeC in it though

Coil near plug is interesting for packaging, but there is limited space for substantial coils so I'm not surprised that they may not perform very well.
_________________
Racetek Engineering
93 C2/RSR
89 930
91 944S2 Club Sport
87 924S

[efiguy]

"Which systems are these? Do they also have a dwell correction for battery voltage? Why would you want to charge a coil any less than maximum, and if you're out of time at high rpm, why wouldn't you charge it until you have to collapse the field? Good question..."

Well, I guess its not really fair to say "some systems", when I really mean that Autronics can do it. I have placed a call to Australia to see what I can learn, but for now there must be more than meets the eye here.

The way I see it, we should be able to take a look at the scope and watch the rise in voltage vs. time across the coil and thats simply what the dwell time is. The Autronic systems allow you to program this time in a 3D table where battery voltage is on the vertical axis and RPM is on the horizontal. I can't imagine that a guy like Richard Aubert would go to all the trouble of writing it into the software just for the excercise. There must be a reason????

"What are the exact specs on this? 0-5V? 0-10V? Do they trigger on the rising edge? Just curious."

The R500 CDI can trigger off of just about any trigger source voltage above about 4 volts, as long as it pulls down below .7 volts. This means you really don't even need to go all the way down to zero or ground, just give it a wide enough window and it'll sort out the rest.

"I bench tested those LS1/LS6 Corvette coils and was almost shocked at how poor they perfromed. I guess they figure its not the most streesed ignition system, so its no big deal. Coil-near-plug and all is great, but with a base dwell time TWICE that of a decent Denso single output?"

I have never liked those goofy things with the inverted dwell signal. Plus they are about as ugly as you can possibly make a coil.

"I've not done any management work with the new Cup cars or RSRs since the Bosch MS ECU does a pretty good job and that's what PMSNA supports. No one ever complained, even with the pretty hopped up ones Kelly Moss ran in some of their GT3Rs last year. Would someone in Grand Am, ALMS or World Challenge would step up and do some electronics work on those motors? Does anyone other than PMSNA build those motors for pro-racing? Would PMSNA be interested in trying something else/ I'd wonder if a better ignition would help those motors on the top end, especially if they have long dwell times. Then again, I've heard that they're having a hard time handling revs anyway, so maybe that's not a really good answer. Take all this with a grain of salt, I know nothing about anything really..."

I nearly became a distributor for Bosch Motorsports a few years ago, and they are very nice ECU's but not very flexible. You must use 60-2 trigger patterns, and they are purely inductive ignitions, although I suspect you could simply turn the dwell period way down and just use it to trigger a CDI without too much problem.

The real thing that killed the deal though, was that PMSNA has a password protected version of the MS3.3 ECU's that they use and they also have a specially pinned wire loom that moves certain pin locations around strategically to prevent someone from using a NON-PMSNA MS3.3 to run the car. Apparently Porsche is very closely tied to bosch Msport and the porsche club racer crowd was going to be my target market. In the end, I found that it was too expensive to be so unflexible and would rather spend the money on EFI Tech, Autronic, or Brand M.
{sorry Geoffrey}
_________________
Setting the Standard

[APEX Speed Technology]

[efiguy]

[EFIOZ]

[EFIOZ]

[Geoffrey]

[APEX Speed Technology]

First off all, thank Geoffrey for the education in all the cars/ECUs. I know I need to be able to keep all the chassis designators and ECU models straight; its good to know them all for future reference. In an earlier post I talked about a GT1, I apologise but that as an RSR.