Replacement CDI Unit

[Raceboy]

Originally Posted by Neil Harvey

This turned ugly quick.

This forum is for car owners who wish to do a lot of their own work, come on here for advice and knowledge. If we as pros wish to contribute, we should do so in the spirit of this forum.

Who cares what the scope traces look like, or how the ignition 'works". Really?

I'm a user of ignition just the same as the end user. I want something that is reliable and won't leave the owner stranded on the side of the road. If it gives some added benefits more the better.

I can understand the theory, but that should be for another forum. Where all "pointed headed geeks" can have their say. Here I believe if we wish to repair, sell or supply any part to the DIY community, it should be kept with the spirit of the forum and information given and not challenged in the open. We should be informative and as companies identify what the DIY owner actually needs in an ignition system. Is it because they want more power or is it because they want a unit that is reliable. I'll bet every penny for a dollar its the later.

Who cares if CDI is better than Inductive when it deteriorates down to the level this has gone. I can tell you we prefer CDI in the Porsche 911 engine with the hemi chamber. That does not mean that Inductive will not run the car. Our testing results are private and we do not throw them around in an effort to sell anything. When it comes down to "show me your dyno results or you are lying" the whole point of helping the DIY is lost. Get real, its not about dyno results but credibility, both product and company.

We test all products we sell and they all have to meet our quality standard. Both the units we sell do this in excess and both have their own advantages.

I have never had one customer call and ask, does your CDI unit make more power than this one? Show me your Dyno results? Everyone asks, is it reliable and will it leave me stranded. That you can take to the bank!!!!

This argument over CDI verse Inductive is never going to end. As a engine engineer (with a little experience) I can tell you both have their place. We use both. But one is better suited to certain applications in our opinion. That's it.

Are you serious?

I even did not ask for dyno sheets but your reasoning why CDI is better for 911 2v head. You do not answer but continue your talk with wall of text and still manage to actually say nothing.

And sorry, you are way wrong by stating that technical facts are not important. In a technical forum that is the main focus. For chit-chat there are other places.

With multiple sparks you try to overcome the most obvious shortcoming of CDI: extremely short spark duration and then it rises to level of inductive system when it comes doen to regular gas (not hard fuels like methanol or nitromethane).
Its ignition event last shorter time (0.5 ms) so if you don't light the mixture you'll get a misfire, but inductive ignition can take upto 2 ms which is much more likely to get it burning even if delayed.

BTW, if talking about reliability, then it is quite difficult to beat inductive system in that field. A 3-4 dollar IGBT with 400v internal clamp voltage provides up to 20A of current and lasts for decades without any problems. I still have ECU's running in cars that I tuned 12-13 years ago without any problems and several of those are more than 140 hp per cylinder (with turbo).

[Neil Harvey]

^^^
Are you serious?

Yes!!

You do not answer but continue your talk with wall of text and still manage to actually say nothing.

I've being accused of much worse.

[Jonny H]

Longer spark duration does not necessarily equate to 'better' igntion. The ability to ignite fuel has a lot to do with the temperature of the spark plasma. The temperature of the plasma is proportional to the power delivered to the spark plug.

When you compare the two systems in terms of power, the results are interesting.

Imagine an inductive system delivers, say 50mJ to the spark plug over a period of 2ms. If you remember your school Physics, Joules/second is in fact power, e.g. Watts, so the power of said inductive system is:

50mJ/2ms = 25 Watts

Consider the CDI system which might deliver only 10mJ to the plug but over a much shorter period of say 10us:

10mJ/10us = 1000 Watts

So, although short in duration, the CDI system has 40 times the power of the inductive system

If you think of the spark plasma as a heating element, It is obvious that it will get hotter with 1000W applied, rather than 50W.

The downside of the shorter period is you might 'miss' a pocket of highly turbulent air/fuel. This is what we address by delivering a second spark in a timely fashion.

[Raceboy]

Originally Posted by Jonny H

Longer spark duration does not necessarily equate to 'better' igntion. The ability to ignite fuel has a lot to do with the temperature of the spark plasma. The temperature of the plasma is proportional to the power delivered to the spark plug.

When you compare the two systems in terms of power, the results are interesting.

Imagine an inductive system delivers, say 50mJ to the spark plug over a period of 2ms. If you remember your school Physics, Joules/second is in fact power, e.g. Watts, so the power of said inductive system is:

50mJ/2ms = 25 Watts

Consider the CDI system which might deliver only 10mJ to the plug but over a much shorter period of say 10us:

10mJ/10us = 1000 Watts

So, although short in duration, the CDI system has 40 times the power of the inductive system

If you think of the spark plasma as a heating element, It is obvious that it will get hotter with 1000W applied, rather than 50W.

The downside of the shorter period is you might 'miss' a pocket of highly turbulent air/fuel. This is what we address by delivering a second spark in a timely fashion.

Yes, I remember school physics well and thank you for not just throwing nonsense but actually trying to explain.

I never argued that CDI would not have stronger spark vs inductive, I was arguing that when inductive system is up to its task (meaning no misfires) then there are no tangible benefits for end user. Also there is not just one inductive system, there are weak ones and there are very powerful ones.

Originally Posted by Neil Harvey

^^^

Yes!!

And still nothing. Is that also a secret why in your opinion would CDI be more beneficial in 911 2v engines?

[Jonny H]

The higher power delivered to the spark plasma by CDI, results in a larger ignition kernel and a faster flame front. This is particluarly beneficially in larger combustion chambers like the Porsche one, particularly when the fuel ratio cannot be accurately controlled by our ancient carburettors, MFI or CIS.

When you have a modern piston/chamber design and very accurate control over fuel (modern EFI), you don't need as much power to ignite the mixture, hence inductive in modern cars. Of course, this makes the engine more efficient as we all know every time we take our old cars to the filling station!

The Carrera 3.2 Motec ECU, allowed better control over fuel which in turn allowed and inductive system to be used. The main driver for this was emissions.

I don't dispute that if you changed the piston and head design, moved to a modern EFI, ran inductive etc, you would build a powerful and highly efficient engine. Just changing to an inductive system and leaving the fuel system alone? I doubt it.

An an aside, Neil is an engine builder so he is coming at this from a real world experience point of view. I think he has tried to convey that several times on this thread.

[Raceboy]

Thanks, I appreciate your explanation.

[Fred Winterburn]

A high energy inductive system can be very good, but to get the voltage control over a wide range of rpm and battery voltage isn't a whole lot easier than it is with CDI. Only modern inductive ignitions controlled by computers do this well. It's not as simple as varying the dwell. Sadly most CDI designs do not have much in the way of voltage control either(the old MSD 6A for example has no voltage control whatsoever) and it is essential to the longevity of the other high voltage components to prevent damage because of the high powers (watts) involved.
One aspect where there is no contest between the two ignition types, is in resistance to plug fouling, or shunt resistance. Once again it is the high power that makes a CDI nearly immune to plug fouling. The voltage rate-of-rise before breakdown does not slow down nearly as much with CDI compared to a high energy inductive ignition when faced with an alternate current path around the spark plug electrodes. That also reduces misfires. A few years ago when I installed one of my units on my brother in law's Fiat Spider, we finished up the job in a rainstorm. The spark plugs are recessed on that engine in little 'bathtubs.' The plugs were completely immersed in water on all 4 cylinders to the top of the insulators. The engine started and ran in CD mode, but when the switch on the CD box was selected back to STD, not one plug would fire. EDIT (I should qualify that although this comparison was to the original Kettering system which isn't that strong, I have tested much higher energy inductive systems and they do not fare much better against shunt resistance than the old Kettering system. Also the condenser in the Kettering system actually improves its ability to overcome shunt resistance to a minor extent) Fred

Originally Posted by Raceboy

Yes, I remember school physics well and thank you for not just throwing nonsense but actually trying to explain.

I never argued that CDI would not have stronger spark vs inductive, I was arguing that when inductive system is up to its task (meaning no misfires) then there are no tangible benefits for end user. Also there is not just one inductive system, there are weak ones and there are very powerful ones.




And still nothing. Is that also a secret why in your opinion would CDI be more beneficial in 911 2v engines?

[mysocal911]

Originally Posted by Jonny H

Longer spark duration does not necessarily equate to 'better' igntion. The ability to ignite fuel has a lot to do with the temperature of the spark plasma. The temperature of the plasma is proportional to the power delivered to the spark plug.

When you compare the two systems in terms of power, the results are interesting.

Imagine an inductive system delivers, say 50mJ to the spark plug over a period of 2ms. If you remember your school Physics, Joules/second is in fact power, e.g. Watts, so the power of said inductive system is:

50mJ/2ms = 25 Watts

Consider the CDI system which might deliver only 10mJ to the plug but over a much shorter period of say 10us:

10mJ/10us = 1000 Watts

So, although short in duration, the CDI system has 40 times the power of the inductive system

If you think of the spark plasma as a heating element, It is obvious that it will get hotter with 1000W applied, rather than 50W.

The downside of the shorter period is you might 'miss' a pocket of highly turbulent air/fuel. This is what we address by delivering a second spark in a timely fashion.

Using the same logic but for the 911 3.2 inductive discharge ignition:

1. The initial spark pulse per the scope trace, about 5us;



2. Total energy stored in the coil - 115mj (8 amps, 3.6 mh)

3. Assume just 10% of the energy used initially to initiate fuel charge burn - 12mj

4. With an initial spark pulse width of about 5us (scope trace) then;

Initial Spark Power = 12mj / 5us = 2400 Watts (2.4X the power of the CDI example)

The remaining energy in the coil (~ 100mj) continues to facilitate (over 1ms) the complete fuel charge burn. In the CDI system, the remaining majority of the energy is wasted, e.g. resistive
losses in the 'ringing', or returned to re-charge the capacitor.

[mysocal911]

Originally Posted by Jonny H

The higher power delivered to the spark plasma by CDI, results in a larger ignition kernel and a faster flame front. This is particluarly beneficially in larger combustion chambers like the Porsche one, particularly when the fuel ratio cannot be accurately controlled by our ancient carburettors, MFI or CIS.

Not really, as was just refuted in a previous post!

[Fred Winterburn]

Dave, That's an ugly waveform. The second spike looks like a restrike from a blown out spark which can happen with the remaining stored energy in the coil. Not a typical depiction that's for sure. Anyway, you are barking up the wrong tree again. I can take two almost identical looking voltage traces, one from an inductive spark breakdown, and another from CDI, and the CDI will have a much higher wattage. Fred

Originally Posted by mysocal911

Using the same logic but for the 911 3.2 inductive discharge ignition:

1. The initial spark pulse per the scope trace, about 5us;



2. Total energy stored in the coil - 115mj (8 amps, 3.6 mh)

3. Assume just 10% of the energy used initially to initiate fuel charge burn - 12mj

4. With an initial spark pulse width of about 5us (scope trace) then;

Initial Spark Power = 12mj / 5us = 2400 Watts (2.4X the power of the CDI example)

The remaining energy in the coil (~ 100mj) continues to facilitate (over 1ms) the complete fuel charge burn. In the CDI system, the remaining majority of the energy is wasted, e.g. resistive
losses in the 'ringing', or returned to re-charge the capacitor.

[RDM]

Jonny, Fred, Neil;

Thank you for continuing this discussion in the face of (or perhaps because of) the resistance you are getting. This is a feast for which I am thankful! Keep it coming

[Raceboy]

Originally Posted by RDM

Jonny, Fred, Neil;

Thank you for continuing this discussion in the face of (or perhaps because of) the resistance you are getting. This is a feast for which I am thankful! Keep it coming

I am sorry but to which questions Neil provided answers? I mean technical and straight questions? I did re-read it and did not find anything.

Only Fred and Jonny provided technical explanations.

Besides, after all that drama truth begins to uncover and even Jonny aknowledged that CDI is not necessarily the best choice in each application. And certainly not necessary in certain applications (which is what I emphasized already long time ago).
But I understand that my experience does not count for anything and every guy who has an opinion yet without any real knowledge in the field (engine control) knows for certain that I talk BS right?

[Neil Harvey]

Originally Posted by Raceboy

I am sorry but to which questions Neil provided answers? I mean technical and straight questions? I did re-read it and did not find anything.

Only Fred and Jonny provided technical explanations.

Besides, after all that drama truth begins to uncover and even Jonny aknowledged that CDI is not necessarily the best choice in each application. And certainly not necessary in certain applications (which is what I emphasized already long time ago).
But I understand that my experience does not count for anything and every guy who has an opinion yet without any real knowledge in the field (engine control) knows for certain that I talk BS right?

I guess you are questioning whether I know anything about ignition.

I have been doing performance work for a long time. If you want to check out my history there is a brief description of it on our web site, performancedevelopments.com – Engine Design. That will give you some idea of what I have done in the past and what I am involved with currently.

I started racing with carburetors and ignition points. We progressed to MFI and better distributors with reluctor pickups. Then we went through the magneto era and then EFI was born and we programmed with eeproms, programmers and calculators. In the 80’s we got PC based EFI and since then we have been programming with the latest systems by EFI Tech, Emtron, Link, Bosch, Magneti Marelli and McLaren. I think I have a “basic” understanding of how to tune an engine. It allows me to help others and the younger engineers coming up through the ranks to take over my job one day. Hopefully sooner than later!! This includes all engine calibration, Fuel, Ignition, boost control, traction, throttle control, engine/clutch control and the necessary engine function controls we are tasked to look after when our race customers use paddle shift gear boxes. Whew, I’m tired just thinking about it all.

I didn’t bother to write anything technical as Jonny and Fred have that covered. They are the real experts. They make ignition systems and parts and know way more about the techie stuff than I do. I just use the stuff. Do I know how it all works, what makes a good ignition and how combustion happens?

What I figured was what I could add, was my real life experiences with CDI and Inductive ignition used on Porsche 911 engines. In test we have conducted over the years, both on our engine dyno and in car testing we have found that CDI works best.
After all, more readers here want to know that stuff, not what’s inside the box to make it tick. Most have probably been put to sleep reading all c”””. I went to sleep and I’m interested in ignition.

We can read down to 0.5BHP on our engine dyno, so we can easily see what system produces more torque. But that is secondary in my opinion. Our in-car tests over the years with many different ignition systems have proven that our choice of product and the quality level we set was correct. I have not had one M&W unit returned for any sort of failure in over 20 years. I know Jonny’s product well now and I know it will equal the M&W product. This why we are now using it and carrying it to sell. It gives us options the M&W doesn’t.

In our testing with the 911 engine, we have not found one Inductive system with just about every quality coil made by man, to out-perform the CDI systems we use, both on the engine dyno and in the car. But the best statement I can make is the look on the face of the car owner when they drive their car for the first time with the new CDI. That is worth everything. And that’s where it really counts. Not this c””” we have served up for them to read.

I’m sorry you think I should back this up with dyno sheets or with technical jargon, I don’t want to and don’t have too. I rely upon my reputation to sell an idea or product and for the last 20+ years it has worked out ok for me and my company.

I can tell you what I have found but I cannot help you understand it. You’ll have to do that on your own.

[mysocal911]

Originally Posted by RDM

Jonny, Fred, Neil;

Thank you for continuing this discussion in the face of (or perhaps because of) the resistance you are getting. This is a feast for which I am thankful! Keep it coming

And what have you learned? You seem not to mention anything specific, like one unable to discern
what's really valid or not. Have you purchased one of the products (like M42Racer) being discussed
or are you considering such? You seem to just continue to post with platitudes without any specific
reference to technology or your Porsche/automotive experience.

[Raceboy]

Originally Posted by Neil Harvey

I guess you are questioning whether I know anything about ignition.

No, I was just indicating that instead of providing simple answers to my simple questions, you opted for long wall of text where you expressed your opinions but no technical explanation why do you think CDI is better for 911 2v.

I know Performance Developments (including one of your current projects in certain 944 Turbo).

[mysocal911]

Originally Posted by Neil Harvey

In our testing with the 911 engine, we have not found one Inductive system with just about every quality coil made by man, to out-perform the CDI systems we use, both on the engine dyno and in the car.

So you've tested at least one "Inductive system", as implied? Please indicate which one and
provide some comparative tech data, e.g. coil scope signals, dyno tests, type of engine,
carbs vs EFI, etc, versus a CDI system.

Thanks

[ian c2]

You’re mom goes to college .....

[RDM]

Dave/Loren,

Maybe you don't understand this, but nobody on this forum that you don't pay for needs to justify his participation at whatever level he chooses. Not the experts, and not those learning. I don't understand why you feel the need to demand answers from me. The platitudinous statements that I make don't cost you anything at all.

My feeling is that if your approach to the conversation here isn't similar to what you'd offer to your friends in your garage while sharing beer, you're doing it wrong. And if you talk this way to people in your garage, they won't be your friends. There is a way to ask questions that shows you are interested in understanding other people and respecting them rather than challenging them. I'm sure you know that.

I am learning things. Turn down your offense-o-meter, and maybe you will too. And maybe I'd invite you over for a beer.

Originally Posted by mysocal911

And what have you learned? You seem not to mention anything specific, like one unable to discern
what's really valid or not. Have you purchased one of the products (like M42Racer) being discussed
or are you considering such? You seem to just continue to post with platitudes without any specific
reference to technology or your Porsche/automotive experience.

[ian c2]

I was that drunk I didn’t even notice auto-correct had made me grammatically wrong .

[Jonny H]

Late night dyno session:

https://twitter.com/bsmotorsport/status/921133204718915584