Amen!

WOW just WoW
This is a car forum where car guys talk about horse power, building engines, hot chicks and the smell of race fuel in the morning. Where bragging about your last monster build is regular fair.
Since when did everyone get so sensitive.
Next thing you know, swear words and girly posters will be banned from the garage.

Every one of you has had a more heated discussion over turkey dinner......

hey, seeing as all the brightest minds are in this thread, reckon you could have a squiz at this for me ....
https://forums.pelicanparts.com/911-engine-rebuilding-forum/1084339-another-964-through-bolt-question-o-rings.html#post11221493

So I have a question about this discussion, but it would seem to be in "reverse" fashion because I think, but i'm not certain, i'm thinking about an inductive ignition with two coils and one ignitor.

I believe both Jeff Alton and Neil Harvey mentioned in this discussion here that running two coils from one ignitor doesn't go well. Neil mentioned the ignitor tends to overheat and that's why a conductive paste is used to transfer the heat to a sink. I've seen this ignitor and conductive paste design in a Mitusbishi 2.0L 4 cyl. turbo ignition (distributorless and multiple coils) and a 1980s GM HEI TPI V8 ignition (single coil). I openly admit that this is bringing up more old technology inductive stuff and that does not imply i'm trying say it's great, nor am I trying to crap on it. Reason I ask is because it then made me think of the 993 ignition. Aren't the two coils fired by one ignitor the way a 993 twin ignition is arranged? I know for certain it is unlike the 964 setup with two ignitors. I also see Steve Wong has developed an alternative to the famous Andial signal splitter by modifying the Motronic ECU and incorporating a single 993 ignitor


911Chips.com - Porsche 911 Performance Engine Components

I'm not trying to say that if the 993 has such an ignition, it must be great. My question is actually, is this approach inherently flawed because it employs an overworked ignitor with a conductive paste + sink. It would appear the paste & sink are a compensator for the shortcoming of too much heat?

Please know that I don't mention Jeff and Neil to call them out. I totally respect their knowledge and input here, and i'm not questioning if they were wrong. I'm just trying to see if I correctly understand what they said. Their mention of the ignitors triggered (pun intended) my memory of the ignitions I have encountered on previous cars of mine and then I thought of the 993 setup, which is sort of pertinent to the conversation. Is one ignitor for two coils the inductive version of using one CDI to fire two coils?

Kevin,

Against my better my better judgement I am posting again on this thread.... I am fine with having to block some members... lol

It is pretty simple. There are those who build engines and test our results (regardless if they could be better) and then there are those that build and have results that are good and meet their needs and then there are those that read what other's post, ask questions and create an "informed" opinion. There is room for everyone to post on these topics, and in fact each post can add value to the discussion. Regardless of the experience of the poster.

I hope to not get into anymore debates with those that have no actual experience building and testing engine combinations. That does not mean we think we are right. It only means we have data that backs up what we do, regardless of whether it conflicts with what other folk's data that is based on a white paper or is based on "What they heard". William, Henry, Neil etc and any one else with true experience are who to listen to and would exchange ideas with to perfect our craft. We are always in a state of learning, if we were not we would be standing still at best. We value the input of those with far more experience than we have to the 10th power, even if we disagree or question them at times.

On our Twin Plug builds using 12 COPs with AEM Infinity ECU we are using 2 ignitors. I don't think we are down any power (though maybe we are?). Happy to be proven wrong. I can (RE) post the dyno sheets of a 3.8, a 3.4 and a 3.2SS again but not interested in the feedback from those who don't know what they are looking at and have zero experience in building performance 911 engines..... (I don't mean you by any sense). Forget the numbers on the sheets (it is not my dyno) but look at the curves and ask one's self if more HP is on the table in terms of ignition capability....

Again, I am open to this great dialogue. We always learn something in these friendly debates. If we were building a twin plugged carb motor with a 964/jarvis/jb/superterch or whatever distributor we would be asking questions of those that have actually done it. We only offer our experience to the board where we have actual experience.

And yes HENRY, you are quite right. None of this is worth getting butt hurt about. My goodness. This is a forum for enthusiasts looking to learn and offer experiences. Be it professional, hobbyist or clueless. We all learned somewhere. Just because someone with a "username" didn't agree with us should have no bearing on how we feel or how we react to posts. But it really is not a place for people who have no experience to post as someone with experience. By all means post what you heard or talked about with person X, we can all use that information.

This is the engine rebuilding forum after all, right? AMEN to you Henry, brother.

Kevin,

It isn’t the number of igniters.....it is the number of channels per igniter.

My race engine has 4 3-channel igniters so each of the 12 CoP sticks has its own channel.

The Bosch 0-227-100-200 used in the 993 is a 2 channel igniter designed to handle 2 coils.

http://forums.pelicanparts.com/uploa...1613206712.png

Kevin,

The Bosch 0 227 100 124 igniter has a single channel and there are 2, one for each coil, used in the 964.

HI Kevin,
This is a long answer to your question but hopefully clears some things up.

Is one ignitor for two coils the inductive version of using one CDI to fire two coils?

Not really. If we think of the most basic inductive ignition it has points and a coil. When the points are closed electric current flows into the coil. When they open the field falls and you get a spark. The limit of this design is how much current you can run thru the points without burning them up. Plus points require constant adjustment.
Many manufacturers switched to “transistorized ignition”. This changed the system so that the current flows thru a transistor. The amount of current is only limited by the size of the transistor. A transistor is just a electrically controlled switch. The on/off “trigger” for the transistor can be multiple things. For some ignitions there is a optical or magnetic “trigger” built into the distributor. For most later cars this trigger signal comes from the ECU.
An ignitor is just a transistor or group of transistors with each channel being a transistor. The important thing is that the transistor in the ignitor needs to be able to handle the amount of current going to the coil.
Bosch 0-227-100-200 used in the 993 is a two channel ignitor. I could not find the specs on that unit to use as an example, but I could for the 227-100-203 from Bosch motor sports referenced on Steve Wongs site (911chips).

Full specs here.

https://www.bosch-motorsport.com/content/downloads/Raceparts/Resources/pdf/Data%20Sheet_68570379_Ignition_Module_IM_3.2.pdf

The 227-100-203 is a three channel ignitor. The maximum recommended current for each channel (transistor) is 10Amps. If we look at the recommended coils for this ignitor the p50 is listed as a recommended coil.

Looking at the P50 coil (full specs below) technical specifications we see that the current for that coil is 5-10Amps which matches with the ignitor max of 10amps.

https://www.bosch-motorsport.com/content/downloads/Raceparts/en-GB/50280203208699019.html#/Tabs=50291595/

However if we look at the C90i coil which is a high power coil (90Mj vs 50Mj) we see from its specs that the current for this coil is 10-20Amps. This is more current than the 227-100-203 is rated for and the transistors would most likely overheat and fail.

Its also interesting to note that the 227-100-203 is rated up to 8000RPM.

So for the inductive ignition using two p50 coils and a single ignitor with a rating of 20 amps or a two channel ignitor with each channel rated at 10 amps the result would be approximately the same as there would be sufficient current capability from the ignitor for both coils in both cases.
So its about matching the parts to the application.

The CD ignition works different than inductive. The CD ignition first raises the voltage to several hundred volts and charges capacitors (capacitors work kind of like batteries that can release energy very fast). When the ignition signal is sent to the CD box (instead of ignitor) it connects the capacitors to the coil (probably thru a transistor). The other side of the coil is connected to the other side of capacitors and capacitors release their energy into the coil.

For the CD ignition with one coil vs one CD with two coils the two coils will have approximately half the energy and half the spark time. This is because the two coils will drain the capacitors in the CD ignition in half the time and the energy from the capacitors will be split between the two coils so half the energy output.

Just like inductive ignition the components need to be sized to the system so do CD. By changing the coil specs and CD specs you can affect the amount of energy and time of the generated spark.

Since specification for standard OEM automotive parts can be difficult for the public to come by the learned experience of those who have tested by trial and error of what works is often the best guide for making choices.


john

Nothing like having an EE explain things. I'm glad I kept reading this, because I hadn't realized that CDs fired when the coil voltage input happened, rather than when it was grounded and the field collapsed.

The documentation for the Bosch 227-100-203 says the following:

"This module is an external ignition power stage capable of supplying up to three non-transistorized ignition coils."

https://www.bosch-motorsport.com/content/downloads/Raceparts/Resources/pdf/Data%20Sheet_68570379_Ignition_Module_IM_3.2.pdf

It seems Bosch does not intend a single ignitor channel to drive more than 1 coil.

The Bosch 227-100-200 module appears to have the same specs as the Bosch 227-100-203 module:

https://www.pim-engineering.com/tiedostot/ignitionmodules.pdf

You certainly would not want to drive two coils per channel with any of these Bosch igniters.

Thanks to Scott and John for the detailed information on the Porsche/Bosch ignition modules. I appreciate the technical insight as to how these modules are designed to work

Jeff,

What brand and model igniters are you using?

Jeff,

If you are using the AEM 3 channel igniters, I asked AEM about using just two of those on a 12 CoP Porsche dual plug six cylinder setup. Here is what they said:

"We do recommend running four of the 3CH Coil Drivers for this specific
setup. Triggering two coils on a single channel will cause the igniter to
overheat and fail.”

If you are using two 6 channel igniters, great. AEM doesn’t make anything like that though. I think Haltech does.

Looking around at all of the igniters I find people might use in street builds, none have enough current handling capacity on a channel to drive two standard ~10 amp coils. I certainly can't find any documentations from any igniter manufacturer saying it is okay to use 2 coils on a single igniter channel.

The higher performance igniters that I did find that support more current on a channel are designed and intended to be used with higher current coils. So again, a single coil per igniter channel.

Based on this, and the fact that a CDI system using 2 two coils on a single ignition has half the energy and half the spark time, it seems to make no sense to use 2 coils on a single igniter channel with an inductive setup or to use 2 coils on a single ignition with a CDI setup. Even with testimonials that say it "works fine".

Nearly 300 hp on a 3.0 street (10:1) engine on street gas. DC 62 102 lobe center. Single MSD.
Note the max power @ 6500. Factory RSR race engines barely made 315 @ 8000
http://forums.pelicanparts.com/uploa...1614116412.png
http://forums.pelicanparts.com/uploa...1614116412.jpg

3.2 Street engine, Mod S cams, SSI exhaust single MSD. We have since discovered that the M&K muffler in this configuration probably cost us 15hp.

http://forums.pelicanparts.com/uploa...1614116685.jpg
http://forums.pelicanparts.com/uploa...1614116685.jpg

Imagine how much it would make with 2 MSD! :D

And here I thought you had more style than the other squirrels....:D

I should do back to back dyno pulls, I have a 3.0 twin plug with a single MSD, now I'm going to install EFI with crankfire and 6 GM wasted spark coils.

I'm not getting rid of my old kit though, my webers dizzy and MSD will be going onto my new 2.7 project that I'm slowly collecting parts for.

Back to back pulls without tuning for each application will be almost meaningless but it's something.
If I understand the answers to my questions, the previous claims of back to back was simply disconnecting one CD box rendering the engine single plug.....hence the claim of 15hp reduction.
It was valuable information but not as informative as it might have been.

I know it's meaningless...that is except to me. ;)

I just want to have fun, my under sized webers, my crappy repop Jag cap dizzy and single MSD is fun.
I'm only doing the EFI swap because a) I got the system cheap for an excellent price and b) because I need a second intake and ignition system for another engine project.

I wonder If I can run my new ECU ignition only? So I can see if I at least feel a difference between my PMS TP dizzy with single MSD/two coils and the the crankfire ignition system.

I hope this is self deprecating humor. Run what you have and be happy to have it.
Cool upgrades are cool no matter how the "internet experts" criticize them.

IMHO, Product /design criticisms should be used to evaluate future purchases not to slam what others own.

Well, I just read through this whole thread and thought I'd weigh in and offer a physics based answer on the original 'Single box for twin plug' question. I've been an electronic engineer for 30+ years and also designed our CDI+ unit.

Will it work? Short answer, depends if the CDI unit used generates enough energy for both plugs.

In the case of using the MSD boxes, you are 'getting away with it' for a couple of reasons:

1) these units do store a lot of energy. The charge voltage is around 530V, vs the Bosch unit at around 350V (RPM dependent). Voltage is the dominant number in the energy equation.

I have to make an assumption here but it is not that wild. Let's say the MSD box charge capacitor is the same value as the Bosch, which is 1.5uF. So we can calculate the energy stored in the capacitor:

Bosch: = 91 mJ
MSD: = 210 mJ

(Energy = 1/2 * C * V * V )

2) Running two coils in parallel, the current will be halved in each coil so the energy is halved (E = IxVxt). So, each coil is 'seeing' 105 mJ of energy. E.g still a little bit more than a single Bosch unit delivers to a single plug.

So, you would struggle to run two coils from a Bosch unit, but you get away with it with MSD.

Personally, I think the primary voltage used by MSD is absurdly high which is why they stipulate changing leads and using their coil. There is not that much to be gained by going much over 400V but there is lots of potential for cross-firing between leads, tons of RF noise and rotors burning out.

The old MSD 6420 has less voltage and millijoules (480v and 115mj) than the MSD 6425 (530v and 135mJ). This is from MSDs own data sheets.

So, with 2 coils, you are getting only 58mj per plug with the analog MSD units and 68mj per plug with the digital units....and half the spark duration too.

Scott

Interesting. From that data, working the maths backwards, the MSD charge capacitor in both cases is 1uF. So, the later box simply runs a higher voltage. So my maths was slightly out when I made my assumption in my previous post.

The Bosch box voltage drops off with RPM - can be as low as 275V at high RPM. So that would be only 56 mJ. So, still theoretically possible with either MSD box.

The maths proves that with one box you are getting half the energy (as you rightly said). The question is whether that is enough and based on a comparison with a Bosch unit it does appear to be.

It is true that not having enough energy will degrade performance, but at some point having more energy does not make any measurable difference to performance either. Have proven this on a dyno since MSD makes no more power than our CDI+ unit despite more voltage.

How do you conclude half the spark duration?

As this thread seems to be getting more helpful to those of interest and less of a drama show. I will give a little more helpful information for the Pelican readers.
When you split your energy between two coils, one helpful way to keep your spark stronger is by reducing the resistance of the spark plug. Silver is your best conductor therefore if you have low energy you should choose the plug with the least resistance and today you can get silver plugs again. Copper is a close second in plug choices for low resistance.

See here:

http://forums.pelicanparts.com/9158818-post1.html

Although we haven't found a need for silver or cooper plugs, that seems like a reasonable suggestion.
15+ years of using this technique taught us to use solid core wires contrary to the recommendations of MSD. That is where the analog 6ALN comes into play. The digital 6AL reacts poorly to the solid core wires.

Following the MSD wiring installation instructions to the "T" is also important to proper ignition function and longevity.

We know that beyond a certain point "extra" spark energy does not produce more horse power, JonnyH has eluded to possible detriment to excess energy. What are the possible negative effects of "too much" spark energy?

It says he DIDN’T test two coils spark duration.

“ What I didn't check for, but perhaps will do another time, is check how much shorter the spark duration is with two sparks plugs firing at once. ”

Oops....wrong post:

http://forums.pelicanparts.com/9159766-post3.html

"I did a quick measure of the spark duration with two coils compared to one. These numbers are variable depending on the coils used and the plug gap. However, the duration with two coils in parallel with both gaps firing is approximately 1/3 the spark duration for a single coil in my testing. So, that makes the spark duration extremely short for the single polarity MSD output firing two coils in parallel. Only 10 to 15uS or possibly a little longer with high efficiency coils and a narrow plug gap."

Ok, but that is just a function of the amount of energy stored in the coil. I’ll stick to physics, if you have a CDI unit with twice the energy of the Bosch units, it should ‘charge’ two parallel coils as well as two Bosch units and the resultant spark should be the same.

It is worth noting that the 8 Pin Bosch units (fitted to the race cars) have a regulated 300V supply. This means there is no drop in spark energy with RPM like on 3 and 6 Pin boxes. This suggests that Porsche considered 67mJ to be enough energy for their racing cars. But don’t underestimate the Bosch black coil in this. They have a unique spec, not found in any other coil on the market.

Porsche did not use twin plug setups that would drop spark energy at high RPM. Based on that, and using the same coil Porsche used in their twin plug setups, what was the spark energy sent to each plug?

Yes they did. Both 3 and 6 Pin boxes drop power as the RPM increases. So at 6000 RPM you would be down around 50 - 60mJ per coil.

The 8 Pin boxes are 67.5mJ constant due to regulated supply voltage of 300V.

So if a single CDI box can produce 135mJ, then it would be comparable with two 8 pin Bosch boxes in terms of energy.

Sorry, I can't be much clearer than that.

NASCAR uses a power supply that boosts 12v to 18v for their MSD.
Do you have any thoughts about what that does to energy delivery.

Porsche only put twin plug CDI setup on race cars....you said race cars used the 8-pin boxes.

Early ST, RSR etc used 3 Pin boxes. Not sure what year the 8 Pin box came in but was on 956, 962, 935 etc. 8 Pin also on early Turbo

I keep hearing about how all Porsche race cars with twin plug used two CDs because two CDs supplies a "better" spark. It may have provided a better spark with the single CDs of the time but the main reason for two CDs was ignition redundancy. The distributors had two separate mag pulse units or multiple points to produce a redundant ignition.
Very few reproduction twin plug distributors have a duel mag pulse, hence no system redundancy.

Oh Henry. Let's not modify history. The main reason for twin plug was so they could tune the compression and timing make more power. Plain and simple. Even Randy Leffingwell's book "Porsche 911: 50 Years" says that twin plugs were too they could make more power. If my Paul Frère books were not in storage I am sure I would find references to that as well.

You need two Bosch CDIs because the energy would not be enough to drive two coils. I thought I'd made that point.

Redundancy certainly isn't the 'main' reason. The twin plug was conceived for more power because you are 'lighting' the mixture from either side. Two flame fronts sees more energy released from the combustion in a shorter time, hence more power.

Twin plug engines need a lot less advance than single plug. If you 'lost' a CDI box in a race, the power drop off would be substantial unless you could advance the ignition from the cockpit. Would get you to the finish line though. I've done the single/double test on a 375HP motor, it lost 40HP when the second box was switched off.

In my opinion the two reasons for twin plug are #1) Increase volumetric efficiency of the engine, many people do not know why they benefit from twin plug... The reason is you ignite the fuel on both sides of the dome of the piston. always have to explain this on guys wanting twin plug on turbo as the pistons are pretty flat and not much gain at all other than redundancy. #2)In race cars if one failed the other could get it through the race hopefully, (2 ignitions of course) There are some side benefits like lower timing and reduced timing advance but this is due to not having to light the fuel as early since your lighting it on both sides of the dome also reducing detonation enabling more compression also.

OK, "main reason" was a misstatement but it's fun watching heads explode.
Porsche was interested in endurance races almost to the exclusion of everything else. Finishing was paramount.