While not Porsche specific, I can offer what I've seen first hand on the dyno with respect to ignition systems. (I was a nascar crew chief for over two decades and fortunately didn't pay for dyno time, other than race fuel).

If it's lightin' the fire, it ain't gonna make more power with a stronger ignition system. There is no more magic as long as the mixture is fired. But if you open up the plug gap, it will make more power, until you open the gap up just a wee bit too far and the engine won't start. Power increase was about 10 hp with increased gap (about 1-1.5%). And if your ignition system is strong enough, 0.100" gap worked really good, other than tending to crossfire in the distributor and blowing holes in the rotor. Be careful that the piston dome doesn't close up the gap on your plug though.

It was common knowledge that we used 2 complete and separate ignition systems but only one distributor and one plug per cylinder. MSD boxes would quit working more than we were comfortable with, so the other system was a backup to the first, with an "A-B" switch controlled by the driver.

With respect to twin plugs and disabling one side, it doesn't surprise me that it lost power, not because two are better than one, but that the ignition timing wasn't then optimized for single plug. Much like doing a "mag check" on piston engine aircraft. For a more correct test, test optimal spark timing under each scenario. I doubt that the power output would vary as much if tested that way.
FWIW, YMMV

Okay, you make contradictory statements in that paragraph. If it is just about "lightin' the fire", plug gaps wouldn't matter any more than energy at the plug. So, it's either just about "lightin' the fire" or it also matters how you "lightin' the fire".

I thought it was explained pretty well, but I'll explain it a little better. Without changing the spark plug gap, it will not make any more power. Any power increase comes from increasing the spark plug gap. But it will LOSE power if the ignition system is weak enough that the engine is misfiring.

Dannobee.. I agree with you. I am going to try to put it more direct for the person that asked the question as I was not direct enough in my answer.
An ignition system has the energy to complete a spark up to a certain distance. A bigger spark makes more power.. If you double the demand on an ignition system you reduce its energy to complete the spark by 50%. So both answers are correct.. An ignition can work with two plugs if the gap is not too large in most cases. If you add a second ignition source doubling the energy and you do not change anything else the result is probably very minimal or maybe nothing. I indirectly was trying to state that and did a poor job. This is my last attempt at this subject and I did it for clarity to the person who asked the question.. Depending how you look at it Henry was right and Winders was right. I am right in stating it should not have spun this far out of control to help a lesser experienced person gain resolution to their question. Lets not talk about duty cycle in the ignition system because that would throw more confusion to newer people.

Yes, of course, you have to tune to take advantage of twin plugs. You have to tune to take advantage of available energy in the ignition system. You have to tune to take advantage of the fuel you are using. Nothing happens magically in a engine. Any changes made have to be tuned for....including better and more air flow into the engine and exhaust out. What can be tuned? Cams, cam timing, ignition timing, spark plug gaps, spark plug types, fuel type and octane, intake type and size, header type and size, etc.

You can't take an engine, twin plug it, and make no other changes and expect it to be much, if any, better. You have to tune the engine to take advantage of twin plugging. The same is true for the ignition system. If you run one ignition box with two coils you have to tune for that. If you run two ignition boxes with two coils you have to tune for that. You would probably make small gains with out running plugs gapped to take advantage of the increased ignition energy, but not what you would gain by using plugs with the appropriate gap for the increased energy. Putting 106 octane race gas in car tuned to run 91 octane buys you nothing but some pre-ignition protection. You have to tune the engine to take full advantage of higher octane fuels. If you put an air filter on the engine that flows more air, you may gain power, lose power, or have no change. You need to tune for that too.....

The engine is a system. The system has to be optimized (tuned) for any changes made. This concept was a given for me.

I love these technical discussions where some of the real knowledgeable engine builders give us the benefit of their years of experience.

I have a non technical solution that I would offer:

If I build a twin plug engine and spend that kind of money, I am going to use dual ignition boxes because there is no downside other than cost of a second MSD box. Just checked and Summit sells the MSD box for $285. I may be missing something that would raise cost somewhat, but at this level of investment in an engine build, it is probably cheap by comparison.

You didn't miss anything. You are correct.

Well he may have missed something. I love these "it's only a few bucks more" arguments.

Please understand that this exercise if offered with humor not malicious intent


First, why buy the cheap MSD boxes. The higher performance boxes are only a few dollars more? The cheaper digital boxes seem to have a pretty high failure rate. For that matter, why not buy the Bosch CDs as used with early twin plug racing Porsches.....Of course those were special 8 pin CDs but hey.....why not. Lonny @ Permatune makes a great replica.

Then there's the installation ...Where are you going to install the second unit?
We like it out of the engine compartment away from RF signals and heat. Usually under the drivers seat.
I assume because your $285 is an "all in" the extra CD will install itself.

Now, in this "it's only a few bucks more" build is the engine going to sustain high RPMs?. Are we using stock rods....if so, ARP bolts are just a few bucks more.....oh wait...we're doing this "right" so why not Carillos...or even better Pankl titanium?

The only way to make "real HP" in a small engine is to spin it...right?
Careful, for that you really need a special crank...I have my own made to my specs but because you have a few more bucks, why not design your own?

Is this engine going to be built on a tired old case? Surely a new case is better and only "a few bucks more". I know because I have some....want to order one now? They won't last long.

As you can see "it's only a few bucks more" along with "while you're in there" are terms that need serious consideration every step of the way.
Cheers SmileWavy

I really appreciate all the input here, I love the way Porsche people are happy to have string and healthy debate to take our mutual interest forward. It does become an academic only discussion at times, but from my POV this great, feeding our requiring minds, as long as no one takes it too personally. Here’s a few observations ..
- It seems twin plug with reduced spark energy preferable to single plug with a lot.
- Modern CDI ignitions probably deliver more spark than is required for a standard engine.
- Therefore it may well be beneficial to really open up the plug gap in a single plug installation. Anyone actually tried .100 or anything near it in an old 911?
- Modern CDI boxes probably produce way more spark energy (150MJ) than Bosch CD boxes from 50 years ago, sufficient to ‘light the fire’ in a 10:1 street car.
- The solution needs to be appropriate for the application .. high CR, full race, best of everything. Lower CR street car, solution appropriate for state of tune.
- A single CD box firing twin plugs in a street car boils down to a reliability issue, as it works the box much harder.

Interesting read while stuck at Denver airport for 1 hour layover.
In the water cooled world you can never have enough water pump. In any engine you can never have enough ignition energy. Whether you use it or not.

In these hemi engines, there are absolute benefits to using CDI ignition. If you are looking for a less expensive setup or have some emission requirements to met then inductive is a good choice. But you should expect less energy at the plug tip.

I have not read here anything about how the fuel mixture is ignited under compression. The plug starts the cycle but it’s the heat that is generated in the chamber that ignited the fuel mass. The more energy dissipated the greater the explosion.

The leaner the mixture the more energy you need as well.

The Ignition function is always taken for granted, buts it’s the most important function and the last in the making of rotational torque.

Splitting the energy stored in the CDI must have an effect on the energy at the plug. If it has not been seen, I think other factors were involved.

CDI coils act as transformers which is why they need very lower inductance levels. Most modern CDI units produce anywhere from 100 - 500 mJ. Inductive ignition rely upon the windings within the coil to generate their energy. The Igniter is just a digital switch. The coils produces the energy at the plug tip. Most modern inductive coils produce anywhere from 35 to 100mJ. Typical they are around 45 - 55 as most modern car engines do not require high energy coils with small cylinder head chambers, and low RPM limits.

Neil, your correct, I tried to keep it basic for the average non tuner/engineer questions.. But the post got a little crazy I think. I am waiting for someone to point out you said explosion rather than Burn. I am not I was just shocked some time went by and no one jumped on it.. LOL
I thought about saying is we are going to split the capacitive discharge unit why run two coils, we should split the coil wire and feed both caps.. BUT I do not see that kind of stuff as good humor and it isn't productive and the goal needs to be help the people and not make drama. Most of the people on here, like Alton, Henry,Winders and you have their strengths and weaknesses compared to each other and all are pretty smart with good intensions. I encourage in the future we all put our best foot forward to help support each other and keep humor out of it.

I enjoy the technical discussion as much as the humor ! I have a lot more experience building Ducati engines where the air cooled variants also respond very well to a second plug.

Twin plugging my 3.2 is in my future plans and this thread has offered great advice.

Regarding the quality of the MSD (what I currently have on my 3.2) what are some superior choices others have used? M&W ?

Each of us have different opinions, I found crane digital boxes to be excellent years but they got worse. I have had 1 MSD go bad over about 200 in the past 30 years. The biggest issue with the MSD if often a coil issue in the magnetic distributors, quite often MSD's are wired in reverse polarity on the magnetic output from the factory distributer, they will run but it causes premature failure. The green feed wire from the star wheel often has the polarity reversed. The internal insulated wire should be the positive but often the outer braided wire is the positive. This has been the issue quite often, rather than fixing the distributer I have reversed the wires to get them correct on polarity more often than not. The MSD is far from the best but I can say it is rare for me to have a problem. It is possible others have have had terrible luck with them and does not like them. In my experience the least reliable ignition is the prematune. Many times I have gotten calls "my car is dead on the side of the road" and I replace the permatune a Bosch 6 pin and away they go. The Bosch is a good unit, on cars running carbs where the air fuel ratio is not spot on controlled by a fast ecu like a Motec 130 I prefer the MSD as I think is had more energy than the bosh and I can run a wider plug gap to help with a wide range of air fuel ratios and gain a liter power.

Just go to a race track and look at the air-cooled race cars. If they are not running the stock ignitions or CoP setups, odds are they are running some version of MSD. They just work and are not ridiculously expensive. My experience at the track has been coils are what go bad. It's best to get the sealed MSD coils as they seem to last longer. I have never had anyone come to me looking for a spare MSD ignition box...but have had people come looking for a spare coil on many occasions. I don't think I have ever seen a failed MSD ignition at the track....though I am sure they do fail sometimes.

Best coil for MSD is black Blaster 2 high vibration in case someone is looking. The 6Al digital works well thankfully they make them black now, I never liked the red.

Yes, the black coil is the sealed unit that can be mounted in any orientation. I think some people the red ones something other than vertical and that causes them to fail earlier than they should.

FWIW....I have been running a single MSD driving two Blaster coils in my twin plug RSR spec motor for the past 15 years on and off the track. Runs great.

Sure it does....it's tuned to run that way.

I also have a 3.0 twin plug, RSR style pistons, weber 40's, web120/104 cams PMS/Jarvis dizzy (MSD trigger), etc all running on a single older 6AL with two MSD high vibration coils. It's very powerful, I have a poop eating grin every time I drive it. I might do some DE or an AX but it's a street car, but it's my summer DD say at least 60miles every couple of days, so far it's very dependable.
Only real bad is the carbs are a bit thirsty and girls don't like the smell a carb performance car emits.

http://www.914world.com/bbs2/uploads...4034_thumb.jpg

Looks like nice motors, The MSD high vibration coil by memory is Gel and regular ones are liquid. The liquid ones do not live very well upside down. The High vibration ones like in photo above seem to not care how they are positioned. Speaking of the fumes from fuel, I think that can be adjusted out.

You can guys can provide 20 examples of single MSD ignitions with 2 coils if you want. That doesn't change anything said previously in this thread.

Mark, I rcommend putting put a set of RSR spark plug wire retainers on those bottom plugs....

In a CDI Ignition system, the energy is created and stored in the CDI unit. The coils add not energy to speak of. So adding two coils will make no difference. But, you should expect the energy released at the plug tip to be less is the output of the CDI is shared at the same time. How much I do not know as I do not use MSD nor have I ever shared one CDI unit with two coils.

An engine is the sum of its parts and the Ignition system is one of these parts. In my opinion, it is one if not the most important part. You can have all the fancy parts included within your engine but if the Ignition is weak, your parts are not been used at their full potential. Ignition is the last function to happen before the mixture is ignited.

In any engine, performance expectations and the engine budget have to be in sync. If the budget does not allow for a high end Ignition system, then compromise has to be had. However, in my opinion, other costs should be considered first before compromising on the ignition system. This been said, I do understand that the cost of the lower end ignition systems have their place. You have to understand that failures can and do happen with any part and more often happen with parts made to a lessor quality.

To say that these lower quality system have been working for years and the car runs great, is somewhat short sighted is the other systems available have not been tried. Anything will feel great, but maybe another system would feel even better. An engine with contact points inside the distributor and a single coil, will run the engine. To some, just fine.

I have been using and selling for over 20 years a system made in Australia. Its made to a very high quality, a level we require in our engine builds.

But I will also give any CDI system its due credit over any Inductive system used on these early hemi-headed engines. The problem with 12 plugged engines is the complexity of any CDI system if a Distributor is not used. It requires 2 6 channel CDI units and 12 coils. Lots of wiring and lots of HT wires. In many cases an ECU is required.

Inductive Ignitions came about due to the long duration spark required for emissions. Cost also was a huge driver here. To fit multiple Igniters is vey in expensive in comparisons, and 12 COP units is the same. The wiring is a lot simpler too. Unfortunately the energy released is low and the engines performance will suffer in comparison. Add to this, you have limits on engine RPM and have to program coil recharge times to make sure the coils are fully charged. More coils does help here, but the energy is still a lot less.

The higher the energy released, the less engines are prone to knock as well. The higher in cylinder temperatures created by the higher energy levels, allows for a faster burn time and the end gases are ignited before they ignite themselves from pressure.

In more modern cylinder head chambers where the volumes are a lot less, Inductive Ignitions can be used with long durations but the ignition maps look completely different. All are typically water cooled as well.

Choose wisely and in many cases if the low end MSD or Inductive systems work just fine for your use, enjoy the engine. Its not always about how much money you spend.

Thinking about it, these testimonials about single MSD on two coils, one could conclude their pretty good boxes to serve double duty. I doubt a Bosch or premature will not hold up to that. Good to share on the forum.

But they aren't serving double duty. They send out the same amount of power the same amount of times. The coils are splitting the power.

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Winders.. You are correct.. Have to stop multitasking as much.

Only because you did not like what you were being told......

You mean this?

There you go confusing one thing with another again. But you go right ahead and keep missing the point.

As a general rule, the A wire is the shielded wire in the Porsche green wire (930 602 907 01) connector and if reversed the distributor will fire out of phase.
The problem with "general rules" is you have to know the exceptions.

I watched a very successful race team explode an engine because they were unaware that you reverse the wires you can destroy an engine. They knew the rule "coated internal wire is A" but they didn't know that their clockwise distributor was the exception.
What they didn't realize like most people, is that clockwise rotating Bosch distributors have reverse polarity. The clockwise distributors (euro 3.0 Carreras and 3.0 turbos)have the wires reversed. The factory identified the reversed polarity by making the connector blue as apposed to green. The blue wire was discontinued years ago so the only reasonable solution is to run the green wire and reverse the wires at the box.
You can (and we have) re-positioned the star wheel but that is an unnecessary exercise.

installing an MSD help tip's. #1 large red wire can attach at the large positive terminal on the starter do not use the existing feed wire for the previous as main power supply. #2 if you are not installing a new distributer and you know your ignition timing is correct your timing will be the same with the MSD. #3 check timing after installation of new MSD before you drive car if the timing on the ignition is the same as before your polarity on the magnetic signal is correct, if all of the sudden the timing reads about 60 degrees off "typically advanced"you have to reverse the magnetic signal from the distributer. The MSD will run with the polarity reversed but usually the ignition will shut down and stop working after some time driving the car in a mysterious fashion and restart after it cools often. #4 if installing a new Distributer rotate the motor to TDC #1 and point the rotor in the distributer at #1 spark plug in the distributer cap. Start the motor if the timing reads around + or - 10 degrees from TDC your magnetic signal polarity is correct, if the timing light says it is off by a large margin you have reversed polarity on the magnetic signal from the distributer. Many MSD units that get a bad reputation are often because of a reversed polarity on the magnetic signal. I added this to help do it yourself individuals make their install much easier.

When we send out one of the twin plug distributors we build, we include a these simple instructions. They are applicable regardless of the ignition you choose.

http://forums.pelicanparts.com/uploa...1611672786.jpg


http://forums.pelicanparts.com/uploa...1611672841.jpg

http://forums.pelicanparts.com/uploa...1611672859.jpg

Hum, again this is where we do not to clash technical minds because this is not a help to the pelican people. But I do not think the rotation of the firing order determines the polarity output from the distributer. The internal shielded wire in the green wire should always be the positive in the magnetic output. The a/c wave generated is the same either way you spin the distributer. It has been years since I built distributers but my reason for posting this is I do not want people to assume that if they have a counter clockwise distributer it means the polarity is reversed. I have used hundreds of counter clockwise factory distributers and sometimes there right and sometimes there not. This is not referring to Henrys distributers I am sure his products are good but I don't know much about them. This is about stock distributers and is to help Pelican people install their system and have it work properly.
To summarize what I am trying to say as the post I made above. Please use the simple few rules I posted above to check your polarity when installing a new ignition unit. I like Henry and I am not trying to have a competition on this or a heated debate, Both Henry and Myself will get it correct 100% of the time. My reason to push people to check it is you will also get it correct 100% of the time rather than looking at a diagram and assuming your equipment matches the diagram.

Back in the day Porsche made 2 wires for the Mag Pulse 911 distributor. The Clockwise rotating distributors like on the 3.0 Turbo had a Blue wire, while the CCW dizzy's had a Green. It was not only a difference in color...The wires were moved internally to correct polarity.

The effects of rotation on the Mag-Pulse is verifiable on a distributor machine.

My distributors are based on production Bosch distributor is all cases. The reversed phasing/polarity is a fact.
On all Porsche pointless distributors delivered as standard equipment, clockwise distributors have a reverse polarity A vs B connector to the counterclockwise distributor. The AC wave may be the same but the relationship to the star wheel and the coil changes.
The fact that Porsche made a different connector wire (blue vs green) for early pointless distributors (clockwise rotating) is a pretty good indication that something is difference. Both plastic ends are the same. They both run a shielded wire.
So, electrical experts, please explain what might be different to us uninformed?

If memory serves me, Andial actually made an aftermarket connector wire when Bosch discontinued the blue wire.

If you really want to have some fun, check the polarity/phasing on a mid 80s BMW distributor. They have the same internals as the pointless 911 Porsche distributor. They rotate CW and are wired reverse to the CCW Bosch distributors in 78-89 930 and 78-83 911 SC.

Good morning dude.

You guys should listen to Aaron. He knows more about these distributors than anyone I know.

Happy Tuesday Henry!

Here's a side note about humor.
My post about "just a few bucks more" is an important commentary on the snowball effect. It was not intended as a referendum on the virtues of any one system over another.
If we can't add a little humor to some of this tech shyt, life gets pretty boring.

Although you may be having gook luck with the digital 6AL our experience is different.
The analog 6 AL prior to the most recent digital boxes were far more reliable.
That is why we spend a little bit more and are now recommending the analog
6 ALN.

I am fine with the MSD 6AL that Henry likes, I did not know they made it any longer, Advantage of the digital for me was the ability to dial the rev limiter to whatever I want vs the plug in rev limiters on the 6Al. Both "soft Touch" rev limiters feels like someone hitting the back of your helmet with a baseball bat. When I used aftermarket ignition systems the best one I ever used was the Crane digital box that was blue 20 years ago but they were about $450 each back then. One thing I used MSD made that I do not think they make any longer was there timing computer. It ended grinding down weights and finding lighter springs and all of the madness compared to pulling the weights out of your distributer and mechanically advancing it to wherever you wanted your total timing. It also enabled you to pull degrees in the higher RPM that you could not do with a regular distributer. MSD now makes like a 6ALBT or something like that that is excellent for CIS turbo motors because you can pull timing from boost at what ever level you want and you do not need to rely on vacuum canisters on the distributer. I hope everyones efforts on this thread help out some people.

When I made my 3.2 distributor functional to work with my 46mm PMOs I used BMW, Mercedes and Porsche Bosch parts. It is surprising how similar all the Bosch distributors are from the 70s-80s. Hell, it has BMW 2002 advance weights in it.

I wired the analog MSD 6AL the "correct" way and the car would barely run and clearly was not happy. When I checked the rotor phase it was Way off and I thought I had made a mistake but reversing the polarity brought everything in line just like Henry is describing.




Winders, would you be OK if someone used a MSD ignition differently than you did on your engine?



I don't like the Red MSD case either but a can of PJ1 satin black case paint fixed that right up.







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