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With a standard coil the energy to strike and sustain the spark has been previously stored within the coil itself, coil's magnetic field, INDUCTANCE, actually. A 6 cylinder engine at 6,000 RPM fires a spark plug every 33.33 milliseconds. That's a LOT of time for a 12 volt source to store enough energy, overcome the coil's inductive reactance and thereby build up enough magnetic field to provide the spark energy. But now take that same coil, same inductive reactance, and tell me how long it might take the Bosch's 300 volt supply, or even the MSD's 450 volts, to build up enough magnetic field to COUPLE energy ACROSS the ignition coil now acting as a transformer. So I would suggest that either, OEM or MSD, would operate more reliably with a TRANSFORMER rather than the standard ignition coil. The way I read the MSD information on their blaster coil that is exactly what they have designed. For <$40 that would be a damn good investment. B.) "..WHO CARES..." Well, YOU SHOULD... First, what's the harm..? Second, the theory holds water, with enough SWIRL the second spark initiates a second flame front. Carrying the theory a bit farther that should allow you to reduce the amount of spark advance...a GOOD thing. |
Not wishing to fan any flames here, but I was reading about the new Ferrari F12 and noted the use of a multi-spark system in their 13.5:1 engine. No mention whether its inductive or CDI, either.
You can read this for yourself at F12berlinetta I daresay that Ferrari engineers know a thing or two about engines,.......... |
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BTW.. I just realized I was using a MSD coil with my MSD 6al... so I cant blame my coil on its failure.. sorry guys, my memory is going to hell. There's a +1 for lorens Bosch.. :) When I said "who cares" I meant, we have bigger fish to fry keeping these old school sports cars on the street. By the way, due to its smaller size.. the "msd streetfire" was a thousand times easier to install than the 6al.. just sayin.. tool me maybe 20 minutes to install it physically.. vs hours on the 6al.. A pematune takes like 20 seconds however ;) as well as that bosch thingamabob ;) At this point we could be discussing spark plug gap and power gains/losses.. waste of time.. more gains to be made on a good tune up. If this were in a racing forum it would be appropriate. But, you'd still have a hard time defending the bosch over computer programmable ignitions like megasquirt etc... for the cost of the bosch you could be well into current technology where you could fire your plug many or few times with whatever duration you want at given rpm/load/speed/gear/ yadda yadda yadda.. :) This loren guy knows how to fuel the fire.. I will give him that.. sort of a trollish post ;) no disrespect intended.. as I've seen good information from him. I do miss the cool whine the bosch makes though.. :) |
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The inductive reactance of a coil would typically not allow the inductor to be "recharged" in a short enough time to provide a second spark in a timely enough fashion. However, the capacitor in a typical CDI design is partially recharged, ~70-80% actually, by the collapsing magnetic field of the ignition coil(transformer) once the spark extinguishes. Which is why MSD is able to provide those 8 sparks in quick succession. Also, the duration of the CDI "spark" can be quite easily "squelched". |
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Nice post; thanks. |
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Let's pick 6,000 rpm. 6,000 revolutions per minute divided by 60 seconds per minute 100 revolutions per second The 911 crank throws are offset 120 degrees, so 3 ignition events per revolution. Therefore 300 ignition events per second. 1/300 = 3.33 ms per ignition event. You are off by a factor of 10, one order of magnitude. Next: an inductive coil does not charge, or discharge, instantaneously, and the spark duration is nonzero in length. The dwell period, or time that the coil charges, is defined as the number of degrees of rotation between when the coil primary negative is grounded, and then let float (akin to points opening). This is around 38 degrees of rotation per event. For six events, 228 degrees of charging per distributor revolution, or a 63% duty cycle. 3.33ms * 63% is 2.079ms, that is just the charge time. In fact, the coil energy is even less than the cutback caused by the dwell period-- the coil, if given a long time to charge, would approach full energy after around five time constants-- but if you do the math, you barely make it past the first time constant, or approximately 63% of the theoretical charge, before you run out of time. So not only does the coil get cut back by dwell, it gets cut back by the fact that you are barely past one time constant, and the coil energy hasn't peaked, by the time the ignition event occurs. Everyone knows this, and this in fact is the reason that Porsche went to CDI in the first place-- with the current limit of about four amps through points, and the energy requirement to light the mixture, there was not sufficient time for the coil to charge and discharge fully between ignition events, resulting in reduced ignition energy at high RPM. CDI, with its short capacitor charge time that was largely independent of dwell, was the answer to the RPM and energy problem, at the sacrifice of spark duration. We discuss this in detail here, with more of a focus on math than who's right and who's wrong. http://forums.pelicanparts.com/porsche-911-technical-forum/640218-crane-xr700-capacitive-discharge.html |
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How do you propose that a CDI circuit VARY its spark intensity and duration? To get variable discharge time you need variable resistance in the discharge circuit, fine. How are you going to vary the intensity, with different capacitors? Explain. |
"Carrying the theory a bit farther that should allow you to reduce the amount of spark advance"
Just think: With triple plugs per cylinder and multiple sparks no spark advance would necessary. Interesting that this wasn't thought of before. We'll have to email to Porsche & Bosch engineers the link to this thread. Isn't amazing the knowledge that gets developed on this website. Most can't troubleshoot simple engine problems, but new theories in automotive engineering are abundant here. I'll bet Porsche has assigned a full time engineer to monitor the great theories that get posted here, right? And they won't even have to pay, since the new theories are now in the public domain. "You are off by a factor of 10, one order of magnitude." And a lot of other erroneous information! "Now Steve, "fan" the flame? You know that Ferrari used nothing more than gimmicks to make those 720 horses right?" Does either of you want to explain in technical detail how the link relates to specific data measurements & analysis presented in this thread other than that Ferrari has three multiple sparks stated a in single sentence? Is this all you could find and have? What a complete joke! Unknown from the Ferrari promo is: 1. The duration between sparks, i.e. MSD multiple sparks occur too late - 1.6ms after the 1st. 2. The burn time of the sparks, i.e. MSD uses very short burn times - about 1/2 of the Bosch. 3. Whether CDI or IDI, i.e. CDI has very short burn times. 4. Whether the multiple sparks occur over full RPM range, i.e. MSD multiples end @ 3K RPMs, hardly of much value for performance. 5. The design of the combustion chamber. Try again and this time get & provide some technical details other than doing a mindless search on multiple sparks and posting the first result that has one sentence about it. A total waste of time to sit thru a lengthy Ferrari promo and find one useless sentence. Bottom line: Still waiting for some dyno data and or some emissions data to support the MSD marketing gimmick. A little more difficult to focus on the issues and data in the thread than to link to hyperbole, right? And when that can't be achieved, just do more of normal personal attacks, e.g. troll, as usual. |
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Loren, you're doing nothing here but degrading your own reputation as a CDI repair GURU. Stop. |
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His intent starting this thread was to drum up business and all he did was chase it away..... Scott |
11 pages and what a mess...
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someone put this thread out of its misery...
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I'm amazed that Porsche or Ferrari hasn't jumped on the opportunity to have some of them run their motorsports programs. LOL Quote:
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[QUOTE=Lorenfb;6764903]""
"Now Steve, "fan" the flame? You know that Ferrari used nothing more than gimmicks to make those 720 horses right?" Does either of you want to explain in technical detail how the link relates to specific data measurements & analysis presented in this thread other than that Ferrari has three multiple sparks stated a in single sentence? Is this all you could find and have? What a complete joke! MSD explains multiple spark as an advantage to cleaner mixture burn at idle and just off idle. It says nothing about a performance gain at 6,000 rpm which you consistently refer to. I do not have the means to test this theory but must admit that the Ferrari add seems to point at the same reason for using multiple sparks. They mention it in the same sentence as lower emission so my take is that it has to do with idle and off idle fuel burn. Since you are the one claiming multiple sparks have no benefit, why is it that you cannot provide the same data you ask for? You say it doesn't work; prove it. The FACT that you cannot is the real joke. |
I take it back.. this thread is no longer a waste of time.. its now some really good entertainment :)
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"MSD explains multiple spark as an advantage to cleaner mixture burn at idle and just off idle."
If MSD makes the claim, it's their responsibility to provide the data to support the claim! As mentioned before, there are many gimmick automotive products where claims are made and no supportive data are provided. Where are the data? |
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For those of us who understand the theory, seemingly SOLID theory, behind the MSD, and now Ferrari, multi-spark design there is no documentation or supporting data required. On the other hand you are claiming that there is NO benefit, so it behooves you to prove the LACK of same. Feel that wind chill...??? |
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