MarkRobinson

Thanks Joshua. BTW have you any knowledge on the 32v (dual coil, dual ignitor) ignition system with the MSD coils? I have a race car on-boost and wouldn't mind a better ignition setup. Also, I make plug wires for Pelican (solid-core Beru setups, so if you wanted to host a product that Pelican didn't carry (ie, any 944, 928, 965) we should talk.

Cheers, Mark.

FeralComprehension

Given the well-known poor quality of the silver Brazilian Bosch coils it's possible that this community would be willing to fund some development time if you promised to provide a technically rigorous answer. It would be awfully nice to have a readily available and easily implemented alternative.

Rogue_Ant

Mark,
I believe the 928 uses two of the same ignition modules as the 964/968/944S2. The Bosch part number is 0 227 100 124. Can you confirm that this is the case?

I will keep the 964 crowd in-mind.

Rogue_Ant

Loren, you are quite right that I don't adhere to your faulty assumptions.

I truly don't understand how you believe your assumptions and oversimplification trumps actual test data and measurement... I also don't expect you to actual read this post and consider the information. Every single interaction I have had with you has shown me that you make a conclusion well before any points have been made. (For the others reading this thread, I am compelled to try to put this to bed...)

When I use your BS assumptions and show the erroneous results, then you move the goal-posts - yet another common fallacy.

Here is the stock 964 ignition dwell time table (time in mS):



Notice that the table has two axis, one for system voltage, and the other for RPM. The DME does not charge the coil for a static time, rather the charge time is dependent on RPM and voltage. Therefore, if we pin voltage at 12v (like your assumption), we can easily see that charge time varies from roughly 53mS to 2.2mS depending on engine RPM.
(If you do not understand why the table data is as-such, then read here as I do not want to rewrite all of that)

So, if we again try to use your current calculation for something outside of the bounds you need in order to make your calculation work, and this time I'll use the inductance value that you posted:

I = 52.7mS * 12v / 3.6mH
I = 175.67 amps

...really? Your assumption results in 175 amps. And you are OK with this? at 12 volts, that means 2100 watts - that is 110v MIG welder level of power.

Ok, even if we say the 40RPM row is pretty much never used and throw it out, lets use the 240RPM row, since that is very near engine cranking speed when starting.

I = 11.7 * 12v / 3.6mH
I = 39 amps

Wow, that is still a huge amount of current... Obviously the coil would saturate well before this, but lets just carry your calculations through:

Energy = 1/2 * 3.6mH * 39^2
Energy = 2737.8mJ

An energy level of nearly 100x what you state is necessary. And you are OK with this?


Your oversimplification of the circuit only works with very limited bounds. And even within those bounds, you are neglecting quite a few things. Best-case is that your calculations give a result within 1 magnitude of actual result. However, for the majority of coil dwell times, the majority of engine operation, your calculation is useless.


Regarding spark energy, you are failing to understand how the actual ignition-combustion process happens. The air/fuel mixture is not static in the cylinder; it is not sitting there motionless. Rather, the air/fuel mixture is tumbling and swirling around, and is not an ideal homogeneous mixture.
If, and only if the air/fuel mixture was static, an ideal homogeneous mixture, one set temperature, and the piston was not moving, then would you be correct that once the mixture is ignited, any remaining spark energy is wasted. But engine reality is far from a simple ideal.

The air/fuel mixture is moving, and as such it possible that when the spark plug ionizes, that the surrounding mixture is poorly homogenized and doesn't ignite. If the spark plug can stay ionized for a short time, then the tumbling & swirling of the air fuel mixture will move a different part near the spark plug and possibly ignite. If the spark plug did not have this "excess" energy to keep the gap ionized, then there would have not been a combustion event, resulting in a misfire.
Since combustion is not instant, we know there is a flame-front, or propagation of the combustion throughout the cylinder. With a longer spark duration, there is also the possibility of igniting multiple parts of the air fuel mixture, as the tumble/swirl can outpace the flame front. Porsche obviously saw the benefit of multiple ignition points - since it used two spark plugs per cylinder, ergo two ignition points.

An analogy (though still overly simple) would be the difference between lighting a bon-fire at one point along the perimeter, vs lighting it at multiple points. The one lit at multiple points is going to achieve complete combustion much quicker than the single point ignition.


Penultimately, the 964 DME only provides the logic signal to the ignition module. The ignition module does not care if the logic signal comes from the 964 DME, the 928, the 968, etc. In-fact, plenty of aftermarket ECUs have made use of this ignition module, MegaSquirt for example: http://megasquirt.free.fr/sources/MS/manual/ms2/Bosch_124.htm

If the dwell time is known, then the equipment providing the dwell time logic is irrelevant. Regardless, for the data on my webpage, it was using an entire 944 ignition circuit: DME, wires, coil, etc.


Finally, you keep trying to force this straw man argument about inherent power gains. At no point on my webpage, or here did I say that there must be an power increase. No, if you actually bothered to read my webpage instead of predetermining what it said, you would have found that the only thing I talk about was the differences in coil energy - especially as RPMs increase.

Goughary

I'm all good with the two of you disagreeing with each other, and am enjoying reading the banter...and interested in both points of view..

That said, these "argument" threads break down quickly into something not fun nor interesting to read. So in view of the fact that we are in a public forum, could you both keep arguing and keep proving the other wrong, but try to keep the name calling and mud slinging down to a minimum? Otherwise call each other on the phone and have it out.

I appreciate both if you and your respective knowledge. Keep it up.

Rogue_Ant

Goughary,
There is quite the difference between disagreeing with someone, and blatantly attacking that person.
You can be a skeptic and still be respectful - the two are not mutually exclusive.

I did not just jump out of the woods at the sight of Loren. He has unilaterally came into my threads previously, with his same rhetoric and attacks - always failing to rebut any of my points. His only intent was to do harm to me or my business.

The simple fact is that he probably sees me as a competitor to his own business, and decides the best approach is to attack me, as he has done to so many in the past...

Goughary

I realize that. And have seen it before, with other people as well. I'm just asking that before it gets nasty, the argument continue and name calling and ugliness are curtailed before it gets horrible to read as a bystander. That's all. I'm not taking sides...

Anyway, my apologies that my post was directly after yours. It could have easily come after one of lorens...it just occurred to me to stick my nose in tonight....lol. I usually don't. But if like to see the smarter guys here stick around. And if we can't be civil while in disagreement, then these discussions/arguments won't happen since nobody will be there to read them.

So no argument out of me. I'm not taking sides and you guys haven't gotten too out of control yet...but I've seen this stuff get way out of control...so I piped up only to be a voice of reason before round 3...

Rogue_Ant

Fair enough, and I agree - usually I try to keep any disagreement reasonable.

Loren has lost any margin left of my patience for him, so I probably come off as harsh to the bystanders. For those I invite to take a look at the history of both my posts and Loren's - and then come to a conclusion.

Lorenfb

[QUOTE=Bob Rouleau]Hi Lorenfb,

"The post that you created in the following thread has been deleted"

Thanks Bob! Speaks well for an open forum.
Maybe you should delete all my posts in the thread.
That way you can fully 'protect' your advertiser against
his ignorance. That's what it's all about, right?

Bob Rouleau

Loren, you know the rules about promoting your business. Furthermore you know the rules about insults too I bet.

Regards,

Navaros911

So euhm... was there a conclusion to this?

Real world tests and experience would be nice to see.

I suspect one of my coils may be going bad. Have some top end hesitation and low end rough running on humid days only. Could be wires too, but it is so short of an issue on the top end that it feels like something else failing.

Already broke the 2nd dist belt checking this out... so don't want to break anything else along the way.

She's going to the mech for this since I have no time with a 2 month old and I wanted a second set of eyes to do a good look over - something I have done once a year at least.

Goughary

Also try putting a multimeter on each wire and check resistance. Should be 3 ohm on each cable. There are 4.5 turns to screw in the wire to the connector. After years of pulling plugs off and doing service, a few of mine had backed out and were no longer connected inside the boot. And the electrics were for a time jumping the gap and still functioned, but as they got worse, I had more and more issues...

Navaros911

Thanks Goughary... that's a good point you're making.

Alex Sol

conclusion for me? i like the msd blaster coils... i have bosch ones still in spec and they seem to work also. silver and black. also running the blacks on my 951 but will try the msd for sure...

that said, my 964 runs very poorly right now... working it out and it seems to point to the afm...

SMTCapeCod

Just checked, confirmed that is the case.

Anectdotally- I installed a Digital 6 and HVCII coil in place of the factory ignition on my '83 928 Euro. My perception was much quicker cold starts, modestly smoother idle, increased throttle responsiveness. Wish I'd calculated fuel efficiency/checked the exhaust chemistry....That was after a prior attempt with a perma-tune ignition/coil and with separate Nology coils, all of which proved suboptimal at least the way I had them installed/configured.

Long ago, I had an 85 US 928 that came with two Jacobs ignition units already installed. That car was crazy strong...I assume that it may have had the cams advanced, but it was otherwise stock.

Installed a Jacobs Ultra Coil on my 924S long ago, no discernable difference pro or con.

I'm interested in improved coil(s) for my current 86.5. One issue that I'm not clear on, is that factory and OE ignition wires are purported to have resistors. Actually I suspect that the terminal ends just provide a specified amount of resistance, but none-the-less wires without resistors are far cheaper. Maybe Mark is clearer on this? I'm not talking about noise suppression winding, fwiw.
The factory wires are a big hit($) on 928 32V, I'd hate to cook them with a more energetic coil...but would like the reassurance of stronger mj output.