Twin Plug Cop Ignition Dwell setting

[Porsche930Targa]

I am running a MS3 Pro on a Porsche 911 turbo.
Motor is twin plugged with Toyota Denso Coil on Plugs.
I have read that optimum dwell setting for these coils range from 2 ms to 2.5ms.

Because I am running 2 plugs (coils) per cylinder, is there any benefit in reducing the dwell setting to 1.5 ms.

If the car sits idling for extended periods, I get a slight misfire.
Just wondered if this was due to heat.

Thanks in advance.

John


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[BlackBird_SR71]

On boosted engines, Use Coil Dwell table instead of Standard Dwell under Ignition and Trigger Wheel settings. Twin plugs and Coils per per Cylinder do not reduce the Dwell period required when under boost. Each plug is still subjected to increased Combustion pressures under Boost which increase the Flash over Voltage required.

You are still going to need 2.5 ms or whatever the Maximum dwell specified for the Coils is when under Boost. However, by using the Dwell Table, you can reduce coil dwell at low RPM's and Cruise. This is a common Coil cooling strategy used on OEM ECU's.

[BlackBird_SR71]

How much boost are you running, what plugs and what plug gap?

[Porsche930Targa]

I am running 1.1 bar (15.95 psi). Plugs are NGK BR8EIX resistor plugs. Gapped to 0.025".
How does this look for a boosted dwell table?

[BlackBird_SR71]

Not bad... but it can be improved upon. The low scale 20 KPA and 500 RPM figures can be eliminated and more resolution added in around Cruise

Edit: I would re-bin the Table with with a 30 45 55 65 80 100 120 150 Kpa Load. RPM go 1000, 2000,2500,3000 4000,5000,6000,6500 RPM Scale. Bump the Dwell at Cruise Load ( 55 to 65 Kpa ) and Cruise RPM ( 2500 to 3,000 ) to 2.0ms as needed. ( Lean cruise mixtures are harder to fire ) . I'd bump the 80 Kpa figures from 2500 RPM up a bit as well. 2.0 to 2.5 ms.

Don't worry about the Top end and the bottom of the tables being " Short " and going " Off Scale " MS will continue with the last setting on the Table when it goes " Off Scale ". So no need to eat up resolution on a small 8 x 8 Table by extending KPA too high. You need some more resolution in the middle of the Table to handle lean Cruise modes. That needs more spark energy.

I'll make up Dwell Map later similar that the Audi/VW guys run a bit later and post it. Heading out for dinner right now

[Porsche930Targa]

Thanks Blackbird Much appreciated.

[Porsche930Targa]

Here is my dwell battery correction table. My car has been running typically around 13 V. So it's adding 13% to Coil Dwell. Coil Dwell is set to 2ms. In the Datalogs it shows as 2.3ms
Which seems to correlate. So once in boost if I run 2.5 ms in table my actual coil dwell will be 2.85ms. Does this seem reasonable?

[BlackBird_SR71]

Seems perfectly reasonable. Most modern cars run between 14.0 to 14.3 v at Full charge rate. That's why the 100% ( zero compensation l) line is defaulted to 14.0 V.

A few of things I would check.

1: What year is your 911? You mentioned that your 911 normally runs at 13 v. Is this at idle or above 2,000 RPM? It should be at least 13.7 to 14.5 v. A check of your charging system may be in order. Older vehicles with external ( mechanical ) V/Reg's tend to be a bit weak on alternator side. If you have an older alternator with an external regulator and a lower amperage alternator, you may want to consider upgrading the alternator to a newer Internal regulator style with increased amperage. Besides having a more efficient and reliable solid state internal regulator, newer " small frame " alternators are also more efficient at idle RPM's. They can charge at full voltage at idle rpm's with a heavy electrical load.

I belong to Vintage Datsun 240Z groups and one of the first upgrades we do is get rid of the old weak, 45 and 50 Amp external V/Reg alternators and upgrade them to a 80 to 120 amp modern alternator with Internal V/reg's. Usually high output Mitsubishi's out of later Nissans or AC Delco one wire alternators ( That is a popular swap ) The difference is amazing. No more slow wipers, dim headlights or fouled plugs because of weak spark.

Bosch makes a lot of high output alternators that should just bolt on. Modern VW's have some very high output alternators. And they are usually a lot cheaper than getting them for a Porsche. I'm sure that Porsche forums have alternator upgrade articles, if you decide to go this route

Headlights and ignition system are tw0 things that are very sensitive to voltage drops. A 5 % drop in voltage can produce a 10 % reduction in light output ( Source: Daniel Stern Lighting ) . Same with ignition systems. You want a solid 14.0v when above 2,000 RPM... with full electrical load. Lights, wipers, defrosters or AC.

BPR8E-IX are fairly cold plugs and can foul at idle pretty easily. That may be your misfire issue after idling for a while. . Particularly if the charging voltage at idle is a bit low. I'm assuming air cooled heads... and that is why the 8's for only 1.1 Bar or Boost? . Most cars with water cooled heads can use 7's up to about 15 lbs of Boost ( 1.1 Bar ).

2: Reduce your cranking Dwell . 6.0 ms Cranking Dwell is too much IMHO. This only needs to be .5ms to 1.0 ms above running dwell. Remember that battery voltage compensation is still applied when cranking. So when the starter pulls the voltage down when cranking, you already have a compensation being added through the Batt Voltage table... on top of the increased Cranking dwell.

3: If the Denso coils are the high output ones that I think they are, you should be able to run a slightly larger plug gap. That will help reduce plug fouling. Your should be able to run .028" at 15 lbs fairly easily. Note: that is with a charging system that is fully up to snuff and outputting a solid 14+ volts above 2,000 rpm.

I also own a Turbo Audi and we have no real issues with using .028" plug gap up to about 20 lbs of Boost. Other than the crap reliability of the stock VW/Audi coils... which is another, rather long , story.

[BlackBird_SR71]

Here is a Dwell compensation Table based on Load that you may wish to consider. You don't need anything more than 150 Kpa or lower than 1,000 RPM as mentioned. TS will continue with last value off scale. I made a couple of small changes from my earlier post:

Dwell Table-rev2.JPG

[Dennis930]

930Targa,

What is your idle AFR? These engines like 13.5 - 13.8. Some people run them at 14. If you are too rich it might fouling the plugs at idle. I am using the same plugs, no fouling issues.

[Porsche930Targa]

930Targa,

What is your idle AFR? These engines like 13.5 - 13.8. Some people run them at 14. If you are too rich it might fouling the plugs at idle. I am using the same plugs, no fouling issues.

Hey Dennis

I am running 13.8 Afr. Seems happy enough. I have been playing around with injector timing table. It has really made a difference in my cruise maps. Lower values on VE table.

. I struggled a little with getting the sequential working I ended up ordering a new hall sensor from DiYautotune. Car fired up full rpm sync no cam error.

Really liking the MS3 Pro


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[Porsche930Targa]

Here is a Dwell compensation Table based on Load that you may wish to consider. You don't need anything more than 150 Kpa or lower than 1,000 RPM as mentioned. TS will continue with last value off scale. I made a couple of small changes from my earlier post:

Dwell Table-rev2.JPG

Thanks Blackbird this information is really helpful.
I appreciate it.


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[fast930]

I also have been running 12 desso cops for a few years now. I have always left the dwell at 2.5 and am running decent boost yielding 700 rwhp. Is there any advantage other than a slightly better idle? I am also running a 160 amp alternater, maybe that's why my idle is fine. Are you running e-85? The stuff was made for air cooled cars, after you swap out the 25+ years of old hoses.

[Porsche930Targa]

I also have been running 12 desso cops for a few years now. I have always left the dwell at 2.5 and am running decent boost yielding 700 rwhp. Is there any advantage other than a slightly better idle? I am also running a 160 amp alternater, maybe that's why my idle is fine. Are you running e-85? The stuff was made for air cooled cars, after you swap out the 25+ years of old hoses.

Idle quality is good. Although I have to change to a warmer plug, I have a slight miss.
A higher amperage alternator is on my wish list.
I live in Canada, and E85 is not readily available, where I am. I run a 94 octane gas.
I plan on replacing fuel lines this coming winter.


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