You want to lose the whole cylinder when it comes to twin plugs and failure. One plug firing where they used to be two will often melt the piston due to detonation. Better to have it completely shut down.

Kenik,

I am not sure I follow you on this on, the twin plug uses less ignition advance than a single plug for a N/A motor. So how does having a single plug fail of two with less timing cause detonation?

You are typically running twin plugs to accomodate higher compression. In that case, its not a 1:1 comparison between the failure of a twin plug and timing angleson a single plug.

On one of my motors I switched out single-plugged 8.5:1 pistons for 10.5:1. The heads remained the same except with the new plugs machined in. On the dyno the twin-plugged motor had more hp and tq, and peaked with a little less timing than when it was single-plugged. But I suspect I'd see pinging if only one plug was firing with the higher compression, even if it is a bit retarded from where timing was set at 8.5:1.

I understood shutting down a complete cylinder if there is a failure is the right approach, for the aforementioned reasons. The challenge can be finding the right EDIS or other ignition unit that can fire both plugs simultaneously and consistently.

It is not possible with wasted spark solution, only with COP.

Thank you for filling in all the blanks I left, John!

I humbly disagree. Thats what I have on one of my cars. Adaptronic ECU, 2x Haltech triple-channel ignitors and a pair of Accel EDIS coil 6-packs.

Yeah, but not when you fire both plugs of one cylinder with a single coil, then you have weaker spark on one of them.

Isn't that why you use COPs with integrated igniters? IIRC, these act as their own coil?

You can't fire two plugs in the same cylinder with one coil.

I know that.
And in fact you can, just one plug gets less energy than the other.

Electricity takes the path of least resistance...so...unless it is a double ended coil...I would think that only one plug would fire.
Double ended coils are in fact two coils in one...with the ground in the centre of the assembly.
Some Harley bikes use this system...if you look at the coil under the seat...it has two wires coming out...(plug wires) and two feed wires (power and ground)...inside, the coil is divided into upper and lower to power the plugs.
Bob

Few years ago we dynoed a Mercedes AMG 5.5litre supercharged engine on the engine dyno (same as SLR McLaren engine only bit less boost) I installed and tuned the ECU + ignition system and we used four Bosch 2x2 wasted spark coilpacks on it (it has 2 plugs per cylinder, totalling 16 plugs, 3 valves per cylinder).

Just out of curiosity we set the plug wires so that each cylinder was fired by one coil and engine worked. We took out the plugs, put the on the wires and both plugs fired.

So, it works but due to the nature of wasted spark, you get weaker spark on one of the plugs (or both) because the balance is not fixed (on one cycle it can be more on 1st plug, next cycle more on 2nd etc).

Proper and best way is to fire upper row of plugs with one coil-pack and lower row with other.

P.S. The engine made 810 hp/1170 Nm @ 1 bar of boost (changed drive pulley), here's photo of it on the dyno: http://www.otter-ag.ee/files/AMG3.JPG

Safe, would you be kind enough to share your COPs' specs? Origin, part number would be of tremendous help.

TIA,
Ben.

Edit: whoops, just saw the info was already posted. Thanks for all the great information.

Sure,
Car: VW/Audi, 1.8/1.8T engine ~2001-2005
Part number: 06B905115R (might be superseded by newer version)

Connectors for the coils can be bought at VW/Audi dealers. Don't have the part numbers here now, but can probably find them.


Edit:

I posted partnumbers earlier in the thread I saw:

6, Coils: 06B 905 115R (R was the latest version at the time)

6, connectors (empty): 4B0 973 724

12, female spade connector pig-tails: 000 979 133 A

24, wire sealing grommets: 357 972 741 A

6, two-part plastic boots for connectors: 6X0 971 921 A

Everything can be bought from your local VW/Audi dealer.

Highly appreciated: thanks!

Ben.

My experience with coil pacs is very jadded,they fail often on BMW and VW/Audi vehicles and my research indicates engine heat is a major factor in the pacs failing.
Beru coils for instance have a high rate of failure on BMW cars for instance,my e39 has fizzed out 3 to date and the Bosch and other oem coils have a better rep.
Its not only just the coils,the extention piece (to the plug) on the coil fails also,a good indication is the amount listed for sale on ebay for ALL brands of cars using them:rolleyes::rolleyes:
I'am not sure if you would want to factor this failure rate in to the hotter running air-cooled engine,have they been proven over a reasonable period to say they are a worthwhile mod.
My 2 cents take it or leave it,cheers.

I'm not sure it's hotter in an aircooled 911.
In a normal engine they live their life in a pretty enclosed space, but in a 911 there is a constant flow of air through the heads and the engine bay temperature is pretty cool compared to a turbocharged Audi for example.
I'm not sure the environment in an air cooled 911 is any worse than what they are designed for.

In any case, if one break down its not the end of the world, you can get home on 5 cylinders (may be bad for the cat if you have one), or you can carry a spare for longer trips.

Yeah, with EFI one can just unplug the injector connector of the cylinder with failed coil and it will not do any harm to the engine, just less power.

Yes, some good points ,but do you carry a spare plug lead for a 911 in the glovebox,? most likely not,and try and trace a misfire in a coilpac it can be a nightmare,besides who wants to fuel wash that dead cylinder for the trip home:(:(:( too many cars made today have coilpack problems ) think thats the issue.

Did you even read the post I wrote regarding the exact issue? With occasional misfires the cylinder will not be washed with fuel.
There are many options for coils and as there are many COP's that fail quite often, there are many that are very durable.
I am not yet decided which direction I will take with my twin-plug motor regarding ignition yet, but I will consider VAG COP's (like on the V5 engines) and so far these have proved very durable. They are available in various lengths also.
I could always go with two Bosch 3x2 coil-packs and be done with it though it wouldn't be such a neat solution as having COP's.


http://i.ebayimg.com/t/VW-AUDI-PENCI...+5T6g~~_35.JPG