Coil on Plug conversion reliability?

[Joebloggs]

Having read several posts on other forums re stick coil conversion I have a reliability question.

Many people were converting car coil packs to cop's and at first it seemed to be the ideal way of replacing the ever ageing coil pack, only problem was the dwell time on the stock ignition was far to long for the new coil and after awhile they failed. People with aftermarket ignitions could adjust the dwell but for those of us with standard cdi's were stuck with the stock coils.

So has anyone had regular failures? anybody measured the dwell to see if there's a potential problem or am I just worrying tof much?

[Danm54]

My 1100W runs cop's and as long as they're wired in series as a pair they closely match the standard single coil.

 

At least thats what I was led to believe, fitted mine a couple of years ago and not had any problems so far, no issues in the wet either.

 

Swapped the DR over too and thats the same. 

[Joebloggs]

Thanks, could be the answer with another bike I'm working on which has some real space issues under the tank.

[zedhead]

A professional motorcycle electician told me that the mismatch between a standard ECU and the COPs would result in the COPs burning out after 'a certain amount of time', although that time period was not confirmed as being a matter of minutes, or years... Since then I've heard of lots of people who have simply replaced standard type coils with COP with, seemingly, no apparent issues.

I'm certainly tempted with COPs to give a little more room above the rocker cover for stuff, and to increase air flow over the engine too...

[Gixer1460]

15 minutes ago, zedhead said:

A professional motorcycle electician told me that the mismatch between a standard ECU and the COPs would result in the COPs burning out after 'a certain amount of time', although that time period was not confirmed as being a matter of minutes, or years... Since then I've heard of lots of people who have simply replaced standard type coils with COP with, seemingly, no apparent issues.

I'm certainly tempted with COPs to give a little more room above the rocker cover for stuff, and to increase air flow over the engine too...

Simple question - would you connect 4 Dyna Blue coils (0.7 ohm) to your standard ECU? Because effectively that is what you are doing with COP's.

Easiest way is just add a Bosch 2 channel Ign. Amplifier between the coils and ECU and it'll be mint! Any other way is underpowered COP's or potentially overheated / fried ECU.

[Oilyspanner]

Out of interest I measured the resistance through a pair of connectors going to a pair of coils on my cop converted bike, it was 2.5 ohms - which is fine for a Slingshot. I used early K series GSXR stick coils, more recent ones use low ohm coils. I've been very happy with the conversion, can't remember if I did it last year or the year before, really quick starting and very neat - no HT leads clogging up the space above the engine - saved 10oz too. Will let the board know if any problems occur, but the ecu should be happy with resistance value.

[Gixer1460]

I've got some of those and seem to remember they were about 1.2ohm individually? Are yours wired in series as that might explain your figure - but they'll be getting 6-7v only?

[Arttu]

Yes, there is a risk of frying the coils or ECU or both. Especially if you don't know what you are doing and just wire in some random coils without  proper checks and measurements. But on the other hand, with typical bike COP coils there is a good change it will work quite fine. That's a short answer

Then a bit longer backround story. There are some fundamental differences between older ignition systems using 3-5 Ohm coils and later ones using COP coils. The older systems usually don't control coil charging time (dwell), they just charge coil most part of the engine revolution. That results varying and relatively long dwell time. For example at 3000rpm dwell might be something like 15-18ms and at 12000 rpm maybe 3-4ms. Coils are then designed to work with that. Coil primary resistance limits the charging current on safe level, 3 Ohm at 12V battery voltage won't exceed 4A current no matter how long you charge the coil. Coils are also designed so that they need quite long dwell time to output full spark power. Downside of this simple system is that spark power will decrease within rpm (after some point) as the dwell time gets shorter. Also even maximum spark power is relatively low since charging current can't be increased much without burning coils or driver electronics.

To improve these shortcomings the later systems use coils with lower resistance and shorter charging time. Typical bike COP coil has 1-1.5 Ohm primary resistance and needs only 1-3ms dwell to reach full charge. To keep charging current and coil heating at reasonable level the ECU then must control the dwell time. So coil will get constant dwell time before each spark regardless the rpm. Typical peak charging current values for these coils are 6-10A, so clearly more than with older system. But since charging needs only small portion of the engine revolution the total current draw of ignition system is usually even smaller than with older systems.

So what happens when you pair these COP coils with older ECU? If you connect them in series and they happen to have resistance from higher end of the range, like 1.2 to 1.5 Ohms, the total resistance will be at acceptable level. For example two 1.3 Ohm coils will result 2.6 Ohm and 4.6A maximum current at 12V which is still probably fine for ECU that is designed for 3 Ohm coils. For the coils that current is a bit low so you won't get full spark power out of them. Though the spark might be still better than with original coils. On the other hand the coils are now getting charged at much higher percentage of time than they are designed for (like 80-90% vs. 10-30%) which may affect their reliability.

Then if you happen to get coils with sub 1 Ohm resistance or if you connect them parallel the charging current can get so high that the ECU will burn immediately.

So like said in short answer, the results may vary a lot depending on coils and other parameters. There is a risk to fry ECU or coils immediately or reduce their life expectancy significantly. But with little luck it may work just fine and reliably. Of course you can always replace the luck with some investigations and measurements

[Oilyspanner]

23 hours ago, Gixer1460 said:

I've got some of those and seem to remember they were about 1.2ohm individually? Are yours wired in series as that might explain your figure - but they'll be getting 6-7v only?

Hi G1460 - I followed the 'how to' guide in Practical Sportbikes. They linked each firing pair in series, with one coil feed wire going to the left connector of the left hand coil and the other feed going to the right hand connector of the right hand coil - the other two coil connectors are then linked. As I see it, coils don't mind their polarity and being linked there's a 12v feeding the circuit.  I'm no great electrical guru and it took me a while staring at the PS article to convince me to do the work. The engine seems to have a really clean spark from tick-over to the rev limiter.

Oily

[TLRS]

On 14-9-2016 at 7:19 AM, Arttu said:

Yes, there is a risk of frying the coils or ECU or both. Especially if you don't know what you are doing and just wire in some random coils without  proper checks and measurements. But on the other hand, with typical bike COP coils there is a good change it will work quite fine. That's a short answer

..

Thanks for that! Even I understood most of that explanation!

[alfiestorm]

I have just been reading through this topic and it has got me intrigued.

I run a Dyna 2000 ignition with dyna coils (green ones) and Taylor leads. Would there be any benefit from running cop's with the Dyna 2000 and would the dyna 2000 be up to the job of running them safely. Or stick with what I have.

 

Alf

[Arttu]

Dyna 2000 is designed to work also with 2 Ohm Dyna coils so in that sense it should be able to run COPs at least as well than stock ECU. I guess the benefit would be pretty much the same than when replacing the stock coils. Green Dyna coils are very close to the stock coils in the end. At least you would get rid of the plug leads.

[Joebloggs]

Seen some 98 GSXR600/750 stick coils, anyone used them, don't want to get them only to find they're unsuitable.

Any part numbers I should check?

Thanks

[Oilyspanner]

I'm pretty sure the early Suzuki stick coils and K series ones had the same resistance values, but the lengths vary - I stuck with the K ones because I knew they were the right length, were in spec etc -  also they were newer.

[Joebloggs]

24 minutes ago, Oilyspanner said:

I'm pretty sure the early Suzuki stick coils and K series ones had the same resistance values, but the lengths vary - I stuck with the K ones because I knew they were the right length, were in spec etc -  also they were newer.

 

24 minutes ago, Oilyspanner said:

I'm pretty sure the early Suzuki stick coils and K series ones had the same resistance values, but the lengths vary - I stuck with the K ones because I knew they were the right length, were in spec etc -  also they were newer.

Thanks, will keep on the look out for later coils.

[Madb]

1 hour ago, Joebloggs said:

Seen some 98 GSXR600/750 stick coils, anyone used them, don't want to get them only to find they're unsuitable.

Any part numbers I should check?

Thanks

The coil sticks you need are off k1 750 or k1 1000 onwards. 600 sticks too short normally.