M&W Ignitions Multi-Channel CDI

[mysocal911]

Originally Posted by rdimarco

The Bosch twin coil 0221503035 recommended by Wayne at M&W has 2 separate coils in a single housing.

Used in the Porsche 964/993 inductive discharge ignition systems, with a $100 Bosch dual channel ignition amplifier.

[winders]

Originally Posted by David

It's a Pro-14 CDI. I'm not advocating using a 4-channel now since obviously a 6-channel is better and available but at the time there wasn't much else in a quality CDI. I did work with folks way more knowledgeable than myself to spec out the system and they felt it would work fine.

With that said, I don't see any issue driving 12 coils off a 6-channel CDI because you can wire it so that 1 coil is firing on a power stroke and the other coil is firing on an exhaust stroke. I would not wire two coils off one channel to one cylinder.

I looked at the docs for the Pro-14. It does not show a setup wiring more than one coil to one channel. Also, if you are using the 4 channel unit with 6 plugs, two of the channels are wired to two coils and two are wired to one coil, correct? If that is the case, two cylinders are getting full power spark and 4 are getting half power spark. Not good for consistent combustion in all cylinders unless you tune each cylinder individually (not likely).

Or, you are only using 3 of the 4 channels and each coiling is getting half power spark.....

[David]

I’m only using 3 channels.

The spark on the exhaust stroke encounters much less resistance than the power stroke so the power is not split 50/50.

[jac1976]

Originally Posted by winders

I looked at the docs for the Pro-14. It does not show a setup wiring more than one coil to one channel. Also, if you are using the 4 channel unit with 6 plugs, two of the channels are wired to two coils and two are wired to one coil, correct? If that is the case, two cylinders are getting full power spark and 4 are getting half power spark. Not good for consistent combustion in all cylinders unless you tune each cylinder individually (not likely).

Or, you are only using 3 of the 4 channels and each coiling is getting half power spark.....

“Well, I’m making 475 hp at the wheels at .95 bar so not too bad. One of these days I’ll put a 6-channel CDI on it but there wasn’t one available when I built the engine.”

[David]

Originally Posted by winders

I looked at the docs for the Pro-14. It does not show a setup wiring more than one coil to one channel. Also, if you are using the 4 channel unit with 6 plugs, two of the channels are wired to two coils and two are wired to one coil, correct? If that is the case, two cylinders are getting full power spark and 4 are getting half power spark. Not good for consistent combustion in all cylinders unless you tune each cylinder individually (not likely).

Or, you are only using 3 of the 4 channels and each coiling is getting half power spark.....

Sorry, a little brain fade on my last post: I am running 4 plugs off each channel so yes each plug is getting a little less than half the CDI power with the waste spark plugs drawing a little power. Certainly not ideal but the engine has run well for 12+ years with a few light track days.

[winders]

Originally Posted by David

Sorry, a little brain fade on my last post: I am running 4 plugs off each channel so yes each plug is getting a little less than half the CDI power with the waste spark plugs drawing a little power. Certainly not ideal but the engine has run well for 12+ years with a few light track days.

Four plugs off of each channel? Wow. Isn't the ignition unit designed for one plug off of each channel? If that is the case, you are at 1/4 the power per plug......

[David]

Originally Posted by winders

Four plugs off of each channel? Wow. Isn't the ignition unit designed for one plug off of each channel? If that is the case, you are at 1/4 the power per plug......

No, because waste spark. 2 work hard on compression stroke and 2 barely work on exhaust stroke.

[winders]

Ok. From what I have read, the wasted spark on the exhaust stroke takes about 12% to 25% of the energy required on the non-wasted spark on the compression stroke. It would seem that each plug is getting, at most, only 38% of the energy it would otherwise get if the plug had its own channel.