Ignition coils

[kevdachev]

I have just bought a M800 for my twin turbo small block chevy drag race truck. I would like some info on ignition coils. At present I have an MSD 6AL and single coil. I intend to boost about 15psi. Do you think my coil is man enough? I would like to use 8 MSD CHEVY LS coils and I know I need an ignition expander, but do you think I need this extra cost. Any help would be extremely helpful. Thanks

[AdamW]

A 6Al probably would have enough grunt but I personally would be going the CNP route to give a bit more headroom. You could do it without adding much cost; I wouldn't bother with an expander, wasted spark will be fine (wire two coils per output) and standard GM LS coils are relatively cheap. I wouldn't bother with MSD branded LS coils, just try to get genuine GM coils and avoid the cheap Chinese ones.

[kevdachev]

Adam, thanks for your reply but I am pretty new to ECUs and don't know what a CNP is or the pros and cons for this against an ignition expander.
Kev

[AdamW]

Sorry, CNP = Coil Near Plug. That's what a LS type coil is normally referred to as. COP = coil on plug. A M800 has only 6 ignition outputs so without an expander you have to pair the coils up and fire two together twice as often as they normally would. This is called wasted spark since you have a spark during the compression stroke and again during the exhaust stroke. The main disadvantage of a setup like this compared to an expander firing the coils sequentially is I don't think you can individually trim ignition timing on each cylinder, at very high rpm you can run out of dwell and you will have less aux outputs to use but I don't think any of these will be big deals for you.

[stevieturbo]

As long as you have a phase sensor, even in wasted spark you can trim individual cylinders.

At least you can with other ecu's

Even though it's wasted, the ecu still knows which cylinder is being fired at any given time, only difference is 2 coils receive the signal.

And as said, try and get genuine GM/Delco coils, not MSD.

Although Firecore are now re-selling some Pantera made IGN-1A drop in type replacements for the D585 coils which are supposed to be more powerful.
Not quite as powerful as the proper IGN-1A though

[Scott@FP]

Ignition expander will allow full sequential fuel, 4 channel waste spark will be semi-sequential (1 inj event per rev) or batch.

[AdamW]

Ignition expander will allow full sequential fuel, 4 channel waste spark will be semi-sequential (1 inj event per rev) or batch.

Scott, that's new to me and interesting to hear, although I haven't done a V8 for a long time (last was an M8...).
Are you absolutely sure that with an M800 you cant do a v8 with seq injection, in sync once per 2 revs mode, with waste spark ignition? Seems odd? ECU manager certainly accepts those settings like it would work...

Sorry to the original poster if my original comments weren't fully correct.

[Scott@FP]

You're correct, I'm coffee deficient as per usual. My bad. Don't know what I was thinking about.

Maybe 'turbo' makes me read 'staged injection'?

You DO lose 3 outputs vs the IEX, I don't think I've ever done an ECU that didn't use up damn near everything and think in those terms.

Another thing to consider if the engine can rev high enough and you're using inductive coils, waste spark may not allow enough charge time + recovery time at high RPM, 5-6mS dwell, waste spark and 8000+ RPM starts becoming incompatible, dwell times getting over 70%-80% can do damage to the driver circuits and/or coils, or if they are 'smart' drivers they can start current limiting and you lose spark energy without knowing it.

[stevieturbo]

Standard LS coils dont really need over 4.5ms, and certainly do not dwell the D585's over 4.5ms as they can fire prematurely above that

And at that dwell, they'll easily do 15...or 30psi boost on most engines.

8000rpm on a V8 wont post any trouble, although I'd doubt it is spinning that high.

[Sean]

dwell times getting over 70%-80% can do damage to the driver circuits and/or coils, or if they are 'smart' drivers they can start current limiting and you lose spark energy without knowing it.

Scott I have just stumbled across this, and it might explain something. This current limiting, would it apply to the Mercury Marine smart coil? I have seen them referred to as IGN 1A, but then there seems like there's aftermarket stuff called that as well?

Thanks