Ok, this is prob going to make me feel like an idiot but for some reason I cant wrap my brain around it right now......

On a FD the leading coil is double post and runs both L plugs. Do they fire at the same time? The reason I ask is doesnt the exhaust blow out at different times? If that is so how is it combusting the fuel at the same time??? Also the T are running off seperate but weaker (or so I've been told)coils. If the leading fire off at the same time then should the T also fire at the same time? If this is the case why not scrap the 2 weaker coils and use on L coil in its place to provide that much more spark?

I guess my mail question is does the L plugs fire at the same time and if so how since the exhaust comes out of the ports at different times? Or am i wrong about the exhaust coming out at different times?

Thanks,
STEPHEN

 

Yes they fire at the same time.

They can do this because when one rotor is at TDC, the other rotor has one apex seal at the pinch of the epitrochoid - between leading and trailing. It's no problem to fire the leading plug at what is the end of the power cycle, in fact it helps emissions just a little bit.

You cannot fire trailing at the same time for the same reason - when one rotor is at TDC the other rotor has an apex seal at the pinch - trailing plug is exposed to the beginning of the compression cycle. NOT the time to be seting off any loose sparks!

I accidentally put my distributor in 180 degrees out of phase, which has the same effect - trailing plug fires 180 degrees too early. What happened was detonation at anything over about 1/3 throttle - on a vacuum scale I guss it'd be around 10" of manifold vacuum.

 

So basically every time the L sparks only one of them is needed and the other is wasted. Would it be possible that if your timing was real retarted the wasted spark could fire during the beginning compression phase, say the apex seal has already moved past the pinch of the epitrochoid and the L is now opened up to the compression cycle. Is that possible??? Would that be the same as you putting your dist in out of phase? I dont know much about dist, I've only messed with a 3rd gen.

Thanks for all the info, its very helpful

 

Yes that is possible, but it'd have to be REALLY retarded, like 30degATDC or more...

 

Do you think that over a period of say 60000 miles worth of rpms that spark hitting the apex seal would make it weaker??? Ok, in one rpm the L fires 6 times right (I'm asking but I think its right). That means at 3000 rpms the L coil is firing 18000 times a minute. This means that since 1/2 of those sparks were fired right onto the apex seal its taking a **** load of abuse from that. Surely that has a bearing on its life and making it weaker, I mean there is no telling how many millions apon millions of times its getting hit by elec current.

Why not fire them seperate??? To hard to configure and tune???

STEPHEN

 

Yes, that’s why this method is called “wasted spark”! This has been common in EFI cars for many years. Look under the bonnet of some EFI cars and you’ll see double ended coils in most of them. The apex seal is between the plugs when the wasted spark fires, not right on it. No probs. Cost mainly. One double-post coil costs less than two single-post ones, and it halves the number of ignition drivers required in the ECU. It also simplifies tuning because you’re only doing half the work.