it doesn't directly relate but if you're paranoid about the trailing you'll love this.

If you go to a 2nd gen coil or some other such setup that gives you wastespark on the leading, many on the haltech and single turbo sections seem to think that at higher power and RPM the later leading pulse is busting apex seals.

There has been quite a discussion on converting to eliminate the wastespark. I'd be more concerned with this than trailing plugs

Wow I'm glad I came across this.

I am planning on making a DFLDIS system and am planning to eliminate the trailing ignition when I do.

I figure the wasted spark, which fires into the exhaust cycle, will act as the trailing did and clean up the trailing edge of the rotor.

I'm no genius but I think having the leading plug firing twice will work better than having two plugs firing once... at least it should keep the leading plug cleaner ;)

I figure there's got to be some compelling engineering reason that Mazda continues to spend the money required for a dual-plug chamber with separated timing. I just wish I knew for sure what it was. It'd make me feel more comfortable about experimenting.

Doesn't seem like 'emissions' is an adequate argument when cats are as good as they are now.

Emissions is still a big argument. Regardless how good the cat is, the engine must run very near stoichiometric for the cat to function properly. If the engine is dumping loads of unburnt fuel with every combustion event, the cat won't be able to clean it up.

Fuel economy is big, too. OEMs spend a lot of money and effort on improving it. Unfortunately most options are a trade-off: "It gets us 2 MPG, but those hard, skinny tires look stupid and don't corner well." When there's something available that isn't a compromise -- i.e. it improves economy without making something else significantly worse -- they jump on it.