which spark plug is more important?
 

i recently changed around the ignition system in my IT-7 car (first gen with a 12a). before i had a single MSD running the oem coils firing both plugs at the same time. ran great. i found a crane hi-6 and coil in my garage which i have now hooked up to run the trailing plug, using the msd and an oem coil for leading. timing is set to 24l, 16t (all advance mechanisms have been disabled). i assume the hi-6 is putting out a more potent spark as its a much newer box and is also using an aftermarket coil. the only reason i decided to put it on the trailing plug is because on the 2nd gen the trailing coil is significaly larger then the leading. i figure mazda must know what there doing so i rigged mine the same way.

anyone have an opinion on which plug should get the hotter spark?

http://russmarshall.com/albums/it7/ignition.sized.jpg

all advance mechanisms have been disabled? The ignition needs to advance as the engine RPMs get faster. And if I had to have an aftermarket ignition on either the leading or trailing coils, I'd put it on the leading coils.

why? the mechanical and centrifugal advance only function below 5k rpm or so, above that there is really no change in advance as RPM climbs, since my engine never goes below 5k rpm so its really not needed. plus less moving parts = more reliability. to finish first one must first finish...

The leading plug does the bulk of the work in the engine. If you don't believe this, try running with your leading, and then your trailing coil disconnected. With the trailing coil disconnected, the engine should run more or less normally. With the leading disconnected, it should barely run. Also, if you've ever seen a housing, the leading plug is exposed to the chamber. The trailing plug fires through a small hole in the housing.

I suppose the only way to really tell for sure is to try it on both. I'd put it on leading, though.

-=Russ=-

well i was at the dyno all day, tweaking and tuning. i tried both configurations. there was no difference either way. oh well...

good news is im now making about 115whp with a stock port 12a, yippee....

Well, that's good to know! That's quite impressive on the power... congrats!

-=Russ=-