intenseapple

Pretty simple issue that I know how to solve but want to understand more about how/why it is happening in the first place. Motor is a built 1.9 with 8.6:1 CR, one step colder NGK plugs, and LS coils. To be specific on the coils, they are not ones often used with miatas or other aftermarket coil setups -- They are a D581 coil pulled from 4.8, 5.3, and 6.0 Chevy trucks in the mid 2000s. Not a lot of info out there about them but they seem fairly similar to the more common D585 coils that are used more often here. Dwell table from a was pulled for D585s. I am having a spark blowout issue under high RPM (> 4000) and load (> 16-17PSI). I gapped the plugs down to 0.030 and that significantly helped, but a few high-load misfires have still stuck around. I'm fine gapping the plugs down further and/or adding a tad more dwell, but it seems as though 0.030 is already a little low for an LS coil setup that is properly configured. All of the spark plugs are clean and free of damage. Any thoughts in the cause of this problem?

deezums

iTrader: (3)

Don't know why you'd think those coils are any good, but from what I remember they are crap with about 1/4 of whatever the discharge energy of the d585 is.

They are nowhere near the same size coil, they have less copper in them, they weigh nothing similar. They probably need longer dwell to get the same output and it's probably not even possible or wise to try and do so anyway.

I know really nothing about those coils other than they suck, if they have the same auto-discharge "feature" the d585 has then running the d585 dwell might be risking your engine. You could measure the current to figure dwell, or you could try and find the proper values out of a GM ECU.

intenseapple

Not to doubt the expertise, but do you remember where you learned anything about them? I can't find any details online aside from a few LS forums that claim they are very similar to LS1 coils. Unfortunately eh D585 has a different mounting bracket than the D581 or I'd just switch and call it a day.

deezums

iTrader: (3)

From some megasquirt page you yourself could probably find on google if you tried. It also has a calculator for calculating spark energy off max spark gap.

"Even compared to the LS1 coil, these are just crushers! On the LS1 coil there is around 40 milliamps of peak secondary current with 5 milliseconds of dwell time. On the LS2/truck coil (AC Delco D585), there is 120 milliamps!"

Or any of the millions of threads on LS1tech of dudes ripping out LS1 and the shitty truck coil for the "LS2" stuff.