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Old 06-15-2009, 04:32 AM   #1 (permalink)
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Has anyone done spark plug gap tests?

I've done some searching and see most people try to dabble in iridiums or other "upgrade" plugs. I've personally always stuck with plain old coppers; they've always worked best. It also helps I've got a simple 8v i4, so spark plugs are a quick 5 minute job.

For the 80's vw's, gap spec is 0.028 +/- 0.004. California spec is 0.028 + 0.004.

For pretty much as long as I've been changing out plugs, I've gone with bosch coppers, and kept the 0.032 gap, since in theory, that should be best?

But on a current car that I've been tuning up (1990 vw fox, ke-jetronic), I've killed off all vacuum leaks; pulling almost 20 inches at idle. Full ignition tuneup. MSD Blaster 2.

Before the tuneup, car had some old bosch platinums. I'm not sure of the gap. Don't have a tool at the moment.

But after swapping in the coppers, the idle is noticeably lumpier. Still trying to fix a lean running problem as well, so I'm not putting it specifically on the spark plugs (failed smog two times in a row now. insane NOx, but that's another story, not related to this topic..)

So taking this application as an example, has anyone tried say 0.024, 0.028, 0.032, 0.035, 0.040, 0.044?

I had a 1991 vw fox; pretty much the same car, albeit with digifant management. I've also used bosch coppers on that one, and after 20k miles or so, when I goto change the plugs, I'll often find the plugs have worn down / been blown out to 0.035-0.044 easily.

What's the response to different gapping? I haven't checked to see what color spark I get, but I can't imagine it being anything short of blue, since coil, wires, cap, rotor, and plugs are all new, and I added an additional ground strap to the valve cover.

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