engine and drivetrain Plug Question -- Dumb

[Guest Anonymous]

What exactly will opening up the gap on my plugs do for me?

I've got a stock, tired engine. New tii dist, and 8mm plug wires. I'm running what I think is 32mm for my plug gaps (NGK). I'm wondering if I'll notice any difference at all if I go to a higher gap.

Thanks.

[Guest Anonymous]

Without an electronic ignition, opening the gap will make the plugs foul faster, as the spark will have a greater distance to travel thru oil mist. Bottom line, you'll get a misfire faster with a wide gap on a worn engine, unless you have a hotter than stock spark.

[Guest Anonymous]

I believe I am running stock gaps...

All advice appreciated... course, I will go out and play regardless!!

-Jason

[Guest Anonymous]

Probably won't hurt anything, then. My '69 has a pretty thirsty #4 cylinder--plug gets pretty cruddy quick. I run .035 gap on the plug (vs .025 stock) with an old Delta Mk 10B capacitive discharge (CD) ignition system and the plug always fires.

Try it, see what happens...

Cheers

Mike

[Guest Anonymous]

On a stock engine, much less a stock tired engine, the tii distributor and the one sold as a replacement by most parts houses actually provides a less-than-optimal advance curve. You could actually make a bit more power and econ with the vac-cannister-advance-only unit from an earlier car. The curve on the tii and replacement units isn't suited to the lower compression engines, period.

Sam

[Guest Anonymous]

32mm gap? Wow. That's a big gap.

Guessing that's a typo. On anything other than a boosted or multiple spark setup, opening up the gap simply means it takes more voltage to jump that gap - known as arc-over voltage. Stock systems have certain gaps specified because they're the greatest gap the system will take in that particular configuration - open it up beyond that, and yes, you open yourself up to the spark not always being able to jump the gap.

Incidentally, at 17,000 volts compared to 22,000, the blue coil is a LESS powerful coil than the stock black one. Why everyone seems to think differently is beyond me. It's originally intended as a low-power upgrade unit for air-cooled VWs. I'd switch to a stock or red unit. Bosch parts books back this up. Email me if you want the evidence

Pertronix doesn't boost the spark, it merely makes it somewhat more accurate by eliminating flutter and bounce inherent in a mechanical trigger (i.e., points) system.

With that system, I wouldn't open the gap up, I'd leave it stock. You're really not getting a more powerful spark than stock, as is.

Sam

[Guest Anonymous]

Seeing as the red coil puts out some 26.5KV of juice, compared to the stock 22.5KV, I'd take the stock gap (.024 to .028 in) and open it up a VERY small amount (no higher than .030, though probably you should just stick with the upper end of the specified stock range - .028 - and leave it at that.)

One of the advantages of having a hotter coil means that you've got more reserve voltage available to fire plugs when conditions are less than ideal. Use more of that reserve voltage to fire plugs with a wider gap, you're not necessarily going to make more power or get better economy - but you HAVE increased the chance of a misfire, and you've suddenly got a smaller margin of voltage available to fire those now wider-gapped plugs should they become dirty, or what have you.

Honestly, unless you're running a highly accurate crank-triggered, boosted, multiple spark setup, you're not really going to see a great deal of gain (usually not really even a little) from opening up and messing around with plug gaps. Saying "this gap works for such and such setup" is really kind of bogus - it depends on how much blowby you have in your engine, what your cylinder pressures are like, where the plugs' electrode faces are indexed in relation to combustion chamber, how dirty the plugs run on a normal basis, what heat range plugs you run, what shape your ignition system is in as well as how modified it is.

Most of the easy upgrades, like coils, plug wires, HD points, the Pertronix - they all serve to give a more consistent and only SLIGHTLY stronger spark. For a real boost in spark and thus a noticeable difference in power, I'd go with Electromotive's crank-trigger setup (really cool completely adjustable ignition curve - if you've ever seen anybody fiddle around with a laptop and advance curves while driving, it's not to be missed) or the simpler MSD or Crane units.

So the short answer? If you really wanna mess with it on only a mildly upgraded system, go ahead - but don't expect noticeable changes for the better. Open it up a tiny bit at a time, until things begin to get worse, back it off, and then see what plug life and reads are after that. You may or may not have learned something

Everyone's engine is different - and only a dyno can answer what the perfect plug gap is for your exact setup and power.

Ignition theory's actually pretty interesting stuff. I can recommend a really cool (though technical) Bosch book on the stuff if you'd like.

Just my opinion.

Sam

'76

points (they were cheap, ok? Being in college takes a bite sometimes), Red coil w/resistor, 8mm wires, tii distributor (9.5:1 compression, though)

[Guest Anonymous]

its almost a waste of money since the coil will only

send enough voltage to jump the gap. The gap determines how many volts are needed to arc across.

[Guest Anonymous]

That's basically what I said - that, and try it if you feel like it, as *everyone's needs are different*. I run gap a bit wider than stock, but not by much.

Sam

'76