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[porthole]

i hear ya. used to close gap to fine tune advance!

All right, I'll bite. How does changing the gap affect advance.

10 degrees before TDC is 10 degrees before TDC.

[porthole]

I have just always had better luck with the Autolites.

Many years ago when I use to run my 340 6 pak Dart at the track, the Autolites where the only plug that I had good performance with.
Everything else available at the time just wouldn't hold up to 4-5 runs a night.

[old wrench]

Many years ago when I use to run my 340 6 pak Dart at the track, the Autolites where the only plug that I had good performance with.
Everything else available at the time just wouldn't hold up to 4-5 runs a night.

I should have a set of the Autolite XP Iridium plugs in this week sometime, want to take them over to a company that does our ignition system rebuilds, they have a test chamber where they can raise the compression up while the plug is firing and watch the voltage, you can then change the gap to get a good firing voltage for the plug.

You may find this interesting:

Air/Fuel mixture:  Rich mixtures reduce the tip temperature, causing fouling and poor drivability. Lean mixtures increase both tip temperature and combustion chamber pressure, resulting in pre-ignition. It is important to read the spark plugs frequently while tuning after engine modifications, the spark plugs will help you achieve an optimum air/fuel ratio.
   Compression ratio/forced induction:  As effective compression ratio increases through engine modifications or forced induction, a colder plug using a narrower gap and higher ignition voltage is required.
   Ignition timing:   Advancing the ignition timing by 10° increases the plug tip temperature by approx. 70°-100°C.
   Engine speed and load:  Increases in firing-end temperature are proportional to engine speed and load. When consistanly traveling at high engine speeds or hauling, towing, or pushing loads - install a cooler plug.
   Weather: Temperature, humidity, and barometric pressure all affect air density and intake volume. Higher intake volumes result in leaner mixtures and hotter plug tips.

   Unless you are racing and need maximum performance under today's precise conditions, try to select a plug heat range that runs the plugs near the center of the normal operating range so that the plugs will be able to handle a variety of loads and weather conditions.


Dennis could answer the gap on advance better, if he will, but you know how those drag racers are, always have a few little secrets deep inside that little black bag that they wont let out hehehehe

[rednectum]

i will answer kinda----open or close your gap, run bike, read plug, observe timing mark on ground strap. under a magnifying glass, you can see the mark change after adjusting gap. very little, but a change indeed. or another way of looking at it, say it starts to fire at 10* but takes longer for a full kernel (spark dwell) vs a quicker full kernel. yep, this was showed to me by an old drag racer. around 1972 he had a twin carb knuckle that went through the traps at 112 mph, low 11 ET.

[porthole]

I don't buy it.

No matter what the gap - if the plug "starts" to fire at 10 degrees BTDC it "starts" to fire at 10 degrees BTDC.

Doesn't matter if the plug had a 1/8" gap or 1/4" gap, either way it will start to fire at the same time, take longer to clear the 1/8" difference but what are we talking about?

If the total ionization time is considered (beginning of spark to end of decay) and averaged and you try a reason a timing advance or retard relative to a theoretical setting, I believe you cannot measure it, in the realm we are referring to here.

I'll stick with 10 degrees BTDC is 10 degrees BTDC, whether you have a .028 or a .035 gap. The average time difference does not matter. Maybe in an 8000 horsepower top fuel car .......................

[vagabond6542]

I came from a electronics background. One of my experiences was dealing with lightning strikes and being able to measure the probability of a strike.

Spark plugs fall in that environment.
The gap will determine how much the coil voltage will be required to fire the plug. This is in a non pressurized environment.  At certain atmospheres, the spark can be literally extinguished.
So how hot or cold a plug should be in an engine that can produce a 10 to 1 compression?
Follow the manufactor's suggestion, but you can vary the plug a little with make, style, and make-up. And the engine will have longevity. On the issue of gap, the closer you bring the gap, Leaner mixtures will fire more readily.
On the issue of colder or hotter, if you look at the air space between the center conductor and the outer wall, the space will be bigger when the plug is colder, and the space will be smaller when the plug is hotter. That is why surface gapped plug run so hot.
You can change the core electrode to be any material you wish, some do better than others due to the ability of the electron transmission of the material used, i.e, copper, platinum , or Iridium.

I hope that I help.

[old wrench]

I don't buy it.

No matter what the gap - if the plug "starts" to fire at 10 degrees BTDC it "starts" to fire at 10 degrees BTDC.

Doesn't matter if the plug had a 1/8" gap or 1/4" gap, either way it will start to fire at the same time, take longer to clear the 1/8" difference but what are we talking about?

If the total ionization time is considered (beginning of spark to end of decay) and averaged and you try a reason a timing advance or retard relative to a theoretical setting, I believe you cannot measure it, in the realm we are referring to here.

I'll stick with 10 degrees BTDC is 10 degrees BTDC, whether you have a .028 or a .035 gap. The average time difference does not matter. Maybe in an 8000 horsepower top fuel car .......................

If you got 10 BTDC in a top fuel, you better duck, they is gona be rods, pistons and a crank shaft fly in all different direction weeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[rednectum]

ok guys, i had a little funnin. i really was told that by an old racer, and remembering that mags ran a gap around .018, i could see where he may have had a point.

BUT!, in todays world, the ecm controls spark dwell and i think closing the gap would probably hurt power on a well tuned engine.

man, i was hoping to get unbalanced stirred up with the post, but i figured i better fess up.  hope some of yall found a little humor???/

[Hoist!]

ok guys, i had a little funnin. i really was told that by an old racer, and remembering that mags ran a gap around .018, i could see where he may have had a point.

BUT!, in todays world, the ecm controls spark dwell and i think closing the gap would probably hurt power on a well tuned engine.

man, i was hoping to get unbalanced stirred up with the post, but i figured i better fess up.  hope some of yall found a little humor???/

Having fun on the Forum. What kinda crap is that? You know better Dennis. No fun allowed, or DSP for you!!!

Hey Don, I think Dennis deserves an invite! What do you think?

Hoist!

[Twolanerider]

Hey Don, I think Dennis deserves an invite! What do you think?

Hoist!

But he helps sooooooooo many people?

[rednectum]

is that what you yanks call smalltalk? 

[porthole]

If you got 10 BTDC in a top fuel, you better duck, they is gona be rods, pistons and a crank shaft fly in all different direction weeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

Now Now, I wasn't suggesting the fuel cars run that, only that in an 8000 HP engine maybe the average burn time between gap differences would amount to something.

Top fuel cars typically run between 6-7 to 1 CR and 55-65 degrees advance on the start, so why would 10 degrees be a problem, other than the engine probably wouldn't fire off before fouling the plugs?

[rednectum]

Now Now, I wasn't suggesting the fuel cars run that, only that in an 8000 HP engine maybe the average burn time between gap differences would amount to something.

Top fuel cars typically run between 6-7 to 1 CR and 55-65 degrees advance on the start, so why would 10 degrees be a problem, other than the engine probably wouldn't fire off before fouling the plugs?

but arent they running around 16-18 to 1 dynamic? here is something interesting---- a fuel dragster only turns about 500 revolutions from green light to shut down! hard to imagine isnt it?

[old wrench]

but arent they running around 16-18 to 1 dynamic? here is something interesting---- a fuel dragster only turns about 500 revolutions from green light to shut down! hard to imagine isnt it?

Yep but that is 500 super hard revolutions, with a cost of over 2k per second and gets about 15gals per quarter mile, I guess if you could let it coast to a stop the mileage would be a little better 

[rednectum]

Yep but that is 500 super hard revolutions, with a cost of over 2k per second and gets about 15gals per quarter mile, I guess if you could let it coast to a stop the mileage would be a little better 

if they lean out the midrange they could get better mileage.