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bob cook
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PostPosted: Fri Apr 25, 2008 2:16 pm    Post subject: plug gap Reply with quote

I have a 1915 dual kadrons svda dist with compu fire bosch plugs what gap should I be setting plugs at thanks
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Matt Wilson
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PostPosted: Fri Apr 25, 2008 4:32 pm    Post subject: Reply with quote

.028 is fine
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A.J.Sims
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PostPosted: Fri Apr 25, 2008 4:35 pm    Post subject: Reply with quote

.0279" or .0281" but not .028" Very Happy
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PostPosted: Fri Apr 25, 2008 5:30 pm    Post subject: Reply with quote

since we're on the subject... what is the spark plug gap if you're running a turbo? i've been told to make it closer, but was never told how much closer.

thanks in advance.
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A.J.Sims
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PostPosted: Fri Apr 25, 2008 6:48 pm    Post subject: Reply with quote

.023 to .028"
i like .027"
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1955ccbug
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PostPosted: Sun Jun 08, 2008 1:45 pm    Post subject: Reply with quote

I'm running a 010, pertronix module and a compufire 35,000 volt coil..what should I gap the plugs to?...W8CC Bosch plugs. How does plug gap affect the running of the engine?
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shegel
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PostPosted: Sun Jun 08, 2008 2:02 pm    Post subject: Reply with quote

what is a good upgrade plug for these 1600 motors. ngk iridum double plat autolite. plat ngk?
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PostPosted: Sun Jun 08, 2008 3:23 pm    Post subject: Reply with quote

1955ccbug wrote:
I'm running a 010, pertronix module and a compufire 35,000 volt coil..what should I gap the plugs to?...W8CC Bosch plugs. How does plug gap affect the running of the engine?



The same as stock, .028.

shegel wrote:
what is a good upgrade plug for these 1600 motors. ngk iridum double plat autolite. plat ngk?


Stock Bosch W8AC, W8AP if you want platinums, or NGK B5HS. You wont notice any improvement using a more expensive plug on a stock 1600.
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PostPosted: Sun Jun 08, 2008 11:07 pm    Post subject: Reply with quote

I find that .028 may potentially misfire if your engine has alot of carbon buildup. The junk carbon may get trapped between the two electrodes.

Having a gap of .035 shouldn't be an issue. The larger gap may benefit you if you have an aftermarket coil that can potenially create more KV. The likelihood of even getting close to the max potential of your coil is next to nil unless you like arcing your sparkplug wires an inch or two away from ground Smile

Your engine will determine how much KV it will demand. Gap of plugs, amount of a/f mixture, compression etc. Just remember its more difficult for the engine to burn a lean mixture than rich. This will "make" the ignition system work harder (ramp up KV) to burn the fuel mixture.

You "may" find a larger gap to run smoother. It really depends on your setup.
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V-Dubin65
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PostPosted: Thu Mar 12, 2009 11:49 am    Post subject: Reply with quote

I'm running a 2276 with 44idf's ,CB 044 9.5:1 -10:1 CR with the NGK d8ea and a compufire coil pack with 60-70,000 volts....so should I gap at .035? Any input would be very helpful,Thanks.
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PostPosted: Thu Mar 12, 2009 12:16 pm    Post subject: Reply with quote

im running a 1776 with a progressive and an svda with pertronix and pertronix 60130 60k hv-e coil, with ngk projected core bp5hs plugs gapped at .35 and it runs good. should run even better if i ever get the blasted carb dialed in Brick wall
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PostPosted: Thu Mar 12, 2009 12:28 pm    Post subject: Reply with quote

of course if you had a JACOBS SUPERCALIFRAGILASTICEXPIALIDOCIOUS ignition system............. Dancing Laughing Twisted Evil

sorry guys had to!!!!!! haa haa haa

hi scott Smile
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PostPosted: Thu Mar 12, 2009 2:04 pm    Post subject: Reply with quote

I'll stick to my wimpy Ford Tempo waste spark ignition, it seems to fire a 1915 turbo with .030" gaps just fine.
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The Noof
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PostPosted: Thu Mar 12, 2009 2:41 pm    Post subject: Reply with quote

miniman82 wrote:
I'll stick to my wimpy Ford Tempo waste spark ignition, it seems to fire a 1915 turbo with .030" gaps just fine.

Amen...and I'm willing to bet it will light up .045" gaps just fine.
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PostPosted: Thu Mar 12, 2009 2:48 pm    Post subject: Reply with quote

bowtie56jw wrote:
im running a 1776 with a progressive and an svda with pertronix and pertronix 60130 60k hv-e coil, with ngk projected core bp5hs plugs gapped at .35 and it runs good.

If you actually gapped your spark plugs at 0.35" you'd have severe crossfiring inside your distributor cap.

Your engine likes the biggest possible spark plug gaps that your ignition system is capable of firing.

But even if you are using a Jacobs ignition system, you are still limited by the terminal spacings inside the distributor cap.

A resistor rotor, resistive spark plugs wires and resistive spark plug boots and resistor spark plugs all cause the voltage inside the distributor cap to become even higher which limits the maximum spark plug gap that you can use. Which is of course why you should use a resistorless rotor, low loss magnetic suppression ignition wire and resistorless spark plugs.

The voltage required to fire the spark plugs is primarily dependent on the spark plug gap and the fuel mixture density. If you increase the compression ratio, it takes a higher voltage to fire the spark plugs. If you improve your volumetric efficiency it also increases the voltage required to fire the spark plugs.

The following table is a VERY rough guide to the maximum spark plug gap versus compression ratio that a small cap Bosch distributor can handle before crossfiring or arcing to the distributor body occurs within an otherwise stock engine, when using standard NON-resistor copper core spark plugs with standard electrodes, magnetic suppression igniton wire, and a resistorless rotor. Whether or not your ignition system can fire spark plug gaps this wide is another matter. There may not be much safety margin with spark plugs this large. If you substantially improve your volumetric efficiency you may need to reduce the spark plug gaps further.
Code:
Maximum Spark  Compression
Plug Gap       Ratio

0.050"         7.0:1
0.047"         7.5:1
0.043"         8.0:1
0.041"         8.5:1
0.039"         9.0:1
0.037"         9.5:1
0.035"        10.0:1
0.033"        10.5:1
0.031"        11.0:1


bowtie56jw wrote:
of course if you had a JACOBS SUPERCALIFRAGILASTICEXPIALIDOCIOUS ignition system............. Dancing Laughing Twisted Evil

If you actually had a Jacobs ignition system you could fire any width spark plug gap that the tiny Bosch distributor cap can handle.

Jacobs ignition systems are still selling for bargain prices on ebay. Last week an Jacobs Omni-Magnum sold for $28.00. That the igniton coil and ignition system in one package.

For the record, the advertised ignition coil voltages are pretty much MEANINGLESS numbers as they are usually measurements taken WITHOUT a spark plug load.

Voltage specifications only have meaning if they tell you what load resistance was connected to the output of the ignition coil when they measured the voltage.

A new spark plug in an engine in good condition with the correct air-fuel ratio has a load resistance of about 1,000,000 ohms.

In and extreme engine, or with spark plugs that are beginning to foul, the spark plug load resistance is around 500,000 ohms.

And if you really want to find out what the ignition coil is capable of, use a 250,000 ohm load as well. Connect each of these three load resistances to the output of the ignition coil, and then see what the maximum voltage the ignition coil can develop to fire a spark plug, and it will tell you much of what you need to know about an igniton coil.

A turns ratio of 1:60 is excellent for a small cap Bosch distributor. Turns ratios much larger than about 1:90 actually degrade the performance of the ignition coil and are only useful for selling to ignorant customers that don't realize that bigger isn't always better.

Scott Novak


Last edited by Scott Novak on Sun Mar 15, 2009 9:37 am; edited 2 times in total
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PostPosted: Thu Mar 12, 2009 3:07 pm    Post subject: Reply with quote

The Noof wrote:
miniman82 wrote:
I'll stick to my wimpy Ford Tempo waste spark ignition, it seems to fire a 1915 turbo with .030" gaps just fine.

Amen...and I'm willing to bet it will light up .045" gaps just fine.




It does, but there's a caveat.

It works better at high RPM with a rich mixture this way, but for cruise conditions a smaller gap is what it ended up liking best. I run AFR's in the 16~17 range at times, and it misses with anything more than a .030" gap. It really depends on the engine, because head chamber, compression, intake and exhaust all play a part. What works on my engine might make yours run like poopoo.

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Makes the Engine forums much easier to read this way. Cool
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wardvwracer
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PostPosted: Thu Mar 12, 2009 6:19 pm    Post subject: Reply with quote

Scott Novak wrote:

The following table is a VERY rough guide to the maximum spark plug gap versus compression ratio that a small cap Bosch distributor can handle before crossfiring or arcing to the distributor body occurs within an otherwise stock engine. Whether or not your ignition system can fire spark plug gaps this wide is another matter. There may not be much safety margin with spark plugs this large. If you substantially improve your volumetric efficiency you may need to reduce the spark plug gaps further.

Code:
Maxium Spark  Compression
Plug Gap       Ratio

0.050"         7.0:1
0.047"         7.5:1
0.043"         8.0:1
0.041"         8.5:1
0.039"         9.0:1
0.037"         9.5:1
0.035"        10.0:1
0.033"        10.5:1
0.031"        11.0:1


Scott Novak


Scott,
Curious about this information. What's your source?

I've been trying to understand the "art" around spark plugs for a few years now. The hole mess of determining heat ranges, plug gaps, etc..., it leaves me confused.

In my race engine with 12 to 1, I've run between .035" and .045" with no noticeable change. Granted, I don't have easy access to a dyno, but SOP results didn't tell me anything. HEI ignitions in GM products that I used to work on ran .045". So I figured my MSD ought to be able to run a wider gap. Well, since I didn't feel any difference I went back to the .035".

Heat ranges have confused me as well. Then there's the question of does a colder plug need a tighter gap? Would a hotter plug, with a hotter spark, benefit from a wider gap for a more complete burn? Confused
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PostPosted: Thu Mar 12, 2009 8:28 pm    Post subject: Reply with quote

I have a basic 2.0 T-4 in my bug and have been running .045 for years with the Jacobs bugpak and a Mallory Unilite.

I was told by Jacobs as long as my wires can take it I can go to .055, Running NKG plugs.


I would get a shock with the Blue Coil and give a yell, with the Jacobs it felt like my arm was hit by a baseball bat.

The Mallory is wide enough spaced, I don't see any problem in the biggest spark you can get.

Jacobs says just keep opening up the plugs till you do not see any improvement.

The only problem with very wide gaps is if the Jacobs fails and you put back a stock igniton, you have to go back to .027 and pull all the plugs or the car won't start.
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PostPosted: Thu Mar 12, 2009 9:58 pm    Post subject: Reply with quote

wardvwracer wrote:
Curious about this information. What's your source?

My own experience and finding out what spark plug gaps and compression ratios that other people have been able to use without crossfiring problems, as well as some calculations. The table is by no means absolute. You may be able to push the spark plug gap size a little further if you are willing to reduce your safety margins within the distributor cap.

Heat range is fairly simple. Use the coldest spark plug that doesn't foul. Anything hotter just increases the chance of pre-ignition.

You need to remember that the fuel mixture density within the spark plug gap is the single biggest determiner of the voltage required to jump the spark plug gap.

wardvwracer wrote:
Then there's the question of does a colder plug need a tighter gap? Would a hotter plug, with a hotter spark, benefit from a wider gap for a more complete burn? Confused

If you use a hotter spark plug, the fuel mixture density inside the gap will be slightly less and the voltage required to fire the spark plug gap will be slightly less. But as long as your spark plugs aren't so cold that they are fouling and your ignition system is capable, changing the heat range won't affect the burn significantly, unless the heat range is too hot and you have pre-ignition.

If you advance the spark timing, the spark will occur at a position in the cycle with less cylinder pressure, resulting in lower a fuel mixture density within the spark plug gap and the voltage required to fire the spark plug will be less.

The point is that if you are at the limits of your ignition system and you make a change, it could possibly cause an engine condition where your ignition system was incapable of firing the spark plug gaps, or it could push your distributor cap past it's limits and you could have an arc-over to the distributor body resulting in misfiring.

You need to keep this in the back of your mind when trying to interpret the result of any engine changes that you make. Did retarding the spark timing actually cause engine to start missing, or was it fact that you exceeded the capability of the ignition system that caused the problem?, etc.

A stronger ignition system will be less susceptible to fuel mixture extremes and you won't need to jerk around with your fuel mixture as much to get the spark plugs to fire reliably. Jacobs claimed to adjust the spark output of their ignition systems to provide the ideal spark intensity under all engine conditions. It don't know if that still applies to the newer oval shaped Jacobs ignition systems.

When you have determined your final engine configuration and ignition system, the main variables left will be spark plug gap, fuel mixture and spark timing. A wideband O2 meter can easily help you adjust the fuel mixture accurately. Then it's a matter of adjusting the spark timing and spark plug gaps. Increase the spark plug gaps until you notice a loss of performance, and, or gas mileage.

wardvwracer wrote:
In my race engine with 12 to 1, I've run between .035" and .045" with no noticeable change. Granted, I don't have easy access to a dyno, but SOP results didn't tell me anything.

Sometimes it's difficult to tell but the SOP method. That's why it's also a good idea to keep track of gasoline mileage. Also keep in mind that increasing the spark plug gap has the effect of advancing the ignition timing. Sometimes you may need to retard the spark timing slightly to obtain the correct ignition timing.

Dynamometers are invaluable for any kind of engine testing. For most of use that can't afford dyno time, keeping track of gas mileage, and measuring acceleration times can tell you a lot. If the engine has any problems like hesitation, pay attention to whether increasing the spark plug gap has any effect good or bad. Pay attention to how smooth the engine runs. Do you notice any missing under any conditions, etc. If you have access to equipment to measure pollutants emissions, see if the spark plug gap has any effect. Reduced hydrocarbon emissions are a pretty good sign of improved efficiency.

Scott Novak
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PostPosted: Thu Mar 12, 2009 10:24 pm    Post subject: Reply with quote

just ribbin ya scott Laughing
nope no crossfire and gap is .35 i even put the 3 prong spade connectors on the new pertronix coil off my bosch cause i run the choke off it. yeee haaaaa #2gunfire Dancing

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