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Thu Dec 03, 2015 7:13 pm

I know standard plug gap is .028 but if you run an electronic module instead of points can you gap them bigger for possibly better spark or just leave them at stock setting?

Thu Dec 03, 2015 7:20 pm

I would just leave them at .028, you could, if you wanted to have the gap slightly larger and still be fine.

Thu Dec 03, 2015 8:26 pm

Correct me if I'm wrong, but why do people gap their plugs at .028 when that's the gap for a fuel injected engine?

I gap mine at .024, like it says to do in my Bently (for carbureted engines).

Tim

Thu Dec 03, 2015 8:38 pm

LEave the gap at stock setting. A module does not create a hotter spark. IT only makes the turning on and off of the coil more accurate and constant. I set them at .028.

brad

Thu Dec 03, 2015 8:39 pm

I've always gone .025-.028, Muir Idiot Book.

Thu Dec 03, 2015 8:41 pm

I go by the VW manual, .028in gap.
This is for a carbureted engine. (68, 1500cc)

Fri Dec 04, 2015 12:27 am

My Bently is for 1970-through 1979. The gap adjustment is apparently different for the 1600 models. My bug is a 1600 DP. the car is a 1974, but the engine is a 1970.

The Bently says .028 for fuel injection, and .024 for carbureted engines.

However, I just checked my 1974 Owners Manual and it says to adjust the gap to .028.

Damn. I've been keeping mine, per my Bently, at .024.

What's up with that? Bently--or my Official Owner Manual?

My engine starts right up and runs fine. What would be the benefit of gapping the plugs to .028 instead of the .024 that I've always used?

I use NGK B5HS (if I remember correctly).

Tim

Fri Dec 04, 2015 9:44 am

I use the Bosch W145 spark plugs with the gap at .028in. I can't imagine that setting it at .024in would harm anything. My manual does state that you can decrease the gap to facilitate starting in cold weather conditions. If it runs fine, keep doing what ever has worked for you. My friend was a VW dealer mechanic from 1962 until 1988 and he gaps all his plugs for all air-cooled engines at .028in. That's interesting though that the Bentley manual contradicts the VW manual.

Fri Dec 04, 2015 3:54 pm

Tim - I don't know why the Owner's manuals always would say 0.028", but then the Service and Workshop Manuals (and, up until the 1970s, the Without Guesswork booklet) always said .024-.028". Me, I use the .025" bit on my gapper tools... always have.

-Andy

Fri Dec 04, 2015 6:24 pm

Glut, I use the .025, too. There's no .024 on my wire-type feeler gauge.

If .025 is good enough for you, it's good enough for me.

Tim

Fri Dec 04, 2015 6:42 pm

Tim Donahoe wrote: What would be the benefit of gapping the plugs to .028 instead of the .024 that I've always used?

I'd like to take a crack at erroneously explaining this one: The way I understand it, it doesn't matter if your ignition system is capable of generating 50,000 or more volts, if it only takes 10,000 volts to jump the spark gap, then 10,000 volts is all you're gonna get. By opening up the spark gap, you increase the resistance, thereby increasing the number of volts required to jump the gap. This, in turn, creates a bigger zap to light the fire. The question then, becomes a matter of how much zap do you really need, and how much zap can your ignition system deliver.

So, if you have a low compression, low RPM engine that really doesn't do much heavy lifting, you may only need an 8,000 or 9,000 volt spark to get the job done, in which case slapping on that monster coil and opening up your spark gap isn't going to be much benefit, at all. On the other hand, high compression screamers that see plenty of strip action might need two or three times that amount of juice, in which case a bigger gap and a high-powered ignition system are essential.

I say if 0.024" works for you, then run it! Personally, I run 0.028".

Sat Dec 05, 2015 10:45 am

Some topic discussions.....

Electronic ignitions (technically, electronic points) - provide a consistent ignition trigger as well as increased dwell. The increased dwell is where you might see a performance improvement. Dwell represents the "time" allowed for the ignition coil to "charge". This time is represented in degrees of rotation. The greater the number of degrees the more "time" available for the coil to charge. At idle, this time is not so critical since at lower rpms there is more than sufficient time to fully charge the coil. As the rpms go up, the angular time remains the same but the actual time (milliseconds) goes down. At higher rpms this could mean insufficient time (ms) to fully charge the coil. The longer duration provided by most electronic points represents more current in the coil output at higher rpms.

High voltage coils & Spark plug gaps - Higher voltages can jump larger spark plug gaps (higher resistance). For coils of less than 45KV you will find spark plug gaps below 0.030". Once you get above 45KV you can open to 0.035" or even as large as 0.045" in some cases. Larger spark plug gaps make for a more reliable ignition of the air-fuel mixture and necessary in higher compression engines (harder to ignite). Cylinder compression, air-fuel ratio and oil leaking into the combustion chamber all affect how easy it will be to ignite the air-fuel mixture. At higher rpms, the rated voltage of the coil may not mean as much because the reduced charge time (see dwell). So using mechanical points with a high voltage coil will result in performance decrease at higher rpms.

To summarize, a HV coil allows the use of larger plug gaps. To reliably fire these larger gap plugs at higher rpms you need more dwell time which can only come from electronic points or some type of dual-point ignition.

Sat Dec 05, 2015 7:28 pm

I found gapping my plugs at .024" my engines didn't idle as smooth as with the plugs gapped at .028".

Sat Dec 05, 2015 10:43 pm

missourimark wrote: I know standard plug gap is .028 but if you run an electronic module instead of points can you gap them bigger for possibly better spark or just leave them at stock setting?

If that is the only change you have made, I would say to leave the gap stock.

Sun Dec 06, 2015 2:14 am

ashman40 wrote:

Electronic ignitions (technically, electronic points) - provide a consistent ignition trigger as well as increased dwell. The increased dwell is where you might see a performance improvement. Dwell represents the "time" allowed for the ignition coil to "charge". This time is represented in degrees of rotation. The greater the number of degrees the more "time" available for the coil to charge. At idle, this time is not so critical since at lower rpms there is more than sufficient time to fully charge the coil. As the rpms go up, the angular time remains the same but the actual time (milliseconds) goes down. At higher rpms this could mean insufficient time (ms) to fully charge the coil. The longer duration provided by most electronic points represents more current in the coil output at higher rpms.

This was possibly the most helpful and interesting thing I have ever read on the site.

I personally gap at 0.026 as per Bently, but Tim we could just compromise, 0.028 on cyl 1/3, 0.026 on cyl 2/4 :twisted: :P

Sun Dec 06, 2015 6:42 am

ashman40 wrote: Some topic discussions.....

Electronic ignitions (technically, electronic points) - provide a consistent ignition trigger as well as increased dwell. The increased dwell is where you might see a performance improvement. Dwell represents the "time" allowed for the ignition coil to "charge". This time is represented in degrees of rotation. The greater the number of degrees the more "time" available for the coil to charge. At idle, this time is not so critical since at lower rpms there is more than sufficient time to fully charge the coil. As the rpms go up, the angular time remains the same but the actual time (milliseconds) goes down. At higher rpms this could mean insufficient time (ms) to fully charge the coil. The longer duration provided by most electronic points represents more current in the coil output at higher rpms.

High voltage coils & Spark plug gaps - Higher voltages can jump larger spark plug gaps (higher resistance). For coils of less than 45KV you will find spark plug gaps below 0.030". Once you get above 45KV you can open to 0.035" or even as large as 0.045" in some cases. Larger spark plug gaps make for a more reliable ignition of the air-fuel mixture and necessary in higher compression engines (harder to ignite). Cylinder compression, air-fuel ratio and oil leaking into the combustion chamber all affect how easy it will be to ignite the air-fuel mixture. At higher rpms, the rated voltage of the coil may not mean as much because the reduced charge time (see dwell). So using mechanical points with a high voltage coil will result in performance decrease at higher rpms.

To summarize, a HV coil allows the use of larger plug gaps. To reliably fire these larger gap plugs at higher rpms you need more dwell time which can only come from electronic points or some type of dual-point ignition.

talljordan wrote: This was possibly the most helpful and interesting thing I have ever read on the site.

I second TJ on that. Ashman's explanations are consistently among the best on the site.

:idea: Ashman - you should compile a book of your posts! I'll buy it. :)

Sun Dec 06, 2015 8:13 am

ashman40 wrote:
To summarize, a HV coil allows the use of larger plug gaps. To reliably fire these larger gap plugs at higher rpms you need more dwell time which can only come from electronic points or some type of dual-point ignition.

The way modern designs have gotten around this problem is to use multiple coils.

The Ford EDIS-4 system for example uses two coils for four cylinders. Since each coil only fires two times per engine revolution instead of four, the rise time (dwell) for each coil is effectively doubled at any given RPM.

Sun Dec 06, 2015 9:00 am

Luft kühl wrote: The way modern designs have gotten around this problem is to use multiple coils.

The Ford EDIS-4 system for example uses two coils for four cylinders. Since each coil only fires two times per engine revolution instead of four, the rise time (dwell) for each coil is effectively doubled at any given RPM.
Excellent point. This is also why you see individual coil packs (one per spark plug) on many newer engines.

Sun Dec 06, 2015 12:41 pm

ashman40 wrote: Luft kühl wrote: The way modern designs have gotten around this problem is to use multiple coils.

The Ford EDIS-4 system for example uses two coils for four cylinders. Since each coil only fires two times per engine revolution instead of four, the rise time (dwell) for each coil is effectively doubled at any given RPM.
Excellent point. This is also why you see individual coil packs (one per spark plug) on many newer engines.

Would you need multiple distributors and/or multiple condensers as well?

Sun Dec 06, 2015 1:40 pm

No.

Modern ignition systems do not have points, condensers, or distributors.