VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 28 plugs and points. Standard Gap or Increase?

Hi Guys,

I have heard the for and against arguments of increasing the plug and point gap to gain improved performance from later model coils. I run a coil from the 60's, points are standard setting, and as a trial have just increased plug gap from 25 to 30 thou. Would welcome thoughts and opinions from wiser heads than mine.

Regards

Ray

Hi Ray,

I don't know about the 4 cylinder models, but a noticable change can be made with the 6 by increasing the spark plug gap to 0.040 and advancing the timing from 12 to 18 degrees BTDC. Point gap stayed the same, between 0.018 and 0.022.
When I first got my 30, this was the first "improvement" I tried - and it WORKED!

Dan

Cheers Dan, thats a good strating point

Regards

Ray

I think that is a great topic and worthy of some experimentation.

Not enough of us have experimented with plug gaps in the 4 cylinder Chevys. Part of that is because there are many different plugs and heat ranges being used. We just had a discussion during the Tech Session on the first Mid-America Tour on spark plugs. Some are running long reach plugs with higher heat ranges without problems. Two reported that they lost performance with Autolite 3077 on long higher speed runs. Some felt that the Champion W89D or W-18 (older designation) were superior plugs. There are a bunch of posts on the internet recommending the 3077 plugs in tractor engines and stating that the Champions are junk.

I know of several that are running AC 78S (longer reach) plugs. Maybe some are running the original AC Z plugs (also longer reach). Then there are those running the short reach AC 75-78 plugs (increasing heat range with number but not long reach).

I would expect that increasing the gap on the short reach plugs would give better performance when combined with a modern high voltage coil. I would also expect that a larger gap on a long reach plug would make them too hot and reduced performance would result.

Anyone else want to experiment and report results? It sure would be nice to have a dyno to actually get documented and scientific results. As we all know the typical anecdotal testimonials are common but really inaccurate and worthless.

When I got the car, it had 3076's in it and even after I tidied up some issues, the plugs were always well carboned and the engine belched smoke. I switched to 3077's on a recommendation here and because they have a bit longer reach. The car at that time ran even better. Now with more tuning it runs like a champ. I am running a modern coil and could try a larger gap. At present i have them set at factory (don't make me look it up). I have no idea what the points are set at because i have not checked.

My 28 coach had Autolite TT10 plugs,(when I first got the car), which are a short reach (and an older number). The car was slow to start, but once going I thought it ran ok. After the the plugs fouled a couple times and caused more hard starting problems, I decided to put in the long reach plugs. I used the Autolite 3077 and compared where the plug points sat in the head with a 28 head I had sitting around. It now fires up right away and sounds more "crisp" at the tail pipe at a high idle. The low speed idle is much smoother as the old short reach plugs even when cleaned up still had a slight miss. With the 3077s no more miss at all! The 3077 plugs are at the heat range where the crud stays burned off. I haven't heard a peep of pinging out of the engine, but I also haven't driven it when it was hot out. I agree that a dyno would tell all we need to know but a good gas mileage run done properly would tell just as much. Just a note here but I had a similar problem with my 24 Olds 6 cyl with short reach plugs making it a nightmare to start and plugs fouling out. That car did lousy at the Newport Hillclimb the first year and barely made it up the hill at 107 seconds (second slowest car at the entire event in all classes), but the second year I had put in long reach plugs and it woke up from a dead sleep, flew up the hill and took third place in class at around 67 seconds if I remember right, but it was almost a 50% improvement in times. I felt like an idiot for 12 years looking for the problem on that car and it was the plugs all along. Who would think that nice NOS plugs would do that I was thinking. The shrouding of the plug points by the spark plug hole really does make the engine sluggish on both my cars.

I had AC 87's in my car when I bought it. I had overheating problems so I tried Autolite 3076. They just fouled up and ran poor. Last year I had a valve job, new head gasket, new wiring harness along with NOS AC 'B' plugs. The original plugs. What a difference!!! I'm not sure what new part corrected the problems but I'm very happy with the original plugs.

All your comments are well recieved and appreciated. I am currently running 3076's and have done so for the last few years. I do have a couple of sets of Champion W14's and if people feel they would run better I would like to hear. Basically my 28 runs ok, the 3076 carbon up slightly on the outer housing and the electrode housing is a nice light to mid brown. I have always up until yesterday run at 25 thou as per the standard specs, but am trying 30 thou.

My questions for wiser heads than mine is

1. Would I notice an improvement if I changed from the 3076 to the W14's, or should I throw them out and try something else?

2. Should I try 35 thou

3. Should I replace my 60's to 70's coil with a new 6V Coil.

As allways all suggestions and or comments are most welcomed.

Regards

Ray

Hi Chipper,

Have I read your comments right that the Champion W89D or W-18 (older designation)are the same plug, and not being available in Aus, can you suggest a dealer

Regards

Ray

For the Champion Champion W89D go to restockit.com, they are $62.52 for a box of 8 plugs.

The Autolite 3077 is a better buy and probably a better spark plug at $1.99 each from Advance Auto Parts or O'Reillys auto parts.
You may be able to order online from Advance or O'Reillys

Ray, if you have a vac tank and disconnect the fuel line to the gas tank you will have a nice test tank to use for a mileage test. I would start out on a nice flat secluded stretch of road and only run the test in the same direction. Mark a "starting line". Try different plugs at different gaps and have something to measure the gas in accuratly. Completly drain the gas from the test vac tank and run the car till the carb is empty. Then fill the test tank with the measured gas. Set your plugs and see how far the car goes down the road till it runs out of fuel and mark the place. Go back and repeat with different settings and drive the car as close as possible to the previous runs. If I can get the wiring finnished up in my coach I will try it myself, that is if my messed up knees will let me. One thing to remember is the gap settings are supposed to put the hottest spark in the cyl at a given compression ratio and is also factored by the type coil used. A hot spark at the right place (long reach vs short reach) will generate more power as the burn gets a better start. The gap will change the spark "flame" itself also. Give it a try and let us know what you find out. As far as getting plugs goes, some stationary hit and miss gas engine parts guys here in the states carry several types of plugs. One I can think of is Gas Engine Enerprises. I think they have a website also.

After reading earlier posts I replaced the AC77 short reach plugs that were put in the car in about 1946 with the autolite 3077 long reach plug with .035 gap. There was a huge differance in the way it started and ran. Much more power and runs smother too. I am using a 1954 coil and condenser thus the larger gap.
I have no clue if this is the best set up for the 1919 FB50 but it was a definate improvement.
I hope someone has the time and fortitude to make ten or fifteen two mile test runs with diffrent plugs and gaps. It would be interesting but probably not me. It would require some extra help moving and restarting an empty car that many times and changing plugs and gaps. I see several people having fun all weekend with this chore.
Hutch

I am going to try increasing the gap, but it won't be until next week some time. This weekend I need to attend my second wedding.

i was able to get to the car today and increased the gap from .025 to .035. Car fired up just fine. i took it out for very short run and it seemed to, according to the Butt Dyno, have a bit more pep. What i can tell you is the 3077 plugs were spotless and the ceramic was clean, with no black carbon build up.

I would have gone farther, but I had to help #1 son prep the race car and #2 son work on his exhaust on the RX-7. Yes, our fleet has grown.

i will do some more runs and report back.

Hi Shawng,

You cant beat the butt dyno, thanks for the feedback. I have a set of 3077 and W18's coming from the states next week and will do the same type testing.

Regards

Ray

Well I could have used the app on my iPhone, but where is the fun there? And i don't have a before to compare with.

Hi Guys,

THE GOOD NEWS IS

Changed from Autolite 3076 to 3077, the improvement was noticeable on start up. Engine runs smoother, more responsive, exhaust note is not as rough, and subject to further testing believe she pulls a bit better on hills. The other noticeable difference is that previously I had an engine miss if I idled when fully adavanced, now gone.

Then tried W18's and the miss came back, with the rougher exhaust note.

So at this stage I will stay with the 3077's and do further testing with a modern coil and try 30 and 35 thou.

THE BAD NEWS

Is it just a coincidence, but on two of the 5 test runs I did, developed a significant miss near the top of a medium climb. Pulled up, took off again no problems. Checked plug leads, no problem, checked fuel line to carby, no problems. Fine on the flat. If I did not know any better I would say if was starvation from the vac tank, but don't think so.
Would the 3077's be pulling more from the old coil (60's vintage)Than it can handle.

Any thoughts from wiser heads then mine?

Cheers

Ray

Good to see things are working out. In my opinion, a 60's coil is still modern compared to the original. As to pulling more, this is not how it works. Spark plugs don't put any load on a coil as they are an open circuit as compared to say a light bulb circuit. However as the gap increases, it takes a higher voltage to jump the gap, so a weak coil will have a tougher time. As well, the voltage required to jump the gap increases as pressure in the cylinders increases. This is why modern cars with high compression need higher voltage coils. But regardless of all conditions at the plug, the current the coil pulls form your electrical system is constant and a function of the windings in the coil. That all said, a weak or aging coil will have a harder time generating a good solid high voltage and as the coil heats up physically, it gets worse. Coils do wear out due to the extreme conditions we force them to work under. Any electrical stuff does not appreciate heat.

Thanks for the advice, and as an after thought I checked the points. They were a few thou under, reset at 20 thou, which I believe is standard. Will road test in the morning. If no luck will look at timing and fuel.

19281sgreat, I have no stake in the reputation of Champion spark plugs but do not think your comparisons are a fair to Champion or even Autolite, they are not an apples to apples comparison.
Champion never cataloged the W14 or W18 plugs for your Chevy, through the years they did catalog C4, C16C, W18Y, W89D all protruding nose plugs.
Autolite currently have a website with pictures of their plugs the 3076 is a standard plug comparable to the W14 Champion ( W18 is the same but hotter) and the 3077 is a protruding nose plug similar to a W89D or W18Y.

One item I did want to add to the above. I am presuming AC was the original equipment plug on the 1928 and they cataloged the number 78S long reach plug for that year. For 1924-7 they cataloged the 78 Standard reach.

The earliest Chevrolets used several plugs some AC CICO and AC Titan. They generally were long reach plugs with extended electrodes.

Of interest to this discussion the 1926-27 (Series K, V, AA) are listed as originally using an AC B plug.

The 1928 engines used an AC Z plug. It is an extended electrode plug.

The AC 78-S was a later replacement for the AC Z which was later replaced by the AC 76.

The AC 78 was a later replacement for the AC B and also later replaced by the AC 76.

The Autolite 3077, Champion W89D and W18Y are modern extended electrode plugs that many have found to perform better in the '28 engines. Some find they are okay in the '27s but others find high speed or hot weather missing with those "hot" plugs. In that case the W18 or Autolite 3076 or equivalent plug might be a better replacement.

Ok guys, here we are, round 17 man versus machine.

The story so far is

1. Wanting to improve the performance of my 28, I purchased a set of 3077 and W18 plugs to test.

2. In my spares box I have 2 sets of 3076 that I have had for a while, but then discovered the plugs in the car are actually W14, which is the equivalent anyway.

3. The bottom line is for the last 20 years plus I have been running W14's, and embarrassed to say did not know any better. Have done 700 mile rally etc, with no problems.

4. Fitted the 3077, engine runs fine on idle, better exhaust note, more responsive on the road, and seems to pull a bit better up most hills (note the most hills comment)

5. During my test runs, developed a short miss within half a mile of the same spot on each run, I then pull up, engine a bit rough for 1 to 2 seconds, then runs fine, and I return home.I should point out that at the spot where the miss was occurring, the engine was not under as heavy a load as it had been earlier in the run.

6. Thinking this must be a fuel starvation problem, I removed both the in line filter and one way valve fitted just before the vac tank, with the next step planned was to pull the top of the vac tank.

7. Removing in line filter and one way valve makes no difference, miss still there, on same location around medium climb road.

8. Just prior to accepting its a fuel problem, refit the W14's and guess what, no miss.

9. Fit W18's and engine runs worse.

10. Refit 3077, miss returns.

11. Try retarding engine when miss started, and miss got worse.

12. Increased gap on 3077 to 35 thou, miss occurred earlier, and engine ran rough on fully advanced

13. Fit W18's with increased gap of 35 thou, miss occurred earlier, and engine ran rough on fully advanced

14. Refitted W14's with normal gap of 30 thou and engine runs fine, no miss, but not as much power as with 3077's

15. Reconect in line filter and one way valve, engine runs fine

16. Have eliminated fuel as a cause, and am now thinking either coil, condenser or timing. But who knows??

17. HAVING FELT AND HEARD THE IMPROVED PERFORMANCE FROM THE 3077's I WANT THIS ALL THE TIME.

Any suggestions most welcome.

Regards

Ray

First suggestion, have a cold beer! And while you sit and relax, we can churn over the data and postulate. I commend you for doing such an awesome amount of research.

When you increase the point gap, try advancing the timing a few degrees as well and see what happens.

You don't say what coil you are using. Are you running a stock coil or a more modern one. If you are not running a modern I suggest you install a 1954 6-volt coil along with the 1954 condenser.

Why 1954? What is special about that year? will any modern 6V coil work? Inquiring minds need to know.

Try to make things simple to the parts kid. If you specify a 1954 you will get the latest 6-volt coil and it is designed for a 6-volt system as you have. Same for the condenser. Ask for anything else and it is a crap shoot as to what will be laid up on the counter. Don't confuse them with too much information.

perfect sense, been there done that.

Right, if the 54 is available do it! makes for a much simpler transaction. If they aren't available at the chain auto parts store find a Mom & Pop Auto Parts and farm store down in the old part of town.

Gentlemen,

ARE THERE ANY CHEV WHISPERERS OUT THERE ?????

The saga continues, and I would like to thank everyone for their suggestions and comments so far, in particular an aussie chev man, CJP'S 29, who is holding my hand through this very frustrating "event".

Today's developments are:

1. Replaced the coil with a modern 6V unit, making sure it was suitable for a non ballast resistor ignition system.

2. With the W14's fitted went for a run, engine ran fine,no miss, but lacked the power increase and response of the 3077.

3. Fitted the 3077's, engine developed miss again in the same location, approx, but in all other parts of the run, was fine, more power, ran smoother, pulled very well on hills.

4. Replaced the condensor, did one circuit, no miss, thought I had solved the problem, then another lap, miss returned.

I should point out again to all the miss is in a spot during the run when the engine is not under the greatest load, and the series of events are, engine looses power, audible miss and vibration, pull over, engine runs rough for 1 maybe 2 seconds the full power again regardless of train or speed.

If it was not for the fact that their is no problem with the W14's I would be looking at fuel.

At all other times the engine is without doubt running better on the 3077's, otherwise I would say it's too hard and stick with the W14's or 3076's

I have no idea why my engine appears to not like 3077's.

I have changed back to the W14's and will do as many runs as I can after work tomorrow.

Any Suggestions??????

Regards

Ray

For a "suggestion"
Try the standard gap on the 3077 plugs but install a second washer to pull it back a bit from the combustion chamber.

I get a feeling that the 3077s may be a bit hot for your engine. After pulling a grade (heats the cylinders) you are getting pre-ignition from the hot plug electrodes. Once the plugs cool a bit they work as they should. An extra gasket might help. AC 78S plugs (out of production) could be a better fit for your engine. Another possibility is to use adapters and modern plugs. There are a bunch of modern longer reach plugs with various heat ranges.

I had the same thought about the temp of the plugs as Chipper just said. One thing you didn't mention is the outside temperatures while during the runs.

Of course I didn't think to ask about the fuel being used. Is is straight gasoline or have ethanol or other stuff added? I said stuff to be nice and since this is a family oriented site.

I do have one other “suggestion” and that is to try the actual spark plug that Champion catalog for your car the W16Y (2001 catalog).
The W14 Champion (3076 Autolite) works but may be too cold.
The 3077 Autolite (W89D Champion) appears to be too hot
The W18 has a longer reach and should not be considered
Moving to the W16Y will give you a slightly hotter plug than the W14 but with the projected core nose of the 3077 Autolite
The W16Y are easily available as they are sold as a modern day replacement for the 3X Champion on the Model A and sold by F**d vendors as Snyders ( $7 US)

Hi Guys,

I do appreciate the replies, and thank all for taking the time to make a posting.

GOOD NEWS AT LAST, as I may have finally broken through, and come up with a possible cause of the miss with 3077's.

I don’t know what I have worn out more in the last 3 days, either the threads on the head from 1 Million plug changes, or the 7 kilometer test track I have been using.

I have done 100 miles in the last week and a bit, but have not been more than 5 kilometers from home.

The latest and most fruitfull developments are as follows:

I did 2 runs with the W14’s. No miss, no problem, but definitely not the same smoothness and response of the 3077’s

Then I did 1 run with the W18’s. No miss. No noticeable power increase, but engine a bit rough on fully advanced.

Then did 1 run with W20’s. No miss. Power seemed a bit better than the W14’s. But again engine a bit rough on fully advanced

Then the penny dropped. TIMING.

My Chev has never seen a timing light. I have allways tuned by ear, and with W14’s fitted.

So I did 2 runs with the 3077’s fully retarded, driving it very hard, pulling up hills at 20 mph etc, no miss

Did 1 run, fully advanced, exact same miss, exact same spot, pulled up, rough idle for 1 to 2 seconds then fine again all the way home.

Just to confirm, did another run fully retarded, no miss.

I SHOULD MENTION THAT THE ENGINE SEEMS TO RUN BETTER, SMOOTHER, AND MORE RESPONSIVE WITH THE 3077, THAN WITH ANY OTHER PLUG TRIED SO FAR. OUSIDE TEMP DURING ALL RUNS WAS BETWEEN 10 to 20 DEGREES CELCIUS.

Interesting observation was that there was not the noticeable power difference (with the 3077's) at road speed when changing to fully advanced as with the W14’s, or the roughness when changing to fully advanced with the W18’s or 20’s.

Again I welcome any comments as to wether you think its timing or pre ignition.

Regards

Ray

What this all illustrates is how critical is the ignition of the flame in the cylinders. What most people don't understand is that the gas/air mixture is ignited at the spark plug and then travels at some speed across the cylinder. If the flame proceeds too fast the maximum pressure is created too soon and power is reduced (if fast enough then "spark knock" occurs). If too slow then the maximum is too late and power also lost.

It should be deduced from the above that the timing, intensity and strength of the ignition spark is critical. But also the ratio of vaporized gas to air [1:14 is stociometric (ideal)], total amount and temperature of the mixture are factors.

I think that Ray's experiments illustrate that small differences in ignition intensity and timing can have a noticeable effect on the performance. Normally these factors are not noticed without using a dynomometer in a laboratory and strictly controlled conditions.

What may not be understood is that changes in carburetion, flow pattern in the intake system and fuel used can also effect performance. It would be interesting to know what the effect of adding 10-15% diesel to the gas would do. Also the difference in regular gas with ethanol, without and premium gas. All those gasoline mixtures will have a slightly different burn rate. May or may not make a noticeable difference. The scientist inside me wants to know. Ray, I fully understand that there is a limit to the time, desire and dedication needed to run the experiments. Just would be interesting to know the effects.

Going by memory here, so the numbers might be off. If you run full retard, then at idle, it is 0deg. and at full speed, about 22 deg due to the auto/mechanical advance in the 28 distributor. At full advance, this moves to 22 or so at idle and about 45 at full speed. This gets tricky, since you can't go below zero as the starting point. As I see it the only way to limit the top end is to fabricate some sort of a stop on the manual advance. this all done once timing is determined to be correct. Another observation is that since you did not overheat with no initial advance, perhaps this is what's off and a simple adjustment is all that is required.

Shawn and Chipper,

Thanks for your comments. The easy way out, but I suspect not the right way would be either just drive it retarded, or adjust the advance retard bracket so that the current dist position at retarded now becomes fully advanced. But as Chipper says, the scientist in us wants to know what's going on. I know how to time a modern engine with a timing light, so if there is a way to use the same on a 28, can you please advise things like where is the timing mark on the pulley, and what is the static reference point to measure buy.

I am now starting to feel better as the muddy water is starting to clear.

Regards

Ray

I would prefer you drive sensibly and not retarded.

very clever, never thought of that.

Beginning with the late '27 engine, there are two timing marks on the flywheel and a window with indicator in the clutch housing. They can be timed with a modern timing light as long as the last person put the flywheel on the crank in the correct position (it is possible to put in in six different positions)[ask me how I know][It will be corrected soon]. With full retard the UIC mark should be on the indicator. UIC is for upper center with the actual line between the two letters. Modern term is TDC or top dead center. Full advance should be at the 25 mark on the flywheel. That is 25 degrees before TDC or UIC. According to the "book" the mechanical advance begins to function at 22 mph and full advance is 40 deg.

Of course that suggests another possibility. If the springs and weights do not operate properly then the mechanical advance could occur at too low rpm. Sticking advance mechanism would render too much advance at low speed and loss of power/poor idle etc.

Have fun and let us know occasionally what you find.

Thanks Chipper,

I will check tonight but suspect I also removed the flywheel several times over the years and cant recall being too dillegent about mounting back in the same spot.

Cheers

Ray

I just went out to the garage to take a look at the timing mark. I found the pin in flywheel housing, but in order to see it, my face has to be an inch from the exhaust manifold. Or I use a mirror.

Just connecting the dots with this post.

A followup from Ray: Spark Plug Update

Cheers, Dean

Hi Dean,

Pleased to say that 7 years on and the 3077's are still running fine.

I am also still adding a litre of diesel per tank of gas to a/ lower the temp in the combustion chamber due to the long reach plug and B/Its a very economical upper cylinder lubricant.

I reflect on the days when I had to clean the W14's every few hundred miles, versus the 3077's being never.

Cheers

Ray

Hey Ray,

Glad to hear your update about the 3077 plugs.

Also, cool tip about using diesel fuel as a cooling and lubricating additive.

Cheers, Dean

Hope you guys don’t mind me adding this and also asking a question but it’s directly related to plugs. When I received a customers 31’ Chevy car for restoration, he also asked me to evaluate how it ran saying that it had been tuned up but I don’t think he was happy with the way it was running. While it did run decent, I found that whoever did the tuneup, gapped the plugs at .028 which I believe is original spec or close to it. The timing had been advanced some but not to the 18btc. The car ran ok but idled roughly and power was only fair. Gapped the plugs to .040 and it was like a new car. I realize many here know this already but JUST the gap change made all the difference. Now my question is this. Seeing since we’ve learned to advance the timing and increase the gap with our somewhat better gasoline, will I need to do the same with my 32’ Olds flat head 6? I will be running the original AC G-9 plugs and started to think doing the same improvement on the plug gap as we do on our chevys, would be worth a try. A fellow 32’ Olds owner who’s finishing up his coupe and hasn’t run it as of yet, was unaware of the Chevy “fix” and wasn’t sure if it would be needed. There are other guys running their Olds to spec but none I’ve spoken with have even tried experimenting. Thoughts?

You will never know until you try it.

That's exactly what I'm thinking. What could it hurt if I monitor the test closely.