Anyone can chime in on this. I pulled the plugs out that were installed by Total Performance last Fall, which have only a few hundred miles on them, and here is what I see:

They are Autolite 66's. The reach is the same as the NGKs but the electode extends only 5 mm as opposed to the 10mm the electrode extends on the NGK zfr5n. The old plugs are very black on the electrode, with no signs of metal flakes, which means pre-ignition was not occuring to any destructive dgree. The thing that bothers me was that the gap on the old plugs was set at .020". Does this make any sense at all. The electrode does not look overheated. It has the stock cross section and mass, and is not thinned out at all. In other words, it does not look as if excess heat would have distorted this out of adjustment. Is there any reason the speed shop would have narrowed the gap down to .020? I have installed the new ones with a gap of .040". Does this sound reasonable? Which gap is most resistant to missfire;l arger than stock, or smaller than stock?

I did not mill the head other than to true it up. Could the piston have closed the gap up? It does not seem at all likely, but it makes me wonder if the extended tip plug is completely free of interferance concerns with the piston. I appreciate any elaboration you might wish to extend on this subject. I will not try to start the car until I have heard back on this topic. Thanks much.

Sam

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I wouldn't be afraid to run it with the new plugs at .040. The plugs do not reach down far enough to hit the pistons. The valves would hit first anyway.
Sounds like the shop may have gapped them that way on purpose, maybe a poor spark or if your electronics were bad, (causing low spark output).

Dan is the man, he might have a logical idea........and some words of wisdom!

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Is the tighter plug gap to keep the turbo from blowing out the spark flame?
Does this work, and should I close my gap down to maybe 30? I was always told you get a hoter spark with a bigger gap. I don;t think the ignition is weak. It is an MSD6 box and a new coil.
Sam

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Aren't both valves fully closed by the time the spark fires across the plug?
If so, the turbo would not blow out the spark.

-Mac

I can't think of any benefits to a plug gap of 0.020". Miniature plug gaps are, as you already know, used in cases of weak ignition systems. I think your plan to try 0.040" (or maybe even 0.045") is a good one. Are you running the NAPA Echlin long-tip rotor # MO-3000? If not, that'd be a good idea. I don't think the pistons closed up your plug gap, but I'm curious: Who gapped the plugs you just removed?

(you left off the metal ring washers on the new plugs...right?)

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I do not have the long tip rotor in, but I will get one. A guy named Jason gapped the plugs, or maybe he didn't and just installed them out of the box. They varied a bit from 020 to 025. I removed the ring washers. Which brings me to another question: what kind of torque do you put on a plug with no compressable gasket? Thanks man.
Sam

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Blowing out the spark is a figure of speach......

With turbo and super charged motors there's more pressure in the combustion chamber before the spark plug is sparked.

The higher the pressure the more voltage it takes to jump the gap. Also the larger the gap the more voltage it takes to jump the gap. Put the two together and eventually there might not be enough voltage to jump the gap, and you get a misfire.

The smaller plug gap is to compensate for the higher pressures so you won't get a misfire.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Thanks Emsvitil. That was a perfectly clear explanation. I think I will start with .040 just to get the NA part of the map tuned, and then maybe close down the gap as I start power tuning. The black on the plug is a jet black, fine poweder. Is it correct to assume that this means rich? Eli thought the entire fuel map was too rich, and it seems as if the plugs would support that.

I have read about plug reading, but the writers are always assuming one power run, and then a read. Can you learn the same things from reading the plugs after 200 miles of mixed driving? Mostly the car was used in cruise and tune mode, just trying to touch all the cells in the NA section of the map. I always apprectiate any and all advice here.

Sam

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All true, but if those factors combine to exceed the capabilities of the ignition system unless the plug gap is ridiculously small, then the ignition system's inadequate.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

If you got a good ignition it will prouduce a spark at any preasure. One must look at combustion ratios . Ie Fuel to Air. Lou Madsen taught me this . He Is My Hero A Professor at Virgina Tech.










Im Proud To Be A Hokie From Gagie

Hey Ron. Tell us more of what the good Doc told you. What do you look at, and what do you adjust in response to what you see? Thanks.
Sam

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On my race engine I look at two things plug tip and the Pyromter that i run down the Strip. I look at what my exhust gas temp is at the end of the run. Then I can jet my car or leave it alone to what I want to run. I know where I want to be.

Sorry,
I guess I was thinking of an oil burner in a furnace, where blowing out the spark is a real problem with improper gap.

-Mac

So Ron, tell us more about the specifics of what you are looking for, and how you adjust jetting based on what you see or do not see. Give us some cause and effect stuff here, and parameters for exhaust heat, and plug color.

Still on topic here, it seems as if the smaller gap would promote a rich misfire, if the misfire is caused by the moisture bridging the gap and thus grounding it out. Maybe this narrow gap has been a major part of the problems I was experiencing. If the engine was too rich, and if it was shorting this gap and thus misfiring, and if the O2 sensor was then giving me the resultant erroneous low voltage misread of lean, then I would richen things up. I was tuning into a sort of dysfunctinal death spiral for the engine. I never got to power tuning. I was only tuning for drivability, and when it would stumble and back fire, and then read lean on the O2 sensor, I would richen it up. And of course it got worse and worse. It got to where it would not run at all around 170 degrees ECT. Let's hope I am on the way to a fix.

I only have one more thing to do before I try to fire it up, which is run a heavy ground cable to the engine block from the battery in the trunk, and I started that project last night. . Keep your fingers crossed.

Sam

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One most remember this is a race engine built for a drag strip. The fuel is defferent I have run 93 octane fuel and my engine is about 11 to 1 compression. But my car preforms best on Sonoco 110 octane leaded racing fuel. But I can tell you what I look for. Insulator color slight brown and exaust gas temp at the end of the 1/4 mile 1250 degrees F. This is a true ram air engine and has to be jeted different than a street engine. I am only concerned about two issues idle and wide open throtle. Impractial for a street engine. I gap my plugs on 40 thousand and have not had any igintions issues with the Chrysler electronic igintion. I have a new MSd 6al that I boubht 2 years ago and have not used it. Going to put it on in the next couple weeks and see if any thing happens. I expect not.Thanks Ron Parker


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