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9/17/13 7:30pm - Original Message: 'The 'same' plugs are not the same'
BigShoes16
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Worcester, MA - USA

Vette(s):
75 L-82 Coupe 4-spd

Joined: 2/25/2013
Posts: 52
This past weekend I changed the plugs in my 75 L82.  For anyone who's done it you know how much fun it can be on a car with AC.

The car ran rough for the first few minutes and I chalked it up to warming-up, new wires and plugs, previous wires were worn and ripped... you know - excuses.  Well after it warmed up the "running rough" turned to outright misfiring.  Bad! Take-offs were horrible, sputtering, lack of power, so I brought the car home, put it back up on the ramps and waited for the motor to cool.  I took the plugs out of the driver's side and here they are below.  

Notice anything? They're all labeled "AC Delco R44TX" but they are not the same.  These were ordered together from a major corvette supplier (one that's listed to the left of this very window).  The 2 on the left are different from each other and both are different from the 2 on the right.

I didn't notice the difference when installing them because I opened and installed them 1 at a time, running and connecting the wire to the cap, then doing the next.  I never had them all together until I took them out tonight for inspection.

What I also found was that the second one from the left, with the green stripes on the insulator which was in my #1 cylinder, had been hit by the piston and the ground tip was pushed against the electrode.  At least I think it was hit by the piston.  I sure hate to think that I overlooked such a flaw when I installed it. (I have since re-gaped it but I think the electrode is too burned)

I don't want to put these back in, so I'm curious, how much damage could that have done and what everyone else uses for their small block mid-70's?





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9/18/13 12:14pm - Reply: 'Re: The 'same' plugs are not the same'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19457
You shouldn't need the TX plugs to begin with. The "X" is for "extended Tip".
If those all came in the same same package/box, take them back and demand a complete, matching set.
I doubt very seriously that the electrode was tapped by a piston...unless you have changed the stock pistons for domed 12.1  compression pistons. LOL You prolly just missed it. Looks to me like you got someone's returned plugs, or the store had several loose plugs, and just put them all in one box to sell to some unsuspecting soul. Tag....you're IT. Angry


|UPDATED|9/18/2013 10:14:50 AM (AZT)|/UPDATED|


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Joel Adams
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9/17/13 11:01pm - Reply: 'Re: The 'same' plugs are not the same'
F4Gary Gold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 869
Why didn't you just go to an Autozone/O'reilly/etc and buy plugs instead of ordering them from Mid America.

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9/18/13 12:50am - Reply: 'Re: The 'same' plugs are not the same'
BigShoes16
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Worcester, MA - USA

Vette(s):
75 L-82 Coupe 4-spd

Joined: 2/25/2013
Posts: 52
Thanks for the info. The TX is what comes up as spec for the '75, so I went with the catalog recommendation for my stock motor. All came in individually wrapped boxes and were added to get me to the free-shipping mark. So much for the $ I saved. Heading to the local parts store tomorrow for replacements. What plugs would you recommend for a weekend driver? Appreciate the help.

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9/18/13 7:58am - Reply: 'Re: The 'same' plugs are not the same'
Gunslinger
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Frederick, MD - USA

Vette(s):
1969 convertible L71 427/435 4-speed black interior

Joined: 9/8/2003
Posts: 3398
Any brand spark plug that is equivalent to original equipment should be fine for you.  In a non-modified engine, there's no reason to go to exotic spark plugs...they just serve to lighten your wallet.  I know people have their own favorites...AC, Champions, etc.  Back in the day when I worked at an auto center we sold the house brand and Champions...the house brand was made by Prestolite.  I used them and found absolutely no difference in performance.

All that being said...the speed shop I've dealt with swears by NGK and that's all they'll install.  


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9/18/13 10:47am - Reply: 'Re: The 'same' plugs are not the same'
F4Gary Gold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.

Joined: 8/26/2006
Posts: 869
I think NGK makes AC sparkplugs these days.  I could be wrong.

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9/18/13 12:12pm - Reply: 'Re: The 'same' plugs are not the same'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19457
Ya...the specs call for the R44TX....I wuz just saying ya really don't NEED the extended tip plugs. Wink They're fine, tho.
I think if you get a set that matches, you'll at least have a good starting point, if you need further diagnosis.
If your engine burns a little oil, you can go to a hotter plug, and that will help to keep from fouling the plugs. I have also found that the NGK plugs work well in GM engines, but don't know if the extra cost is really worth it.
The AC plugs available now are NOT as good of a quality(imho) as the older ones. The ceramic seems to crack easier, and I've taken some out of the boxes that the ceramic around the center electrode is loose, and will fall down and cover the electrode completely when installed.  The second from left plug in the pic above is indicative of the older style plugs...with the larger green stripes around the ceramic, and the beefier steel seat end...those are the good ones, IF you can find them anywhere....


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Joel Adams
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             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"
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9/18/13 1:39pm - Reply: 'Re: The 'same' plugs are not the same'
kstyer Lifetime Member
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CUYAHOGA FALLS, OH - USA

Vette(s):
1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Joined: 12/2/2003
Posts: 6410
Indeed, not all plugs are equal by listings.
 
Every brand of spark plug will have a plug to meet a spec.  Length, reach, tip extenction, heat range, seat, etc.   And these things do usually match.  But there is a HUGE difference that you will not see listed in any spec sheet or application chart.
 
The internal resistance of the plug varies a great deal.  
 
All manufactures match the plug resistance to their secondary ignition system.  American companies tend to get most of their resistance in the plug.  Europeans (Bosch) get most of their resistance in the secondary system, not the plug.  Asian cars are inbetween the two.
 
If you put high resistance plugs with a high resistance system, the tip arc temperature goes way up.  This does not mean heat range, that's different.  Heat range is probably okay.
With a hot tip temp, the plug electrodes burn away quickly, and create a very hot, yet very short spark duration.   If you put low resistance plugs in with a low resistance secondary spark duration is longer, but the arc tip temp may be too low to properly light the fuel.  This can lead to hesitations and fouling, including hard start and rough idle.
 
Typically A/C is GM vehicles.  Autolight and Motorcraft is Ford.  Champion is OE for Chrysler.  Bosch is most European cars, but there are some notable exceptions.  NGK and Nippondenzo are Asian cars.
 
This does not mean some mix and match can't be done to create positive conditions, and some  such as NGK work in our cars.  BUT the wrong combination can create severe negatives.  So how do you know?  Talk to someone who has done it on a particular car, or experiment and see what you get.
 
Hope no one is shocked by this.  LOL.


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