I have read the archive posts on spark plug selction, AC43/AC44/AC45 and so on. My question is what are the effects of selecting a plug that is one or two heat ranges too hot, apart from short plug life. I have an LS4 and am currently running AC R44T and thinking about going to a AC 45T (or #5 heat range equivalant. I am looking at the plugs as a possible missfire culprit, back 4 cylinders wet and sooty!
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Re: Spark Plugs!
Plug life is a result of how many times it fires and the electrical energy causing errosion of the electrode, not heat range. Heat range is passive in that all it does is transfer tip heat to the cylinder head.
Using different heat ranges in different cylinders is not all that uncommon. I had a 318 Mopar with a cylinder that demanded a plug one heat range hotter. If I used the same heat range plug all around, that one cylinder would begin misfiring within a couple of minutes. Put a hotter plug in that cylinder and it would run fine forever. I theorized that it must have been a combination of that cylinder being the first cylinder at the water pump outlet being cooler and the mixture difference reaching that cylinder being a little fatter than the rest.
If I had this occur on more than one cylinder I would probably look for what is causing this. Your carb may be a little too rich or poor ignition performance on those misfiring cylinders which could just be coincidence that they are grouped. Hotter plugs may (or may not) only address the symptoms without solving the problem's source. -
Re: Spark Plugs!
The AC recommended "4" heat range for normal driving (AC 44)is too cold, and AC heat range "5" or equivalent is best for normal urban and freeway driving.
Since AC no longe offers non-resistor plugs in heat range "5" (This would be the old AC 45), my recommendation is to use the NGK B4 or Denso W14-U. These are both non-resistor types of approximately equal heat range to the no-longer-available AC 45, plus they have a more corrosion resistant shell coating.
I always used to use AC 45s for normal driving and AC 43s for race track hot lapping on my '63 L-76. AC 44s fouled out quickly on the street.
DukeComment
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Re: Spark Plugs!
Thanks for the replys. Are the NGK B4 or Denso W14-U tapered seat plugs. I have been looking at some cross reference charts and the best match I can find in the '5' range are either AC R45T / Denso T16R-U or AC 45TS / Denso T16P-U. I am still trying to find a comparative chart for NGK.Comment
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Re: Spark Plugs!
Found an NGK chart, AC R45T / NGK YR5 or YR5GP and AC45TS / NGK UR4 or UR4GP. Do you know which way the the numbers run in relation to heat range, not all makers run the same way. These charts are not real clear either as some makers appear to list replacement plugs that cover more than one heat range, eg, I have seen a maker recomending a plug that covers both the #4 and #5 heat range in AC. This is not getting any easier.Comment
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NGK smaller # = hotter.
NTComment
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What about 43XLS vs. R43 plugs...
...for a '66L36? Currently running the 43XLS plugs, only because that's what the car came with. The plugs are in fine shape and the car seems to run well with them. I have a set of NOS green-band R43's on the shelf. Will installing the R43's give better performance?Comment
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Re: What about 43XLS vs. R43 plugs...
the 43 XLS is an extended tip plug which will work better and last longer than the R-43 which is not a extended tip plug. the XLS is a 3/4" reach plug only for the early big blocks. the later big blocks used the taper seat plugs but i would still use the extended tip for longer plug life and use a 45 heat range because the fuel wash makes the plug act colder then a 45Comment
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Re: Spark Plugs!
Sorry, I was referring to early SB plugs without tapped seats. My AC spark plug catalog calls for the R44T for early seventies 454s. If you are experiencing fouling problems, try a set of R45T if they are available. The second digit in the AC designation - "5" is the heat range. The "4" means its a 14mm thread.
The higher the heat range number the hotter the plug. This applies to AC and most other manufacturers, but NGK is just the opposite - a hotter plug has a lower number.
I recommend NGK and Denso for early engines that originally had non-resistor plugs because they are the only current manufacturers that offer non resistor plugs in the proper geometry and heat range for early small blocks.
Since your engine originally had resistor plugs there's no reason to use NGK or Denso. Cross referencing can be tricky, so stick with AC since correct alternnative heat range plugs are available.
DukeComment
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Re: What about 43XLS vs. R43 plugs...
I agree with Clem that an extended tip plug (AC suffix "S") will provide more fouling protection and a wider thermal operating range than a standard tip plug.
There have been reports of interference with extended tip plugs with domed pistons. I've run them in my '63 L-76 without incident, and they should be okay for non-domed pistons, especially with post 1970 low compression.
DukeComment
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Before
attacking the plugs, you might want to spend a few $$$ and have the car put on an engine analyzer by a competent mechanic. With all plugs the same, I think I'd be questioning why only the back four cylinders are fouling out. This just might be a case of plug wires, valves, Etc.... Watching dynamic firing on the scope coupled with compression and leak-down test will give you much more complete picture of what's happening!Comment
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Re: Before
If the deposits are "wet" it could be an indication of excess oil slipping by the valve guides.
DukeComment
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Re: Spark Plugs!
Duke-
I am just curious but why are the 43's better for the track? I understand they are not as hot but why does that help there?
Sorry for another novice question...
Todd.Comment
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Re: Spark Plugs!
The higher the average horsepower an engine generates in actual operation, the more heat is transferred to the plug. Obviously, when hot lapping a track you are running the engine for sustained periods at high load and a normal heat range plug for the street will overheat, which can get the engine into preignition that can lead to destructive detonation. Thus, for the track you want a "cold" plug - one that transfers heat readily and will not overheat in sustained high output operation.
Conversely, too cold a plug will run too cold a tip temperature on the street to burn off deposits. As a minimum we want the plug tip to operate at about 750 degrees F to burn off deposits, so a "hot" plug is required for street driving where the engine rarely operates at high load for any length of time. Below this tip temperature the plug will rapidly foul with deposits.
At the high end we want to keep the plug tip below about 1650F to avoid preigintion, so a "cold" plug is necessary for road racing. The terms hot and cold refer primarily to the rate of heat transfer that the plug supports. A cold plug transfers heat rapidly to prevent it from overheating in sustained high output operation. A hot plug retains heat to prevent them from fouling in normal driving, which includes lots of idling and low load operation.
Many engines have been destroyed in racing because too hot a plug was used, and the engine got into preigntion and detonation. My usual rule of thumb for running a production engine on the track is two heat ranges colder than OEM, but in the case of the OEM AC 44s that were used on sixties SBs, they were already too cold for the street, so the 43 turned out to be just right for the track and the 45 just right for the street. Street plugs are fine for autocross (less than two minute course) and drag racing. BTW my '63 owner's manual has recommendations for "heavy duty high output operation", so when I started hot lapping my car I just used their recommendation for AC heat range "3". For "extreme high output" operation or some such euphamism, the owner's manual recommended heat range "2" but since I never ran the 12 hours of Sebring, heat range "3" was fine for my hot lap sessions.
When selecting plug heat range for a given application the first guess should always be conservative - on the cold side as the consequences of too hot a plug - preigntion and detonation are much more serious that the fouling that can result from too cold a plug.
DukeComment
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Re: Spark Plugs!
Thanks, Duke!! Very informative as always.
Todd.Comment
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