Correct Spark Plug 66 Vette 427
The Book Says I Should Use C43n Spark Plugs. For Some Reason People Tell Me To Use A 44 Spark Plug, One Size Hotter They Say. My Engine Was Rebuilt 12 Years Ago. Does Anyone Know The Theory Or The Right Spark Plug I Should Use? Thanks Dutch
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Re: Correct Spark Plug 66 Vette 427
Use 45N or 45XLS -
Re: Correct Spark Plug 66 Vette 427
If you run a hotter spark plug it should give you a little more hp because it tends to burn cleaner. It DOES NOT mean the water temperature will be running hotter/ higher. The theory is that it the insulating porcelin, will be shorter in length as you go higher in the heat range. The hotter the plug temp the shorter the length of the plug. Also, one of the other issues is the the heat generated from the spark plug hoter or colder has the chance to disapate into the head. In which could create a detenation effect. You do not want that!! In a nut shell, the 43's that originally was recommended would be fine and so would a 44, 45, and possible 46.Comment
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Re: Correct Spark Plug 66 Vette 427
The original GM recommended spark plug for your 427 is a 43N. (not C43N) If your engine is healthy and running properly, the 43N's will work.
If you experience some fouling, you may have to move up to a 44N but with todays unleaded fuel, spark plugs stay much cleaner so the 43N's would be my first choice.
Going to a hotter spark plug heat range "just because", is NOT a good idea. There are definite negatives involved. That's why engineering spent all that time selecting the COLDEST spark plug that would function properly. If all there was to it was "toss a set of hot plugs in it", those guys wasted a lot of GM's time and money.
If a big block fouls 44N's, there something wrong with it.Comment
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Re: Correct Spark Plug 66 Vette 427
Harry:
The spark plug specs for the big block engines were 43N but this was predicated on the fact that the big block Corvette was to be used in a manner that was consistent with the intended use-hard driving (racing?). The way most of us use our Corvettes is for going for ice cream or cruising the boulevard. Most of us would foul a 3 heat range plug in 5 miles! Most would agree that a 4 or 5 heat range is better. This does not mean that the spark is hotter but rather the plug will retain its heat a little longer to help burn off deposits and prevent fouling because the insulator inside the porcelain is shorter. The physical characteristics of the 44N or 45N are identical to the 43N.. A too hot heat range will cause "pinging" (pre-ignition). A 44XLS would also be fine since this is a fully threaded, extended tip plug which is effectively a 4 1/2 heat range. The 45XLS might be getting too hot since this is really a 5 1/2 heat range but others who have the experience might know better than me about this. If you are having fouling problems you can't be hurt by a 45N or 45XL (or R45N or R45XL) plug.
JeffComment
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Re: Correct Spark Plug 66 Vette 427
I disagree. You CAN be hurt using plugs that are too hot for the environment that it's in.
If it was that simple, the engineers would have just recommended 46's for all cars!
The 43N is a medium heat range plug. It's NOT a racing plug. It did foul years ago with leaded fuel but if a 43 or 44 can't survive, you have other problems that you are trying to cover up with higher heat range plugs.
I've had a set of 43N's in my 66 425 HP car for several years and I drive it a LOT. We go to the local car shows at least once a week and I can't even remember the last time I got on it hard.
Hotter is not the whole answer. Just hot enough is. If a plug heat range is too hot, the process of blasting off carbon during medium/hard acceleration doesn't occur. Instead, these deposits melt ON to the electrode.
Installing hotter plugs to eliminate an oil or fuel foul problem is like turning up the radio to eliminate the sound of a rod knock.
There are several more valid reasons why 45N's were never recommended by the mfg. for a big block Corvette, especially with todays unleaded fuel.Comment
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Re: Correct Spark Plug 66 Vette 427
At the risk of expanding this thread, are there any problems associated with using resistor type plugs (R43N)? A while ago someone suggested that they could harm original coils.Comment
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Re: Correct Spark Plug 66 Vette 427
Ask the guy who owns a big block and DOES run it hard on a regular basis. 43N is fine for the cruise in crowd, BUT will onlly last 2 times down the drag strip before breaking up at high rpm. Even the Chevy power book only recommends 43's for circle track racing & 44's for drag racing. For the street 45's work best for both low speed operation & high speed operation, in other words a good compromise plug for the street. Spend the money on 3 sets & find out for yourself what's best for your engine & forget the forum advice. An R plug will not hurt a good coil but will make it work harder. An R plug might finish off a marginal coil due to the increased resistance. Avoid R plugs, if you can.Comment
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Re: Correct Spark Plug 66 Vette 427
extended tip plugs see the "fuel wash" which cools the plug tip. when BBC were new their "ring package" was not very good,600 miles to a quart, was the cause of plug problems. if your engine is fresh with a modern ring package and the proper valve stems seals plug fouling should not be a problem but i would still run a extended tip plug. if you do not have the TI system i would run a extended tip plug in the 45 heat range. any time you do around town driving do not go to full throttle right away as this "bakes" the deposits on the plugs so take it up in RPMs at part throttle to the red line to clean off the plugs.Comment
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