Question: Spark plugs

[paul robb]

I know when the 1966 corvettes came out they come with ac 44 spark plugs. That being said, now that the ac 44 are no longer being made.
what are the ac plugs of choice ? any thoughts on this would be greatly appreciated....

 

[Red Vette]

You might check with a GM dealer parts department; they may have the recommended plug. You could also try the GM Parts House for their recommendations. Finally, check with C4C5specialist on this forum, I am sure he can get you the info.
Barrett

 

[Vettehead Mikey]

The 45s are one heat range hotter but work just great and are available everywhere.

 

[Hib Halverson]

If the recommended heat range was 44 and OE heat range recommendations were always conservative to avoid any complaints of pre-delivery fouling....how the hell will the 45, a plug one range hotter, "work great"? Perhaps "Vettehead Mikey"s definition of "works great" is different than mine.

In any event, unless the 66 in question is a show car and only gets backed in and out of a trailer or is driven such that the engine never warms up, I would not use 45s.

While the AC 44 might be discontinued, you can get 43s from Rockauto.com. I just checked

The 43 is the spark plug I'd recommend for a 66 327 which is driven normally. It's a really good heat range for the high-performance street driving duty cycle.

If your local ACDelco dealer doesn't have 43s. order them from Rockauto. I buy a lot of parts from them and find the their internet catalog easy to use, the ordering process is simple and they fill and ship the orders quickly.

 

[Vettehead Mikey]

Dunno Hib but the 43s were in the car when delivered and many owners went to the 44s to avoid fouling during average street driving. The same thing holds true today.

The 44s are hard/impossible to find so many people have tried the 45s and found that they work great. I've used them for decades with no problems.

 

[Hib Halverson]

Dunno Hib but the 43s were in the car when delivered and many owners went to the 44s to avoid fouling during average street driving. The same thing holds true today.

The 44s are hard/impossible to find so many people have tried the 45s and found that they work great. I've used them for decades with no problems.

I guess I'm confused. The OP said the OE plug was a 44 but you're saying it's a 43. I don't have my ACDelco catalogs available today so I'll just have to find out the answer later on.

If the OE plugs fouled during "average" street driving, either the driving wasn't really "average", the engines were running rich at idle or the engines had faulty ignition systems.

Back in the day, I had big-blocks and small-blocks in street high-performance duty cycles and with properly adjusted carbs and timing, I never ran a plug that hot. Back then, I ran the NGK 6 heat range which was close to the AC 42 and 43 ranges.

You may have used a 45 for decades but, in an engine that's driven in a sporting manner, a 45 is towards the hot end of the heat range scale. Unless the engine never warms up or is way rich at idle, you want to be at the other end of the scale for best performance.

The problem with hot plugs is that once you begin to load the engine, their tips start to run hot and that makes the engine more prone to detonation and, in extreme cases, pre-ignition.

For high-performance street use I submit that you always want use the coldest plug you can get away with, not the hottest.

Currently, I use the Denso 20 heat range in everything except the LT5 engine in which I use the 22. That's sort of like the AC42 or AC41 heat ranges.

 

[Vettehead Mikey]

For high-performance street use I submit that you always want use the coldest plug you can get away with, not the hottest.

Agreed.

 

[paul robb]

Thanks everyone, The ac 43 was what I was thinking. Just ordered a set from RockAuto....

 

[JohnZ]

Thanks everyone, The ac 43 was what I was thinking. Just ordered a set from RockAuto....

You'll wish you hadn't - they're WAY too cold for normal street operation. 44's haven't been made for decades; I've used 45 or R45S in all my small-blocks (including 11:1 327/365 Corvettes and 11:1 Z/28's) for twenty years or more, and they work just fine. 43's are fine for drag racing, road-racing, or other heavy-duty high-duty cycle use at high power settings, but they suck for normal street operation. Same goes for big-blocks - they thrive on AC R45XLS plugs for normal street operation. Unleaded fuel is the best thing that ever happened to spark plugs, but they'll still foul if you don't match their heat range to your driving style; not everybody drives all the time at WOT and 7000rpm.

 

[orlandjoe]

I have used Accel 576 for years with no problems. They cross-over to ACDelco R44.

 

[wallyknoch]

As usual, late to the Party

My owners handbook for the 62 specifies '46`s and the OE plug in my 61 283/315 was 44`s and not the "S" suffix....I don't recall what was listed for the 62, however I`m almost positive it was not a 43 and that too is a FI piece....

If I was the OP, I would use 'Johns reply as the correct choice and consider the question answered

 

[65TripleBlack]

Hib and Mikey are wrong again.

Owners' Manual states that:
43 should be used for severe duty and trailer towing and sustained highway use
44 should be used for "all around driving" and were OEM installed upon delivery
45 should be used for sustained stop/go driving

R45S would be my choice if I were committed to using an AC spark plug in the car.

My preference is the NGK XR4.........a non-resistor, extended tip, copper plug with "V-grooved" electrodes, which is in the AC "45" heat range.

 

[Vettehead Mikey]

Hib and Mikey are wrong again.

Love you too Joe.otfl

So you disagree with my advice above to go with the 45 heat range, or simply that I (erroneously) thought the car originally came with 43?

 

[65TripleBlack]

Love you too Joe.otfl

So you disagree with my advice above to go with the 45 heat range, or simply that I (erroneously) thought the car originally came with 43?

The latter.
You're not all wrong.................but almost always wrong.:L

Hib must enjoy cleaning and changing spark plugs.

 

[Vettehead Mikey]

wrong

wrong.................wrong.

Guess you won't be applying for any NCRS judging positions, huh? BTW- which years and engine options DID come with 43s? You must know.

 

[65TripleBlack]

Guess you won't be applying for any NCRS judging positions, huh? BTW- which years and engine options DID come with 43s? You must know.

Cryptic. Please explain?

 

[Hib Halverson]

Hib and Mikey are wrong again.

Owners' Manual states that:
43 should be used for severe duty and trailer towing and sustained highway use
44 should be used for "all around driving" and were OEM installed upon delivery
45 should be used for sustained stop/go driving

R45S would be my choice if I were committed to using an AC spark plug in the car.

My preference is the NGK XR4.........a non-resistor, extended tip, copper plug with "V-grooved" electrodes, which is in the AC "45" heat range.

I'm not sure what I was "...wrong again." about but I'll admit, when it comes to the technical aspects–including spark plug heat range selection–for show cars, waxers and trailer queens, "65TripleBlack" is far more knowledgeable than I.

I will point out, however, that the Owner's Manual recommendations above don't take into account the existence of unleaded fuel nor 46 years of advancing technology which, for one thing, has brought us copper-cored, wider-heat-range spark plugs.

I change spark plugs very seldom and never clean them. I haven't cleaned a spark plug since I scrapped my old, hand-held sand blaster. That was 30 years ago. The only car I own that even comes close to the kind of stuff "65TripleBack" understands is my old hot rod 71 Coupe. It sees some starts without warm up and has a camshaft that makes it idle in a manner which, if I didn't have the car's Holley 850 tuned properly, would foul plugs. I've used either NGK 6's or Denso 20s in that thing for years. They are about the same as the AC 42 heat range. I just put new Densos in it and that was the first set of plugs in that engine I'd changed since 1994. Maybe reason I get great plug life is the MSD ignition I have.

As for the heads on that old stuff, back in the day, when I had a 63 327/340, I would run the old NGK B6S on the street. It was one of the first copper core plugs you could get for Gen 1 SBV8s with cast iron heads and 13/16 hex 1/2-in reach plugs. I also had a 327 with an early F.I. on it stuck into a 65 Malibu. I ran the B6S in that, too. Back then, I was still using OE points and Mallory Voltmaster coils. I do not remember problems with fouling but, again, I was not driving show cars, waxers or trailer queens on short trips, ie: starts without warm-ups.

 

[65TripleBlack]

I'm not sure what I was "...wrong again." about but I'll admit, when it comes to the technical aspects–including spark plug heat range selection–for show cars, waxers and trailer queens, "65TripleBlack" is far more knowledgeable than I.

I will point out, however, that the Owner's Manual recommendations above don't take into account the existence of unleaded fuel nor 46 years of advancing technology which, for one thing, has brought us copper-cored, wider-heat-range spark plugs.

I change spark plugs very seldom and never clean them. I haven't cleaned a spark plug since I scrapped my old, hand-held sand blaster. That was 30 years ago. The only car I own that even comes close to the kind of stuff "65TripleBack" understands is my old hot rod 71 Coupe. It sees some starts without warm up and has a camshaft that makes it idle in a manner which, if I didn't have the car's Holley 850 tuned properly, would foul plugs. I've used either NGK 6's or Denso 20s in that thing for years. They are about the same as the AC 42 heat range. I just put new Densos in it and that was the first set of plugs in that engine I'd changed since 1994. Maybe reason I get great plug life is the MSD ignition I have.

As for the heads on that old stuff, back in the day, when I had a 63 327/340, I would run the old NGK B6S on the street. It was one of the first coper core plugs you could get for Gen 1 SBV8s with cast iron heads and 13/16 hex 1/2-in reach plugs. I also had a 327 with an early F.I. on it stuck into a 65 Malibu. I ran the B6S in that, too. Back then, I was still using OE points and Mallory Voltmaster coils. I do not remember problems with fouling but, again, I was not driving show cars, waxers or trailer queens on short trips, ie: starts without warm-ups.

Can you tell us what makes you say that?
Hint: I don't own a trailer.

 

[Vettehead Mikey]

Cryptic. Please explain?

Day 1, lesson 1 of judging school starts with a caution against use of the word 'wrong' when evaluating an owners vehicle. Tends to get the owners hackles up and does nothing towards explaining the judge's thoughts behind the deduction.

Our buddy in SW PA would have similar tact and diplomacy issues I think. :L

 

[65TripleBlack]

Guess you won't be applying for any NCRS judging positions, huh? BTW- which years and engine options DID come with 43s? You must know.

Day 1, lesson 1 of judging school starts with a caution against use of the word 'wrong' when evaluating an owners vehicle. Tends to get the owners hackles up and does nothing towards explaining the judge's thoughts behind the deduction.

Our buddy in SW PA would have similar tact and diplomacy issues I think. :L

You still didn't clarify the second, and more disturbing part of the cryptic message! I lost 2 nights' sleep because of it. Xanax, Sominex, whiskey and Tylenol PM did not produce the desired effect. I don't know if any 1950's or 60's SBC Chevies were ever delivered with AC 43 plugs installed. I doubt it, but, maybe the '67-'69 Z28 might be the exception if, in fact, what you intimate is true. The only reason I say this is because they were homogenized otflunder FIA Gr1 rules as delivered from the factory as race ready.

I used the word "wrong" to describe what you and Hib are. I could have also used the word "mistaken". I never use the word "wrong" when explaining a deficiency or "departure from original configuration" in a judging situation. I always state where the deficiency lies on any of the five (C D C I F) axes, and then state the departure from "original". Besides...................I always first blow smoke up their arse by gushing about how beautiful, rare, nice, cherry, desirable, significant, clean, their Corvette is before I systematically crack them like an egg...............................berate them and criticize their supposedly fine automobiles. I lull them into a false sense of security before I lower the boom on them.