L-78 Spark plug choice
 

What do you guys find is the best plug to use in the 69 840 heads. Someone mentioned NGK. I'm doing everything I can to keep the 69 L-78 ElCamino correct, but if there is a plug that works better than the AC's. I guess I can deal with that. Brand? Part# Where to buy?

Re: L-78 Spark plug choice
 

Stash your NOS AC's in the trunk for bragging rights, but run the NGK's! https://www.yenko.net/ubbthreads/imag...ns/naughty.gif

Re: L-78 Spark plug choice
 

I can't seem to be able to figure out which NGK plug (part#) would be used for a 69 L-78 application. I need a part number, so I can walk into an auto parts store, and order them from a 20 year old who thinks a Chevelle is made by Ford.

I found GR5, GR5GP AND GR5IX, for 69 L-78.... Any one know which would be the better one to use?

Re: L-78 Spark plug choice
 

Bill, If you have your AC number they can cross reference that on the computers (I work PT at Advance) and that will give you some NGK numbers. Believe it or not we still have books and catalogs behind the counters but alot of the newer/younger employees haven't been introduced to them. If you can get one of the guys/gals to pull the spark plug catalogs, they have lot of information about heat ranges and numbering systems. I sell a lot of plugs to racers, they buy several heat ranges and try different brands. I even go through boxes of plugs with one guy while he finds the ones that index the best for him. he is nuts.... But very fast... I will be at work tomorrow, PM me with some numbers and I will look up some stuff for you. I stock and can order the Autolite racing plugs if anyone needs them too.

Tommy (believer in the catalogs) https://www.yenko.net/ubbthreads/imag...ins/3gears.gif

Re: L-78 Spark plug choice
 

NGK,you want be dissappointed.the ac delco have had issues in the past;been there .chris teed

Re: L-78 Spark plug choice
 

NGKs are the ticket!!!!!! I had nothing but problems with the AC Delcos in my 396/375HP Motor, engine would miss at around 3,500 RPM.. The NGKs "woke up" the combustion chamber. Engine runs much better!!

I bought mine at the local parts store, Advance Auto Parts, and I think they were around a buck a piece.. Well worth it!!

Rich

Re: L-78 Spark plug choice
 

OK done deal. I went to Advance, Auto Zone and neither could find what I wanted in their comp or a book. I had to start by telling the "girl" that a Chevelle was a Chevrolet!! I just had to leave. I went to Google and found, what else but, Sparkplugs.com. They were shipped within an hour. Should be here ina few days. Thanks for the help.

Re: L-78 Spark plug choice
 

Base plug for L78 is NKG-2851, $2.38 @ Summit Racing the other day.
Mike

Re: L-78 Spark plug choice
 

OK guys!

While we're at this topic, what would be the correct NGK plug for a '69 L/89?

Nuch

Re: L-78 Spark plug choice
 

Try NAPA. Forget about Advance, Carquest, Pep Boys, etc.....

Re: L-78 Spark plug choice
 

I've always run the AC43N plugs in our L78 with zero problems. About 20K miles on the last set. NGKs lasted in our old snowmobiles when nothing else would. Everyone who uses them like them.

Re: L-78 Spark plug choice
 

Sorry I'm late to the party...maybe I need to make an NGK plug reference post a sticky? LOL!! Anyway...

5671 is the gasketed plug for the 840 head ('69 & earlier)
UR5 is the tapered seat plug for the 291 head (late '69 & later)

I run a 5671-7 in our Camaro...the -7 part is the heat range, and NGK plugs are rated backwards of most plugs in that the bigger the heat rating number the cool the plug...Autolites are 'ok' plugs, but stay away from Champions or AC's...

Re: L-78 Spark plug choice
 

Autolite number 26, never had any problems ever. Not only is it fun to watch the "counter information engineer" look up a 69 chevelle 396 375 horse, try telling them it has a 427 and watch the fireworks. https://www.yenko.net/ubbthreads/imag...ns/shocked.gif https://www.yenko.net/ubbthreads/imag...lins/dunno.gif https://www.yenko.net/ubbthreads/imag...s/confused.gif

Re: L-78 Spark plug choice
 

While we are on the spark plug subject,what about a 1968 302 Z28 plug ?

Re: L-78 Spark plug choice
 

What about the 842 aluminum heads?

Re: L-78 Spark plug choice
 

I even run the NGKs in my jet ski which is a two stroke motor. never had any foul yet!!!

Rich

Re: L-78 Spark plug choice
 

firez: the Z28s use the XR5 plug I believe.

Chris: if I'm not mistaken, the 842s use the R5671 also...but not sure on heat range? Maybe go colder (like -9 or -10?), but maybe Sam or someone else familiar with the alloy stuff can jump in here.

Note to self: make NGK plug crossover sticky post... https://www.yenko.net/ubbthreads/imag...ins/tongue.gif

Re: L-78 Spark plug choice
 

Thanks for the Z28 plug advise.

Re: L-78 Spark plug choice
 

I thought I had an NGK cross ref - but I can't find it. This might help though - you can cross ref your AC to Champion, then back check the Champion number to NGK.
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Re: L-78 Spark plug choice
 

I believe the Champions used to be preferred by racers because you could read the heat bluing color on the shinny threads. It's hard to get a true reading on the porcelain on a fresh set if the car is running good. (that's my feeling) but my racing buddy likes to put in a fresh set then pull them at the top end of the track before driving back to the pits. I guess I shouldn't argue with his wisdom.

Verne https://www.yenko.net/ubbthreads/imag...iggthumpup.gif

Re: L-78 Spark plug choice
 

After much reading, I have *yet* to find any charts that agree on corresponding part/stock numbers, and the cross reference charts are all different it seems also. But here's what I could dig up from my AC book and the NGK site...(NGK #s below are listed as part number/stock number, hottest plug @ top)...

<u>Z28 &amp; LT-1 with 186 heads:</u> my AC book calls for a C43 or an R43 plug, and the NGK site says-

Standard, V-power (3/8" reach, 13/16" hex, projected tip, gasketed seat):
XR4 / 5858
XR5 / 3332

Race, V-power (3/8" reach, 5/8" hex, projected tip, gasketed seat):
R5670-6 / 4449
R5670-7 / 5034
R5670-8 / 5657
R5670-9 / 6468
R5670-10 / 6702

<u>L78 &amp; L72 with 840 heads:</u> my AC book calls for a R44 or a 44N plug, and the NGK site says-

Standard, V-power (3/4" reach, 13/16" hex, projected tip, gasketed seat):
GR4 / 2635
GR5 / 2851

FR4 / 5155 (same as GR plugs, except for 5/8" hex)
FR5 / 7373 (same as GR plugs, except for 5/8" hex)

Race, V-power (3/4" reach, 5/8" hex, projected tip, gasketed seat):
R5672A-8 / 7173
R5672A-9 / 7405
R5672A-10 / 7942

R5671A-7 / 4091 (same as 5672, but with non-projected tip)
R5671A-8 / 4554 (same as 5672, but with non-projected tip)
R5671A-9 / 5238 (same as 5672, but with non-projected tip)
R5671A-10 / 5820 (same as 5672, but with non-projected tip)
R5671A-11 / 6596 (same as 5672, but with non-projected tip)

<u>L78 &amp; LS6 with 291 heads:</u> my AC book calls for a R43T, and the NGK site says-

Standard, V-power (.460" reach, 5/8" hex, projected tip, tapered seat):

UR4 / 6630
UR5 / 2771
UR6 / 7773
YR5 / 7052 (same as UR plug except w/ non-projected tip)

Race, V-power (.460" reach, 5/8" hex, projected tip, tapered seat):

R5674-6 / 4449
R5674-7 / 5034
R5674-8 / 5657
R5674-9 / 6468
R5674-10 / 6702

R5673-6 / 2405 (same as 5674, except w/ non-projected tip)
R5673-7 / 2817 (same as 5674, except w/ non-projected tip)
R5673-8 / 3249 (same as 5674, except w/ non-projected tip)
R5673-9 / 3442 (same as 5674, except w/ non-projected tip)
R5673-10 / 4050 (same as 5674, except w/ non-projected tip)

Re: L-78 Spark plug choice
 

I have a chart somewhere listing the AC spark plug coding. Off the top of my head, the "N" designates a long reach plug. "T" is for taper seat. "S" is for extended tip. There was other stuff as well. Any sparkplug problems that I ever had stemmed from carb problems, carbon tracked distributor caps, or bad plug wires.

Re: L-78 Spark plug choice
 

The "N" suffix means it's the same 3/4" reach, but only 3/8" threaded, as opposed to the "XL" like the 074 heads got that has 3/4" reach and is fully threaded.

https://www.yenko.net/attachments/322679-plugs.jpg

Re: L-78 Spark plug choice
 

[ QUOTE ]
Bill, If you have your AC number they can cross reference that on the computers (I work PT at Advance) and that will give you some NGK numbers. Believe it or not we still have books and catalogs behind the counters but alot of the newer/younger employees haven't been introduced to them. If you can get one of the guys/gals to pull the spark plug catalogs, they have lot of information about heat ranges and numbering systems. I sell a lot of plugs to racers, they buy several heat ranges and try different brands. I even go through boxes of plugs with one guy while he finds the ones that index the best for him. he is nuts.... But very fast... I will be at work tomorrow, PM me with some numbers and I will look up some stuff for you. I stock and can order the Autolite racing plugs if anyone needs them too.

Tommy (believer in the catalogs) https://www.yenko.net/ubbthreads/imag...ins/3gears.gif

[/ QUOTE ]

Exactly. I've been working at Advance PT since '01, primarily to get discounts. The concept of a catalogs are vague to 80% of the people that work in the store. The only people that really use them are me, and the store manager. I have no clue why parts places hire people who have computer skills but no part/car knowledge. On old vehicles 90% of the parts aren't going to be on the computer. For those of you who don't know, advance has an interactive website with a full catalog system that is really easy to use to help you find parts. Most parts have images as well. Typically you can find more parts for your car online than the people can in the store. Find the part # you need online, then take it to the store with you and have them order it, or get it off the shelf. It takes all of the guess work out of it, and you get the right part the first time. https://www.yenko.net/ubbthreads/imag...iggthumpup.gif

NGK's are good plugs, like everyone has previously stated. I ran champions and autolites in my built 340 thats in my cuda and after 3 or 4 trips around the block, it would be skipping or missing. I put a set of NGKs in it about 4 months ago and have been trouble free since then. Colder plugs really helped my motor out.