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