which spark plugs to use

[Andyboy]

My v6 305E has AC 45xls on driver side and AC 45s spark plugs on pass. side. Which ones should I stick to, maybe there even the wrong ones. All you V6 305ers please help. What are you guys running on your 305's. Thanks

[1Bad62Pro/Street]

Originally Posted by Andyboy

My v6 305E has AC 45xls on driver side and AC 45s spark plugs on pass. side. Which ones should I stick to, maybe there even the wrong ones. All you V6 305ers please help. What are you guys running on your 305's. Thanks

Spark Plug - AC - C45NS maybe???
http://67-72chevytrucks.com/vboard/s...d.php?t=433505

http://www.google.com/custom?domains...D%3A1%3B&hl=en

http://talk.classicparts.com/showthread.php?t=404

[Andyboy]

OK the cross reference for the AC45xls in autolite is the autolite66. The difference between the AC45xls and the AC45s is the reach. The 45s' are hi-pref. and there fatter and shorter thread. Maybe someone here can tell me why someone would put these to different sparkplugs. Maybe something to do with the cylinders? I don't know just guessing hope someone can help. Thanks

[Rich 5150 69]

Probably couldn`t find matching plugs,,,best guess...

[1Bad62Pro/Street]

Andyboy,

Jump over here at 6066 GMC Trucks:
Information About Spark Plugs
http://www.6066gmcguy.org/SparkPlug.htm
GMC Big Block V6
www.6066gmcguy.org/gmcv6a.htm
http://www.6066gmcguy.org/GMCTruck.htm

[Andyboy]

Originally Posted by 1Bad62Pro/Street

Andyboy,

Jump over here at 6066 GMC Trucks:
Information About Spark Plugs
http://www.6066gmcguy.org/SparkPlug.htm
GMC Big Block V6
www.6066gmcguy.org/gmcv6a.htm
http://www.6066gmcguy.org/GMCTruck.htm

Yeah the site is set-up different just too many email, or i was just in the wrong place. Thanks anyways.

[GJB]

Old thread, but curious if someone had an answer for this question as I have the same one. Just looking for the correct Delco plugs.

[MusicMan70]

Here is some info from one of the threads over at 6066GMC about the long and short threads on the plugs.

https://6066gmcclub.com/showthread.p...ht=spark+plugs


and an explanation excerpt:

the fact that 73-74 379, 432 and 478M V6 engines use a short tapered plug which was originally the AC R43T plug superseded by the AC 10 plug which I have a set of and will probably never use. Other factors to consider is the newer big cubic inch head has larger valves than the stock 305D head. 379's share the same intake valves with later 305E engines(305D have smaller valves) and have the larger Magnum Sodium filled exhaust valves, while the 432 and 478 heads have the larger Magnum intake valves over the 379. To find out which later model head you have a look at the intake and exhaust port sizes will determine that. 379 heads have the smaller ports like the 305. 432 & 478 are the big port Magnum heads, I think your best bet is to find a matching set of heads. I would also like to mention that not all 73-74 478M engines used the short tapered plugs. A replacement crate engine built in 73-74 could have the 3/4 long reach plugs for older applications. I have a late 73 478 that came out of tilt cab TM7500 series with the short tapered plug while the 74 478M in my 68 was a new replacement crate engine that came out of a 63 6500 series tilt cab and came with the 3/4 long reach plugs

RockAuto has these AC Delco plugs listed

https://www.rockauto.com/en/catalog/...park+plug,7212