Aluminum heads and autolite 3924's

[RyanSG]

Hey guys, changen my plugs and i was told to use the 3924's by a few people. I;m not sure what to gap them at since i'm running a turbo setup.. I was thinking .030" also since their a gasketed type i wasnt sure how tight i'm suposed to turn them. I have em in and i can still turn them but i didnt tighten them anymore since i'm scared of messing up my heads.... should they tighten up where they stop? Not overtighten but enough that they stop...... Just scared of messing up a set of $1200 heads....

 

[DMAN302]

I run those in my Eddy heads gapped at .054.

 

[RacEoHolic330]

Im running 3923's with my afr 165's. Work fine. With a power adder plugs should be gapped .030-.035. I have mine gapped at .035. As for tightening them, just tighten them enough so they won't unscrew themselves. You can put a little muscle into it, but don't go crazy, hah. Put some motor oil on the threads too. Are you going to index the plugs? I've heard you can pick up some power by doing that.

 

[Paul Perreca]

how do you index them - and I'm runnign Bosch right now - are they crappy? i dont know what my dad gapped them at - whatever it said in the book he said- but anyway - will changing to the autolites 3924's gapped at .054 help considerably? this one guy on here somewhere said he changed the plugs and gained 20 HP because the original plugs weren't mean for the aluminum heads, and they didn't stick into the chambers far enough or somethign of that sort...

THANKS

 

[QDRHRSE]

When I was running AFR185's that was the plug AFR told me to use. You might want to run the 3923 if you have a turbo. I think the 23's are a step colder.

 

[RyanSG]

yeah thats wht was happening to me i could tell it was running bad as well as i was getting smoke at idle. The bad part was i switched to a stand alone ECU and i figured it was just my settings... after comparing the stock type an the 3924's there about 2x as long into the head... I just hope i didn't mess up the threads or seats or anything be useing the stock non-O ring plugs when i shoulda had the 3924's in instead...

 

[RacEoHolic330]

here's some info on indexing plugs. I'm thinking about doing this when i change my plugs soon. It's logical

http://www.fordmuscle.com/archives/2000/07/indexplugs/index.shtml

Paul, I'm a fan of autolites, they're cheap and get the job done well. Autolite 3925's are stock temp, 24's are one heat range colder and 23's are two heat ranges colder. Are those bosches you have platinum? cause platinum is garbage. I don't think changing will make a huge difference, but you never know.

 

[Paul Perreca]

i'm pretty sure they are platinum - but if stock is 3925 and the ones we need are 3924 ... is the 4 and 5 the "steps colder" or the "depth into the head" ???

 

[RyanSG]

yeah the autolite heat rang is the last 2 numbers. Like paul said, 25 is stock or NA heat, then for boosted you go 1 or 2 steps colder 24 or 23.. The 39 i guess is the that designation for the length. All i know is i snugged em up and she fired right up.. the good part is i could go 3 notches leaner on my fuel map at idle and it;s soooo snapy now liek it used to. So it looks liek that was my issue so far.. Now i gotta see how it reacts under boost. Still gapped at .030 and so far so good. I've also herd from a lot of people that platnum plugs aren't good at least for boosted aplications, not sure about stock setups though..

 

[DMAN302]

auto light 3924's will work perfectly..they are the same as the champion size wise that Edelbrock recomends for their heads.

 

[04sleeper]

i'm pretty sure they are platinum - but if stock is 3925 and the ones we need are 3924 ... is the 4 and 5 the "steps colder" or the "depth into the head" ???

The end number is the heat range. The 39 means they are 3/4" longer for aluminum heads.

They do this because it gives the plug more thread to grip so you don't strip them in the aluminum.

If you are running a stock length plug in an aluminum head you could strip it and yes the plug is 3/4" too short and not going all the way into the head.


Be sure you use anti-sieze when putting them in as well.