This is an 88 Camaro that someone put a SBC into, I assume. It currently has Autolite AP3924 plugs that look a bit worn so I'm looking for replacements in either AC Delco or maybe Champion. A cross referance says AC Delco 5 is the equivalent plug. Any others to consider? This is just for street use.

 

Delco, NGK, Bosch, or any other top brand is fine. Stay away from gimmick plugs like E3. Gap accordingly.

 

What heads? What compression?

 

Gap according to what? .035 reasonable?

 

No idea. I didn't build it.

 

Stay away from champion.

I run a delco fr3ls or fr5ls, depending on what im doing.
Not sure what the new number is

 

I run NGKs, mainly because that is all I run in powersports and have never had issues with them. Like mentioned above stay away from the fancy plugs, not worth the money. Delco is good too for these. Best thing you can do is figure out what heads you have and look up what that manufacture specs for them then find the cross references.

 

I assume the previous owner knew all that when he installed the Autolites and they cross to AC Delco 5, https://www.rockauto.com/en/moreinfo...t=7212&jsn=779 They show a gap of 0.045.

 

Be careful making assumptions on previous owners doing what is correct. More times than not, they don't. Those look like aftermarket aluminum heads. Do they have any markings at all on them? Most have something etched into the front/rear accessories mount location areas.

 

As stated, you have to determine what heads they are to ensure you have at the correct type of spark plug.
I've seen a short threaded plug in a long threaded hole. I even seen a tapered plug where a gasketed plug is supposed to go. So you never know.
You might have to pull a valve cover to look for some I.D if there are are no identifiable markings on the ends of the heads.

 

Gotta know what the heads are. No way around it. If you don't know, FIND OUT. LOOOOK.

There's washer seats and tapered seats, and various possible thread lengths. Disaster ensues when some wrong combos are mis-matched.

More to this question than what brand people like.

Gap is a trivial concern. Yes/No: yes you need some; no the engine won't work without some, butt how much doesn't make much difference most of the time. The wider the gap, the more A/F mixture is exposed to the spark, butt also, the weeeeeeeker the spark, and the more stress it puts on the ignition system since it makes the voltage developed across the gap higher. Anything from .035" to .045" is fine for most applications.

 

Pro Port heads?

 

I think those are a knock-off of GMPP's fastburn heads, minus the angle plugs. Crate engines with those heads came with these:
They're a marine plug, and a bit cold, but good. I'd give them a shot.

 

What's wrong with staying with the Autolites? I'm using the 3924s in my 383, and they work fine. That plug is a pretty middle of the road option. Should be extended (.75") reach gasket seat which is pretty common for SBC aluminum heads. If those plugs didn't smack the face of the piston, then they are most likely the correct reach and seal design.

You're not going to gain any performance between those and the most expensive multi-electrode spark plug ever made with unobtanium and children's tears. Stick with what works, and in that case, you're looking at pretty basic, cheap plugs. Gap them to .035" or .045" and send it.

 

Therein lies the rub. Whose to say that the Autolites removed where of the correct style? Heat range notwithstanding, it's the reach and seat profile you mention that haven't been determined. It's entirely possible that the wrong plug type could have been installed when the OP received them.
I've seen it firsthand.

 

If the car is running then whatever was in it is likely the right one. If the reach was off they'd be beat. Spark plugs are one of the parts where price really doesn't matter and 'gains' are mostly snake oil.

 

What I can say is that I came across a set Vortec heads that had short thread plugs installed. Ran fine but most definitely not an ideal situation with the plug shrouded by a 1/4". I surprised that it ran at all really but it did.
Another was a set of aluminum heads that had tapered plugs in place of what should have a gasketed one. Those heads unfortunately were damaged as a result.
Just saying.
It's easy enough for the OP to get in there with a flashlight and determine the length and seat type. Why guess?

 

For quality I prefer AC and NGK plugs. Just my opinion but they have always worked well and lasted long time. Like others have said, gap is not a big deal. What IS a big deal is following up to ensure you have the proper heat range. Whatever plug you go with make sure you pull a few to check tip color, oil buildup, etc to make sure you have the proper heat range.

 

Do you have headers? If so, then you will probably need a shorty header plug, which will severely limit your choices.

 

NGK 5155 FR4 V power plug