It’s the Chevy 396, baby – one of the early darlings in the Mark IV engine family. Sure, it’s more niche than its brother, the ever-popular 454.

So what? A 396 is still as exciting and high-performance to base your retro-revival project on.

Let’s talk spark plugs here. A soft agreement is that the best spark plugs for 396 Chevy come from ACDelco or Champion.

An example would be the ACDelco R44XLS for casual/stock projects.

In general, Delco’s XLS family (R43, R44, R45) is a staple depending on your hot/cold plug needs. Champion’s RN12YC is the most optimal alternative, equivalent to the AC R43/R44 setups.

Here’s a quick table comparison before taking it further:

There are some design/power differences among the 396 family, too. Your choice of spark plugs might depend on these so let’s cover them.

396 setups follow a similar logic to what I’ve written about 454 big block spark plug options. ACDelco is the staple here just because back then, they specialized in those classic Chevy applications.

The crucial difference is that the 454 used the R4xT/R4xTS plugs. The 396 Chevy uses the R4xXLS design.

Make no mistake – these are not interchangeable.

Speaking in OEM terms, the AC R44XLS is the most optimal stock replacement on the lower 396/325 hp or 396/350 hp variations. The colder AC R43XLS is great for the more powerful 396/375 hp engine.

The logic is simple: You get colder plugs when running a hotter engine. If you’re doing a drag/strip-focused 396 setup, then you need to cool things down with a colder plug.

Conversely, if you’re OK with something more casual/a town cruiser, you’d need hotter plugs.

There are two popular alternatives to the R4xXLS options. First comes Champion with its RN12YC spark plugs.

The RN12YC is a high-quality copper plug that’s a direct OE fit. It’s pretty much Delco R43/R44XLS in terms of performance and capacity.

While not as close as the Delco-GM relationship throughout the decades, Champion is still a reliable American brand. Edelbrock has actually vouched on their RC series for improved clearance.

Note: I’ve seen some people also use Champion’s RN14YC which on paper should be a colder plug. I have no opinion whatsoever on these, though.

Another alternative comes from ACDelco again: that would be the RapidFire #4 plugs.

These are some juicy platinum goodness, with better corrosion resistance and improved longevity. The RapidFire family is advertised as performance-oriented and some people believe them to be more powerful.

In reality, most of the people I’ve talked to didn’t really feel that much of a difference.

They’re still a great option for more ambitious Chevy 396 projects, however. Grab a few if you don’t like the R4xXLS family for some reason.

(Or if you prefer platinum to copper for the more durable construction a.k.a. longer life cycle).

This can be a highly personal preference and depends on several additional factors, so I suggest you head over to some forums for extra opinions.

That said!

Generally speaking, most setups would fall between the .035 to 0.45 threshold.

The .035 is as vanilla (stock) as it gets. I’ve seen some people setting their spark plugs to a .040 gap with OE to lightly modded setups.

If your setup runs an HEI, you might consider stretching things out to 0.45.

From what I’ve heard, some earlier GM tips involved going as high as 0.50+ with HEI but that turned out to cause issues. So don’t go overboard with the spark plug gap, or else you’ll be needing a new pack soon enough.

Your 396 Chevy spark plug choice can also depend on what castings you have on your engine’s heads.

In reality, there are two variations: one that accommodates the shorter 5/8’’ plugs and one that nests the longer 13/18’’ plugs.

Practically speaking, though, the majority of 396s use the 5/8’’ type. The long-reach 13/16’’ are quite niche and found on very few specific applications.

The XLS design from the Delcos is a step-up, quite similar to how the TS in 454 plugs came to be. Both date back to the original big block spark plugs, the R43/44N.

The N-design was quickly found to be lackluster in terms of airflow, cold starts, and temperature control. XLS plugs have better temperature balance on different RPMs.

The updated design allows for a cleaner running 396, no matter whether you let it run cold or hot on your Chevelle (or vehicle of choice).

I mention Chevelle because I think a lot of us are suckers for a 396-running one. Here’s a great showcase video of a ’70 Chevelle SS 396. Its beauty is amplified by the guy running a Flowmaster Super 10 on it:

Hopefully, that was a helpful post 🙂

I wouldn’t say that the Delcos or Champions are the only viable choice. I’ve seen some people running Autolite plugs, too. In general, I’d stick to US plugs. The logic is similar to what I described in my post on Asian car spark plugs:

Back in the 60s/70s, overseas brands didn’t interact that much with classic American engines. GM collaborated closely with ACDelco, and other American manufacturers orbited around.

The Japanese automotive miracle hadn’t started yet; logistics globalization hadn’t fully kicked in either.

That’s just about it. Maybe you can find an NGK alternative or some of the newer brands. But a classic vehicle warrants a classic approach, and the brands I mentioned are the best at doing that.

For more Chevy big block guides, you can check my recommendations for 454 carbs. Some of the pointers there might be viable for a 396 engine too.

As always, I welcome any comments. Let me know what kind of setup you run, be it a Chevelle, Corvette, Camaro…you catch my drift.