The Stovebolt Site Forums The Shop Area Engine Shop 235 , Good compression, black sooty plugs, runs good

As long as we are all overthinking spark plug choice…

Has anyone here had any actual experience with the R45 being “too hot” of a plug for extended highway or other hard use?

OK. I had to go back and look at my manuals to see what plugs are what.

My Toronado, Cadillac, and AD Chevy all specify AC-44 in their respective shop manuals. The Chevy manual actually specifies AC-44-5. Does that mean AC-44 or AC-45?

Whenever I tried to buy plugs for any of them, I've been told AC-44 are not available and that AC-43 is the substitute. The AC-43 is the plug that comes up for these vehicles when I try to buy them online from various places.

So... I did confuse AC-44 with AC-45 in my first post (which I have since deleted to avoid confusing the issue even further).

But, the question remains, which plugs are actually discontinued and which ones are still available, discontinued or not?

"Hot" plugs of any manufacturer's production have a tendency to erode the ground lug and sometimes give the ceramic insulator a shiny, blistery appearance when they're used for extended highway driving. That's been my experience over several decades of tuning carbureted engines. Modern fuel injected engines with computer controlled ignition timing, high voltage ignition systems, and almost instantaneous fuel mixture monitoring make spark plugs last about three days past forever. I'm getting ready to change plugs and coil packs on my 04 Ram 1500 4.7 liter engine- - - - -60K miles on the plugs, and almost 300K on the coils.
Jerry

It looks like the AC-44 is the one that's discontinued. There are a bunch of AC-44xxx available but the suffixes indicate that they're extended reach or whatever. They're not the original spec AC-44.

The AC-45 appears to be available. Rock Auto has them on sale for $.50 off right now at ~$1.30 each.

I know the R45S has been recommended by some here. It’s possible one of the extended reach R44 variants might work.

There’s an AC Delco version plug decoder if you plug that into a search engine. The R44F looks like a possibility? More measuring and verifying would be needed.

I've never wanted to experiment with plugs that don't look exactly like the ones that came out of the engine from the threads to the tip. I'm afraid the piston will hit them and ruin the engine.

Try making a "positive stop" for finding top dead center on a stovebolt engine. It's necessary to put an angle on the threaded rod that's in the spark plug shell or it never touches the top of the piston. Extended tip plugs on a stovebolt have exactly zero risk of touching a piston crown. Just make sure no threads on the plug shell stick into the chamber, even if they have to be machined off. Hands-on experience trumps even an "educated guess" every time.
Jerry

Yes, I see what you mean. I was referring to engines in general. I never want to guess with something that could potentially ruin an engine.

On the Stovebolt, you're saying that if the only part of the plug that's extended is the electrode/insulator and that the threads and seat are identical to the stock plugs, they'll be ok with no interference.

Yes, and even if a thread or two extends into the combustion chamber, it's a simple machining procedure in a lathe to shorten the threads. Carbon-caked threads can damage the cylinder head when the old plug is removed. On some of the race engines we built, we used a hand-held cutting tool to alter the gasket surface of the plugs to "clock" the ground electrode to an identical position in all the combustion chambers. That's really getting anal-retentive!
Jerry

Update - I installed the new AC Delco R45S spark plugs , and as Jerry said... no issues . I'll put a few miles on it and pull a couple plugs to see if there's any change in perceived sooty appearance problem.

52Carl - on the fast idle issue , I made sure the throttle cable wasn't interfering with the eyelet, put a couple drops of marvel mystery oil on the eyelet area, made sure throttle knob in the cab was fully pushed in. No problem with fast idle on my test drive. Not once.

So after all of the deep dives, overthinking, fixing what wasn't broke ....I think I'll just drive it.