AC-45 Spark Plugs

[David K.]

On my 65 L76-365hp; I currently have AC-44 plugs, (no idea how long they have been with the car) and am thinking of changing them soon. I have a full boxed set of NOS AC-45 plugs on hand. The 45's show up on the Tune Up chart as "hotter" plugs. What does this mean & how does it affect drivability ?
I drive the car around the back streets on short runs from Stop sign to Stop sign, with 411 gears. There's absolutely no highway or high speed long distance driving.
Thanks in advance.

[Timothy B.]

Re: AC-45 Spark Plugs

David,

FWIW, I would pull two or three of the plugs and take a look if they are sooted or clean, if clean I would leave well enough alone. Either plug works fine, the cooler AC44 will dirty up faster depending on how the engine tune is.

[Jeffrey S.]

Re: AC-45 Spark Plugs

On my 65 L76-365hp; I currently have AC-44 plugs, (no idea how long they have been with the car) and am thinking of changing them soon. I have a full boxed set of NOS AC-45 plugs on hand. The 45's show up on the Tune Up chart as "hotter" plugs. What does this mean & how does it affect drivability ?
I drive the car around the back streets on short runs from Stop sign to Stop sign, with 411 gears. There's absolutely no highway or high speed long distance driving.
Thanks in advance.

David,
A hotter plug will retain its heat longer than a colder plug. This means that it will burn off deposits for a longer time than the colder plug helping to keep them from fouling. The actual spark is no hotter than any other heat range. As long as you don't get any pinging, all is good.
Jeff

[David K.]

Re: AC-45 Spark Plugs

Thanks Guys; I inspected the car again his afternoon, and realized that I have had the AC45 plugs all along. Hence; I will remove a few plugs and check for any issues and simply leave them in place if all checks out. The car is running like a pig (rough idle after 3-4 miles, and then the engine dies....requiring restarts all the way home). It's been doing this since the beginning of the summer. The Holley carb was rebuilt last year by a reputable fellow from our hobby, and we have tried adjusting the carb mixtures repeatedly, but to no avail. Timing is properly set. Still a mystery as to why it's dying after just a few miles........

[Timothy B.]

Re: AC-45 Spark Plugs

David

That could be many different things from needing a tune up, points etc to other ignition problems like spark plug wires.

You gotta start with the simple stuff first, did this problem start after the carburetor overhaul? Do you recall the last time the engine was tuned up. When you set the idle mixture screws make sure the engine is good and warmed up, check the float levels. Try to eliminate as many things as you can by making sure all is adjusted well. When it restarts does it run up in rpm ok and then die out when it returns to idle.

[Duke W.]

Re: AC-45 Spark Plugs

For your driving conditions the AC 45 is the best heat range plug. The stalling issue could be due to percolation, which is a common problem with modern E10 fuel especially in hot weather, around town, stop-and-go driving. One thing you should do is wire open the heat riser valve. Also check the exhaust manifold temperatures with an IR gun with the engine idling after its thoroughly warmed up. It they are more than 500F there is something wrong with your spark advance map. Total idle advance at 900 (VAC connected) should be in the low 30s and total WOT advance should be as high in the 36-40 range as the engine will tolerate without detonation. A dead VAC is a common cause of high engine temperatures and percolation.

Do some searching. There have been many threads on the subject. Some have found that installing insulation sleeves around the fuel pipes in the engine compartment have helped, significantly.

Duke

[John F.]

Re: AC-45 Spark Plugs

Brain fart. What does the acronym WOT stand for?

[Ed S.]

Re: AC-45 Spark Plugs

Wide Open Throttle -

[David K.]

Re: AC-45 Spark Plugs

Thank you gentlemen; A full and thorough tune-up is in order when the car comes out of storage next spring. I'm running Shell super 91 gasoline with "no-ethanol" whatsoever & recently (summer 2018) added Sunoco non-ethanol off-road racing gas (96 0ctane) at a 50/50 ratio with the pump non-ethanol 91 octane. Maybe the new gasoline mix is causing the issues. Prior to this new mixture, I was running it with straight pump 91 no-octane with no issues. I will verify everything listed within your recomendations during the tune up, just to be sure.
Thank you.

[John F.]

Re: AC-45 Spark Plugs

Thanks Ed!

[Timothy B.]

Re: AC-45 Spark Plugs

Thank you gentlemen; A full and thorough tune-up is in order when the car comes out of storage next spring. I'm running Shell super 91 gasoline with "no-ethanol" whatsoever & recently (summer 2018) added Sunoco non-ethanol off-road racing gas (96 0ctane) at a 50/50 ratio with the pump non-ethanol 91 octane. Maybe the new gasoline mix is causing the issues. Prior to this new mixture, I was running it with straight pump 91 no-octane with no issues. I will verify everything listed within your recomendations during the tune up, just to be sure.
Thank you.

David, I would run that fuel out and go back to what was working to eliminate anything that could be suspect.

You just never know, the storage tank (not your car tank) could have water and rust inside because it may be old.

[John D.]

Re: AC-45 Spark Plugs

I have R45S in my 67 small block. The S is extended tip...working fine for the last 20 years.

[Edward B.]

Re: AC-45 Spark Plugs

Good suggestions by Duke. Perhaps the car is simply not driven enough. Make sure the points are clean. Give it a good run on the highway accelerating vigorously through the gears. You'll be surprised by the benefits that can be had from a little exercise.

[Duke W.]

Re: AC-45 Spark Plugs

Back in the day we referred to that as an "Italian tuneup".

Duke

[Elliott P.]

Re: AC-45 Spark Plugs

Uhhhh..., has anybody checked the fuel pump pressure and flow rate (and fuel filter)?