Spark Plug Recommendation

[Duke W.]

Re: Spark Plug Recommendation

As I said GM engineers know what they were doing.

If engineers are infallible as you suggest then why have something on the order 15 million vehicles been recalled in the last couple of years? Of course, back in the sixties recalls were rare. We were pretty much left on our own to figure out why spark plugs fouled and why the '63 340 HP engine had idle stability/stalling problems. (A VAC that didn't pass the Two-Inch Rule was the cause.)

At best the manufacturers wrote TSBs, but most got filed and forgotten by dealers, so we never heard about them. Customers were left on their own to solve many problems or, if lucky, they might find someone who had figured it out.

Duke

[Gene M.]

Re: Spark Plug Recommendation

If engineers are infallible as you suggest then why have something on the order 15 million vehicles been recalled in the last couple of years? Of course, back in the sixties recalls were rare. We were pretty much left on our own to figure out why spark plugs fouled and why the '63 340 HP engine had idle stability/stalling problems. (A VAC that didn't pass the Two-Inch Rule was the cause.)

At best the manufacturers wrote TSBs, but most got filed and forgotten by dealers, so we never heard about them. Customers were left on their own to solve many problems or, if lucky, they might find someone who had figured it out.

Duke

Mr Duke
Please stop turning this into a pissing contest. The original posting was for a 327 L79. And I answered in that light. But if you profess to have all the answers contrary to GM engineering you have definitely shared that. When the original poster request suggestions on plugs and yours is different from the original manufacturer then it is only your opinion. Understand others may not share your opinion. I said nothing of GM engineers being infallible. You stated "I found out back in the sixties that the AC 44 is too cold for normal driving and constantly fouled." Well I disagree, and did not have that issue. A situation that was not shared by the major population of 327 GM cars on the road at the time. Thank you for your opinion but it is just that, an opinion.

[Stuart F.]

Re: Spark Plug Recommendation

I guess, as I recall, always ran the 44 heat range in my 63 L-76 (340hp), but I did have fouling problems until I changed to electronic ignition(s). I first ran a Prestolite unit for a number of years, but it had too many wires with connection problems. I have since been running first a Pertronics I until around 2005 (which was just ok), and then their Pertronics II since 2005 until present. I have no fouling issues and it can recover from flooding and bad gas to run back up to redline at will. I have had AC44's in the engine for the past 12 years and have logged an average of 1000 miles/yr over that time. The last time I tried 45 heat range the engine ran poorly and the plugs looked like they were running too hot when I pulled them out. Could just be my type of driving or what I don't know. I don't claim to be an expert, I just know what works best for me.

Stu Fox

[Mark E.]

Re: Spark Plug Recommendation

I think all of the posters have a valid point. There are so many factors that determine the best heat range, so it's a matter of adjusting to what engine is telling you.

Duke- Regarding you statement: "Why do you need a "100,000 mile" spark plug on a vintage car that is only driven a few hundred to a few thousand miles per year?"... Good point. My thinking turned the logic around with a different conclusion: Why don't you use a "100,000 mile" spark plug on a vintage car if that increases the odds of never needing to change them again?

[Duke W.]

Re: Spark Plug Recommendation

There are so many factors that determine the best heat range, so it's a matter of adjusting to what engine is telling you.

Not true! The only thing that determines spark plug heat range is average load for the type of service. The lower the average load, the hotter the plug needs to be to keep the insulator above the approximate 750F required to preclude excess deposit buildup. My experience with Corvette engines, whether a 283/230 or 427/435 is that the OE installed heat range is too cold. John Hinckley has said the same thing over the years, and we both recommend AC heat range "5" or equivalent for normal driving including extended freeway runs at 80 MPH.

About the only way you can place full load in a road driving for more than a few seconds at a time is doing something that's likely unsafe to you and the motoring public.

But if you go to a racetrack hot lapping event you better install heat range "3" or even "2", to keep insulator temperature below about 1650F. At or above can cause preignition that can rapidly lead to destructive detonation.

So what other "factors" do you think need to be considered?

Removing spark plugs for inspection and troubleshooting is common on vintage engines. You may be able to ignore "long life" plugs on a new car engine, but they have better fuel and oil control, and much higher per spark energy that can bridge the expanded gap of worn electrodes.

The other issue is seizing. Aluminum heads are more susceptible, but it can happen on cast iron heads too, so I typically plug plugs for inspection about every 15K miles, but I've gone up to 30K on modern cars that have typical "two-dollar" plugs with a change interval of 30K miles, and they looked they they were good for at least another 30K miles.

Duke

[Timothy B.]

Re: Spark Plug Recommendation

I think heat range 5 is a better choice but I will give something to think about FWIW.. If the car spends lots of time running on the idle circuit (low speed and idle speed), make sure the carburetors throttle blade position at idle is set correctly. The best primary throttle blade setting is to just expose the primary transfer slot so it's just kept active, to much slot and the engine will run rich. Give the engine additional idle air from the secondary blades and then adjust the curb idle emulsion screws for best idle. If you need to slow the engine after that close the secondary blade and don't touch the primary blade position screw.

The transfer slot will allow a rich mixture into the engine at idle but also when the engine is decelerating.