View Full Version : Spark Plugs F11 vs F14Y

02-10-2015, 09:14 PM
Anyone ever had a discussion on the topic concerning the F11Y and F14Y spark plugs?

"For driving the V8s, the F14Y will give much better satisfaction and longer life & all around service & possibly better gas mileage.
The F11Y was what Ford recommended.

But it is too cold for most applications. If you drive this bird hard or race it, the F11Y may be a better choice, but for normal driving it is to cold."

What do you folks think?

Thanks, Neil

02-10-2015, 11:34 PM
Spark plugs are one of those things that I haven't given a lot of thought to. I imagine there was a good reason why Ford went to the F11Y in the FE's rather than the F14Y that was used in the Y blocks. I'm sure there's some type of scientific formula that has something to do with heat range and engine displacement. Maybe Dave can shed some light on it.


02-11-2015, 12:28 AM
I can. Heat range is important for combustion. The hotter the plug, the sooner it fires (to a point). If you choose a heat range that is too hot the plug may damage the porcelain or electrode.

So, what makes a plug hot or cold? Simply put, it's the amount of porcelain that is exposed. Porcelain retains heat better than metal so it tends to stay hot. Normal heat range is between 500C and 950C. At 500C the plug self-cleans carbon from the porcelain. Below that temp, carbon sticks and makes an electrical path called a 'carbon trace', causing the plug to foul. If the plug operates around 950C, the porcelain get so hot your engine will suffer from pre-ignition meaning, the cylinder will 'fire' before the spark is sent.

These important factors play a big role in this balancing act; air-to-fuel ratio, timing and spark plug heat range.

Making your mixture rich does two things, it slows the burn because too much fuel is harder to ignite and the unburned gas cools the engine. Retarded spark timing also delays the burn. At the expense of horrible gas mileage these two settings can lower your engine's temperature and deliver less HP. Since Squarebird engines were built to run leaded high-octane fuel that we no longer have, many owners are happy to sacrifice a little gasohol and lower HP just to make their engines run cooler. That is NOT what they were designed for.

Modern EFI engines constantly monitor exhaust gasses (with oxygen sensors) which tells the computer how rich or lean the engine is running. In turn, the computer adjusts the injectors AND ignition timing for the optimum 14.7:1 air-to-fuel ratio and the most HP output. As your foot works the gas pedal, this is a constant 'hunt' your computer does to maintain this ratio.

In a carbureted engine, a 'cold' spark plug never helps ignite the mixture, the porcelain operates too cold, and it permanently fouls from carbon traces. A 'hot' plug promotes pre-ignition and can damage the porcelain and electrode. It's best to operate with the designed plug for your engine. You can try different heat ranges, but keep a 'standard' set close. - Dave

02-12-2015, 10:21 AM
I have been in discussion with an old time Spark Plug guy (Don M.). I'll try to get him signed up as a member.
In the meanwhile here some insight from him that I thought I would contribute on his behalf, makes for good reading:

"The F11Y & the F14Y have been around a long time. I cant say when the F11Y was first introduced but it had to be after 1948-50. The F14Y stats & blueprint was issued to the factory 1954.

Somewhere I have a copy of the blue print issued to the factory dated late in December 1954. So first production would have been 1955. The F14Y replaced the (860 or 870) I can't remember which one. Sometime in 1953-54 Champion stopped black oxide and went to cadmium plating and remained that configuration.

Any spark plug mfg. by the US manufactures after 1978 no longer had the bottom of the insulator glazed. Because of this, they have a short life in vehicles with carbs. They did not need to in the computer controlled vehicles. There is no choke to stick, no chance of flooding and no carb to run rich.

Since the older cars had no protection from this, they tend to not last very long. The plugs become contaminated & may look good, but wont work. I assume since Champion redid their numbering system 1948 thru 1950 the F11Y & F14Y probably have the same birthday.

I would warn you the earlier bottom glazing is not always easy to tell. It was not always glossy. In fact some are very had to tell unless you are very familiar with it. While you may not get away with the F14Y in judging, it is still my contention the F14Y a better operational plug.

I suspect I have owned 15 or 20 various V8 Fords in my 80 years. And have been supplying plugs for the last 25 yrs. Ford always supplied plugs too cold for operation in Indiana. In the mountains it may be different." Don M.