Massive fouling issues here. Gonna run some NGK ZFR5N plugs as I've seen a few places it's a good plug upgrade. Car is a 68 Barracuda but the head is newer with 5/8 gm style plugs. Any information would be great

Changing plugs alone will not solve your fouling issues. You will just have fouled ZFR5N's

Please post good detailed pictures of your current plugs.

Could be fuel mixture/choke etc, or oil control (rings/valve guides or valve seals), or something else relating to heat range if you have modified camshaft or compression somehow.


Greg

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ZFR5N is a gasket-seat spark plug, not a taper-seat plug as used in '75-up heads.

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Too many people who were born on third base actually believe they've hit a triple.

I can post pictures of the plugs this weekend. They are black and dry. Engine has been rebuilt. Carb has also been rebuilt 2 months ago. I put new plugs in and they fouled pretty much instantly. Some on other forums said adjust floats which I did. Don't really think the floats were sticking as no fuel is coming out of the vent. Carb is a Holley 1920. I'm going to try the new NGKs as they will reach a little further into the head. Choke seems to be operating correctly but who knows when its going down the road. Running 93 no ethanol fuel. Engine fires right up so my timing is good. Did a valve lash job recently as well.

Try regular 87 fuel. 93 Has no business on a slant 6 if it is stock cam/compression. It will burn at a slower rate possibly causing issues.

If you have the "peanut head" the plugs you are asking about will not work anyway as they are gasket type and the peanut head is the tapered non gasket type plug.

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True. Not so. There is no benefit to running high-test gasoline in a stockish Slant-6, but there is also no drawback—except to the wallet. High-test doesn't burn slower, it more strongly resists spontaneous combustion (detonation, ping, knock…). 93-octane gasoline is wasting the OP's money, but not causing his spark plug fouling or his rotten running.

One doesn't follow from the other.

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Too many people who were born on third base actually believe they've hit a triple.

Great, thanks for clarifying.

How does that detonation resistance work out if it does not burn slower?

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I'm not a combustion expert. My understanding is that combustion is categorized as uncontrolled/spontaneous explosion (bad; this is preignition or detonation) or controlled/progressive burn (good; this is normal), and that resistance to the bad kind doesn't necessarily imply anything about the speed of the good kind. That is, a fuel doesn't have to have a relatively or absolutely slow burn in order to resist detonation.

Lookit (hit the sublinks).

And lookit (MIT School of Engineering): (…)Ideally, the vaporized gasoline inside an engine’s cylinder burns by the propagation of a wave of flame, ignited by the cylinder’s spark plug. This allows a smooth transfer of power to the engine’s crankshaft and the car’s wheels. But at higher pressures or temperatures, small pockets of gasoline vapor can prematurely explode, or self-ignite, creating a distinctive “knocking” sound, as well as potentially destructive shock waves. Gasoline with a higher octane rating does not self-ignite easily, and burns more evenly than lower-octane fuel under harsh conditions, resisting detonation and knocking.

And moar wordz about the unrelationship between octane rating and combustion speed, with apparently sturdy references.

And here's one from Scientific American, reinforcing the difference between knock and burn.

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Too many people who were born on third base actually believe they've hit a triple.

Thanks Dan! When I get some time, I will digest all of that.

Greg

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