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

_________________
http://www.youtube.com/hyperpack

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

_________________
一期一会
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.

_________________
http://www.youtube.com/hyperpack

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.

_________________
一期一会
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?

_________________
http://www.youtube.com/hyperpack

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.

_________________
一期一会
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

_________________
http://www.youtube.com/hyperpack

Interesting articles, but they all miss an important point or benefit to a higher octane fuel that is very beneficial in a naturally aspirated engine. Engine temperature is or can be effected also, due to the fuel quenching the combustion chamber and of pistons more efficiently.
When I was racing years ago, I would cut my pump gas (93) 25% with Cam II (110) and it would lower my engine temperature around 10 degrees less than running straight pump gas. This was with a 9.1 compression big block, iron heads, 2" primary headers, 109 LSA cam, etc. I've also experienced in some vehicles I've owned over the years, that it will effect mpg too, I've had a few small block Chryslers actually go from 12-13 mpg to 16-17 mpg with 89 vs 87.......back in the 80's with the prices of fuel then it was actually cheaper to run 89 instead of 87. Yet, my 2019 3.6L in my Promaster van had absolutely no change in mileage going from 87, 89 or 93.
So, engine design in my opinion does make a difference.

Back in the '70's we hung around a "Gulf" gas station, and had a similar discussion. We did an experiment. I don't remember the vehicle or engine specs, but we compared the "regular" to "no knox". With a "stock" type tuneup, we got better fuel milage with the regular. BUT running "No knox" and advancing the timing then we got the best milage. We could not run that much advance with the "regular" without pinging. I feel a better measurement is miles per dollar not miles per gallon. Particularly with these new(er) computer cars, that will adjust the timing depending on whether getting preignition.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

No, it really does not. This isn't a thing. Why isn't it a thing? Well, many reasons, starting with that is not even close to what "quench" means in context of an internal combustion engine.
We're talking about street engines driven on street gasoline in this thread.
The human memory isn't a camcorder, it just feels like one.
I don't say you couldn't have seen what you saw, but if you did, it wasn't for the the reason you describe. The explanation you've come up with is not grounded in reality. There is no difference in engine operating temperature depending on whether you pick Regular, Mid, or Premium at the gas station, or add Cam2 or any other brand of racing gasoline. There really just isn't. And that is why all those articles in those high-level publications, written by people who know this stuff for a living, do not include anything about it.
Nope. It won't because it can't; not in a car like the ones we discuss on this forum (and not even in a giant majority of cars new enough to have extensive computer control over every aspect of engine operation).

When what we think we see violates laws of physics and thermodynamics and other fundamental chunks of reality, either we're not seeing what we think we are, or we're not understanding what we're seeing, or our highly suggestible human mind is doin' its thing, or we're not remembering correctly.

I don't intend any personal attack on you; my squawk here is in re misinformation. Also, none of this will help the OP fix their plug-fouling problem—it's not because they used regular instead of premium or vice-versa.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I agree that the plug fouling will not be solved by different fuel (unless your fuel has been sitting for 10+ yrs) OR by changing plugs.

You have a fuel mixture problem, and maybe a timing problem too. The fact that you rebuilt the carb is the biggest thing to investigate. Try another known good carb, or try adjusting the carb you have or looking for damage or air leaks. We all make mistakes or buy faulty kits/parts from time to time. I have ruined or misadjusted plenty of carbs myself over the last 40 years.

I am interested in the higher octane resistance to burn vs. longer burning idea. Thank you for the links and writing, Dan. This is new thinking for me, but it makes sense. For one thing, we might expect that if the fuel is more highly refined, then the variation (spread or distribution) of gasoline molecules/sizes will be smaller, and thus the ability to preignite will be lower. Lower octane rating fuel might have a wider range of molecule types, so some of the smaller (or differently shaped) molecules will preignite more easily and start all the other ones burning, causing knock. There are many factors to describe fuel quality, and octane number is just one. Energy density would be another critical one.

I would like to caution readers here that Dan is trying to convey information, and he is upset about the misinformation propagated on the internet and around the campfire. I recommend that people on this forum should NOT read Dan's comments as attacks on you, but his "stern" (haha) criticisms of how generally we as car people (or just flawed people in general) are trained to talk about and think about information.

Maybe we should start another thread about octane and preignition and fuel?

Thanks for reading,
Lou

_________________
Home of Slant6-powered fun machines since 1988

Question for ssd...locally the only way to get fuel that is NOT 10% or more ethanol is to buy premium from one or two stations in town. Do you believe there is an advantage to pure gasoline for a slant compared to a "gasohol" blend.

I know the small engine stuff (2 stroke trimmer/saw/blowers and lawnmowers) much prefer real gasoline. Not as corrosive and not as finicky in storage.

Probably not. Ethanol contains about 30 per cent less energy per unit volume (gallon, litre, whatever) than gasoline, so E10, which is 90 per cent gasoline and 10 per cent ethanol, contains about 3 per cent less energy per unit volume. That means you lose that same amount of fuel economy, about 3 per cent—which is very close to what was found by experiment in this Project Farm video (he found 4 per cent, but wasn't using precision measurement, testing, or timing techniques and did only one run with plain and one with E10, so I'm counting his 4 per cent as confirmation of the 3 per cent). He also found no significant difference in combustion chamber or spark plug fouling.

So if the price of non-ethanol gasoline is more than 3 per cent higher than the price of ethanol gasoline, the non-ethanol gasoline isn't economically worth buying. Given that non-ethanol is a high-octane gasoline, I'm guessing it costs what, 30 or 35 cents more per gallon than E10 regular. Going by the current US national average gas prices, as I write this high-test is $4.164, which is over 24 per cent higher than regular ($3.351), so the math doesn't work out in favour of buying the non-ethanol.

There is the matter of fuel system materials compatibility/corrosion, which—yes—is a significant issue particularly in small engines that sit for long periods of time in the garages and sheds of owners who don't bother to drain the fuel before storage like they're supposed to. Yeah, that's gonna cause problems, aggravated by the cheapest-possible nature of many small engines and their carburetors. To be entirely fair, let's remember that back in the old days, when alcohol was considered a contaminant in gasoline, leaving gasoline in any kind of engine for months on end caused big problems with varnish, gum, and other corruption.

Ethanol can cause problems in some old cars ("remanufactured" carburetors that have been abrasive-cleaned and not repassivated, so the raw metal is exposed), and maybe even in good carbs that sit for months and months on end, but my sense is that the oil companies have got better at blending—better cosolvent additives, etc—so there's less risk of the alcohol separating out. Plus, ethanol has been in the fuel supply for long enough that the big wave of problems caused by it freeing up gum and crud in the system and clogging fuel filters, etc, crested and passed long ago. About the only other outstanding matter is rubber fuel hoses (sender to hardline, hardline to pump, and either partially or completely pump to carb); fix this easily and permanently by rehosing with SAE J30R9 hose. Beyond that, as this other Project Farm vid shows, fuel stabilizer can probably adequately mitigate any problems one might run into with carbureted cars used at least semi-frequently.

(All that said, I still wanna know where's our hydrous-ethanol gasoline, dammit‽)

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.