aJ baimes "arsenal of democracy"

[Daniel828]

I just finished listening to this book on audible it was very good but it focuses on Edsel a little more than Henry. Anyway, the book mentioned that two types of fuel were supplied in the willow run factory, 78 octane for the trucks that were used on the factory grounds and 100 octane for the bombers engines. My question is, do lower compression engines run better on lower octane fuel? or doesn't it matter? ive never even heard of 78 octane
fuel

[Bill Dizer]

Octane is the rating of the fuels ability to resist spark knock, the higher the rating, the more resistant it is to knock or"pinging". The higher the compression is, the higher the chance of spark knock, turbo charging or supercharging also increases the knock chances. Some aircraft and even pt boat engines used up to forty inches of boost, and ran up to 140 octane fuel. The additives used to prevent the knock often didn't run well in low compression, or un boosted engines. In some cases they used a water/alcohol mixture sprayed in the intake/carb to keep the knock down. They still do at the Reno air races! Pinging is when the fuel is ingnited by a hot spot in the combustion area, other than the spark plug. The flame fronts meet and cause the ping, because it usually ignites at a different time in the power stroke than the correct plug timing. It can be very destructive to pistons, valves, heads, and blocks, causing anything from pitting to total failure of the parts. The aircraft fuel used different colors to tell the octane rating.

[RustyFords]

One of the neat things I see on a regular basis is the "knock engine room" at the big Valero refinery in Houston.

I'm oversimplifying but essentially it's an internal combustion engine with a head that can be raised or lowered thereby changing the size of the combustion chamber and the compression ratio of the engine.

They run a reference fuel in it to calibrate it, then they run their gasoline through it to verify the octane rating. It's called a knock engine, because back in the day, they'd wait to physically listen for a knock. These days it's a bit more elegant than that, but it's the same principle at work.

New, from Waukesha, these engines cost in excess of $500,000. The reference fuel is roughly $2,000 per barrel and the technicians who babysit the machines make a very decent salary. Per ASTM methods/rules, the engines have to be mounted on a specifically designed concrete pedestal and must be stripped down regularly and examined and certified.

All to get that little octane rating number that you see on the gas pump!

[GrandpaFord]

What Bill said about the additives to boost the octane rating is true, but I don't think the high octane gasoline available at gas stations will make any difference to how a normal Model T will run.

[Norman Kling]

I don't think a high octane gas will hurt the T engine, however, it is a wast of money because it costs more. The compression on a stock Model T engine is not enough to cause the normal low octane gas to knock unless the engine is severely overheated. In fact, a ping is a good indicator that your engine is overheating and that you should let it cool off.
Norm

[John Codman]

Bildizer pretty much nailed it. The problem with high-octane rated gasoline in low-compression engines was that for decades, octane was raised with the addition of tetra-ethyl lead. The really high-octane avgas was the purple stuff and it contained gobs of lead. The lead in amounts greater then a particular engine required often resulted in lead-fouling of spark plugs and other deposits due to incomplete combustion. Lead is no longer used in auto fuel in the USA; Octane is boosted by other chemicals that do not leave significant deposits. The use of high-octane auto fuel (93 Octane usually) will gain you nothing but a lighter wallet in a car that doesn't require it (think Model T), but it won't hurt anything.
To expand a bit on Bildizer's excellent comments, Detonation can be extremely destructive, most of us at one time or another have had a gasoline engine Diesel or "run on" after we shut off the ignition.This is caused by hot spots in the combustion chamber usually due to carbon, lead, or some other type of deposit. This is such a concern to aircraft engine manufacturers, that airplane engines are shut down by stopping the flow of fuel rather then the spark. No fuel = no possibility of running on.

[2nighthawks]

John Codman - Please forgive the slight "thread drift" here, but this has become a very interesting thread, and you and Bill D. have come pretty close to a couple "pet peeves" of mine. First of all, I use strictly non-ethanol gasoline in my Model A and four Model T's, because there are several qualities afforded by the non-ethanol gasoline that make it worth the extra expense, one of which is that it does not cause the Springtime hard-starting problems that I used to experience with a Model T left all winter with gasoline in the tank.

Also, correct me if I'm wrong (.....happens all the time ) but I'm of the opinion that the petroleum industry was able to discontinue the use of tetra-ethyl lead (sometimes called "anti-knock-compound") because the ethynol they add to modern gasoline has a tendency to raise octane and thus help to prevent "ping" or "knock" or pre-detonation or whatever you want to call it, as the tetra-ethyl lead used to do.

Another "pet peeve" of mine (....here comes the "thread drift",....sorry) is when the petroleum industry phased -out the term "ethyl",....as in,...."fill 'er up with ethyl" as we used to say, and introduced the term "premium" gasoline, which tends to make a lot of people think that using "PREMIUM" gasoline is doing a lot of "good" for their engine, even when it does not require anything more than the cheaper "regular" gasoline. I had a heck of a time trying to convince one of my sons that he was just wasting money in using "PREMIUM" gasoline in his cars that really didn't need it! Okey,....end of "rant",.....sorry,.....harold

[Daniel828]

Thanks for the replies everyone. What I think I failed to explain was, the T engine is what, 6:1 compression ratio ? So in regards to the way the engine sees 83 octane gasoline as premium 92 gas. I’m just spit balling here. I don’t mean for this to turn into what is the proper oil for model t engines.

[2nighthawks]

Daniel - Actually, a stock Model T is more like 4 to 1 compression. An accessory "high compression" head that's sometimes advertised to afford 6 to 1 is not really quite 6 to 1 compression,.....FWIW,.....harold

[Susanne]

I miss riding with my ol' friend Ethyl, but my modern cat sure doesn't like her... I remember some of those early lead substitutes caused some real havoc with plug fouling...

What I find strange is that my car actually does run smoother (and cooler) running higher octane fuel, this both from driving "feel" and observation of things like motometer position, exhaust sound, and stumbles... I would think that, being a low compression motor it wouldn't make a whit of difference, but it does. I was trying to figure out some scientific basis behind this phenomenon, but I eventually realized the car just likes to feel pampered... and when I run the cheapest stuff from the thrity pit gas station she lets me know.

[Oldav8tor]

Aircraft fuel available today is still leaded and set at 100 octane. My aircraft's engine was originally certified for 73 Octane but only 100 is available. The only issue I notice is a greater tendency towards lead fouling of spark plugs. No improvement in performance compared to when 80-87 octane was still available. Higher horsepower aircraft engines are higher compression and require 100 octane to avoid detonation, or so I've been taught.

[Daniel828]

Your right Harold, about the compression ratio. I have a Z head so I have 6 to 1 on my brain

[Bill Dizer]

Ethyl was actually a brand name that became so commonly used that it was used universally to describe higher octane fuel, regardless of brand. The lead was both an anti-knock agent and a valve lubricant combined, and was removed for environmental reasons beginning in the mid seventies, being replaced with unleaded gas. This was the same time catalytic converters began being installed on autos. Fuel management was so poor that converters didn't work well for long, and were often removed after they plugged up. Modern computer controlled fuel injection has pretty well cured that. Ethanol was introduced for multiple reasons, partly to help farmers sell corn, and it was heavily subsidized to the oil companies. Automakers found that it helped lower emissions because of increased oxygen in it, and it helps with spark knock because it burns cooler, lowering combustion temperature and hot spots that cause pinging or knock. It lets them advance the timing for power and performance. The major down side of ethanol is it is hydroscopic, meaning it mixes with water, even humidity in the air, which causes corrosion in fuel systems, especially older ones with pot metal, or aluminum parts. Another down side is that it has less BTU's than straight gasoline, and since BTU's are measures of heat energy that provide the power in gasoline, lower energy means lower gas mileage.
The only real reason to use modern premium gas in a model t is that some premium is made alcohol free in many parts of the country. That makes it popular for older outboards, mowers, chainsaws etc. that are made with corrosion prone parts. As far as aircraft are concerned, most of the older 80 octane engines can be certified to run unleaded auto gas, as long as it does not have alcohol in it. There used to be a product called TCP that you could add to the older 100 octane avgas to help prevent plug fouling issues. They have since lowered the lead amounts in the 100 octane avgas again so it lessened the issue some more.

[Susanne]

OK. Since there's so much disinformation around Tetraethyl lead... if I may...

"Ethyl" was a trademarked designator for the fuel additive Terraethyl lead. It was a trademark of the Tetraethyl Lead Corporation.

Lead compounds poison Cat Converters. They react witht he palladium and platinum pellets, and cause them to be irrevokably coated, making that cat dead. The pellets draw these compounds tot hem, so not only do they kill the chemical reaction that makes Cats work, they clog Cats. THATS why there's no more lead in fuel. Otherwise - it was an elegant solution to slow down the uncontrolled combustion of the lower distillates of fractured hydrocarbons they sell as "gasoline".

They tried numerous compounds to raise octane when they realized lead could be no more, so tey tried numerous compouns to replace it - Methyl tert-butyl ether was the next great thing, but not only did it not prevent plug fouling (remember the red stained porcelains?) but ended up more poisonous that TEL ever thought it would be.

The result they came up with was Ethanol blends. It slows down the combustion of (cruddy) Gasoline to keep knocking somewhat down. Problem is... ethanol. Bad for most of the vehicular systems. And if you have a LONG memory, you'll notice the aroma of what they're selling you as Gasoline smells nothing like what Gasoline used to smell like - more like paint thinner...

I've studies this stuff. Actually, being a "chemistry geek", I always wanted to find a safe, reliable sub for TEL, but while I'm a schmart Chick, I am not at the level of those who do this for a living and as such, well...

Unless gas is sold as Ethanol Free, it has Ethanol, as that's the Anti-Knock oxygenator in the fuel. The "alcohol free 93's" and whatnot resort to things like MTBE to punch the octane up, and it works, but if you look at your snowblower that you've run "ethanol free fuel" in, you'll see the characteristic staining of the other anti-knock compounds. Even "Premium" - actually, to get those Octane #s up, they need MORE Ethanol.

I actually have a source for 110 octane leaded fuel - but I break that down with ethanol free gas to about 90 octane. Since I no longer run 60's big blocks (at least for now), it's not as critical, but still... I also have a good source for Non-Ethanol 96 octane, but their "blender" uses MTBE, so I check (and clear the fouling on) my plugs judt like the good old days, plus I wear gloves now... because that really IS some nasty stuff.

[Susanne]

And yes, while there's no reason I can figure, my car does run better on higher octane fuels. Really wish it weren't true, and am ready to drop a high head on it so I can run cheap gas. But it is what it is, so I'll pamper my princess of a car...