Gas options

['35Coup]

Hey All,
I mentioned this in another thread but I figure I’ll start a new one to get a larger response. What are your recommendations on gas? Specifically, what octanes to use with these old motors and what you are using for a leaded fuel substitute? I have obviously heard of the lead additives for regular gas but I have had a few guys tell me not to use those as they foul up the valves over time. I’ve also heard of putting a cap full of motor oil into every 5 gallons or so of regular gas. Thoughts?

[Old Henry]

I used to sucker for the myth that higher octane was better fuel, hotter, and more powerful. But, all of my research indicates otherwise. Octane rating (aka AKI or Anti-Knock Index) is nothing more than the fuel's volatility, i.e. how much pressure it can take before exploding. The higher the octane, the more pressure it can take. That's it. Nothing more. So, high octane is only needed in high compression engines like those modified for racing or modern engines. I was just studying new cars and discovered that, although the Smart for 2 has the highest gas mileage of any non-hybrid non-diesel engine, it gains such by its compression and, thus, requires high octane premium gasoline thereby reducing its true economy.

Anyway, because the stock flathead engines are very far from high compression engines, they do not need any higher octane than the very lowest that can be found at each elevation. (Octane is adjusted for altitude. Lower elevations require higher octane because of higher atmospheric pressure and, consequently, higher compression. I can buy lower octane gas [85] at the elevation that I live - 4,800 feet, than you who live near sea level. You can get higher octane than I can get up here because you need it down there.)

So, that's why I buy the lowest octane I can find at any elevation that I drive. To pay more for higher octane is a waste of money. To learn more about octane read here: http://en.wikipedia.org/wiki/Octane_rating
and here: http://mn.gov/commerce/weights-and-m...ctaneFacts.pdf
Here are all of the octane myths busted: http://www.google.com/#hl=en&sclient...w=1292&bih=890

l mentioned before CD2 Lead Substitute available on ebay as what I use. One ounce treats 10 gallons. So, 32 oz. treats 320 gallons and is for sale on ebay right now for $28.00 (here: http://www.ebay.com/itm/CD-2-Lead-Su...9f18e8&vxp=mtr). That's $.87 per once to treat 10 gallons or $.08 per treated gallon of gas. In comparison, other lead additives that you can buy at the auto parts store or gas station such as Red Line or Gunk cost about $9.00 to treat 20 gallons of gas. That's $.45 per treated gallon compared to $.08 for the CD2.

My 2 cents.

[Old Henry]

Originally Posted by '35Coup

a few guys tell me not to use [lead additive] as they foul up the valves over time.

Not likely. Lead used to be added to gasoline when our cars were made for two purposes: 1. It increased the effective octane of the fuel for less than the more expensive refining. 2. It facilitated heat transfer from the valves to the head to prevent valves burning. So, rather than damage the valves, it helps cool them to prevent burning. Modern engines do not use lead for two reasons: 1. They have harder valves that won't burn without the lead. 2. They have catalytic converters that are damaged by lead. Read more here: http://www.know-yourcar.com/Leaded-a...-Gasoline.html

[Vic Piano]

In everything I've read relating to early Flatheads and the recommended fuel, as I understand it, Ford recommended Amoco "white gas" (the equivalent of unleaded) be used... I've always run unleaded gas in our Flatheads, never put lead additive in but I do use MMO in the gas.

[G.M.]

I have used nothing but Marvel Mystery Oil since I restored my 39 years ago and it still runs good and is quiet after 110,000 miles. If I don't put the MMO in after 2 tanks of gas the valves stick.You can tell if the valves stick by dropping to 8 or 10 MPH in high gear and pulling out. If it bucks a little and everything else is OK it's the valves sticking from this new gas. Put a pint of MMO in the tank and after 10 miles try the test again and it should pull out smoothly. I don't want to have to hunt for a gas station, I want to stop at any gas station and buy gas. G.M

[Cecil/WV]

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I have always bought the cheapest gas I can find.

[Old Henry]

Originally Posted by Cecil/WV

I have always bought the cheapest gas I can find.

I agree. Even the cheapest lowest octane gasoline is still way better than anything available when our cars were made.

[rick r]

been using regular unleaded in my warmed over 8ba for the last 60,000 miles. no additives, no problems. our regular unleaded contains some ethenol.(usaually up to about 10%.

[mrtexas]

Originally Posted by Old Henry

But, all of my research indicates otherwise. Octane rating (aka AKI or Anti-Knock Index) is nothing more than the fuel's volatility, i.e. how much pressure it can take before exploding.

Another way of putting it is octane rating is that quality of gasoline that is resistance to ignition. The higher the octane, the more resistance to ignition. In other words you want the gasoline to ignite by spark and not by pressure.

Higher octane gasoline components tend to be slightly denser aromatics so you may be getting slightly more pounds per gallon.

On the other hand cetane rating for diesel engines is that quality of diesel that is how easily it ignites. With a diesel engine the fuel should ignite easily by pressure.

Back in the 30s gasoline was much lower octane than today. Gasoline consisted of the gasoline and naphtha cuts from crude which run around 70 octane. Some low octane thermally cracked gasoline was blended as well.

The really high octanes came when alkylation was invented in WW2 for aviation gasoline. Alkylation produces iso-octane. BTW 100 octane is defined as the resistance to ignition of 100% iso-octane. 0 octane is defined as the resistance to ignition of n-heptane.

After WW2 catalytic reformers was invented also know as platforming using platinum catalysts. Reforming produces benzene, toluene, and xylenes which are high octane from low octane naphthas. Remember the old Chevron TV ads that said "our gasoline has Platformate?" All gasoline has some platformate now!

One reason Fords had such low compression ratios was the low octane gasoline that was available. The higher the compression ratio, the higher the octane requirement.

I retired as a chemical engineer in an ExxonMobil refinery that made around 10 million gallons a day of gasoline. I've never bought anything other than 87 regular unleaded for any car I've owned. My 63 Corvette 327 runs fine on the stuff. So few cars actually require Super. Super is marketed to make the oil companies extra money and is not actually needed by most people. It used to be that the cost of manufacture for super was only 6 cents above unleaded but sold for 20+ cents more.

It used to be that regular unleaded had some thermally unstable components(color yellow or green) in it but not anymore. Virtually all gasoline now is hydrotreated to reduce sulfur to very low levels. The hydrotreating also fixes the unstable components. All gasoline now is "white" like Amoco used to advertise.

Remember in the 60s you used to here about 100 octane gas? That was research octane. Today octanes are reported as road octane. 100 octane of the 60s is equivalent today to Super which is about 98 research octane or 93 road octane.

[Old Henry]

mrtexas, I was hoping you'd chime in here 'cause I know you know more about gasoline than most of us combined. I'm sure your refinery chemestry jargon and lingo is way over some of our heads but your bottom line was the same as mine - no need for anything other than the lowest octane for our stock flathead engines. At my elevation that's 85. I guess at yours it must be 87. Either of those is still higher than the 70 our engines were designed to run on.

[mrtexas]

Originally Posted by Old Henry

mrtexas, I was hoping you'd chime in here 'cause I know you know more about gasoline than most of us combined. I'm sure your refinery chemestry jargon and lingo is way over some of our heads but your bottom line was the same as mine - no need for anything other than the lowest octane for our stock flathead engines. At my elevation that's 85. I guess at yours it must be 87. Either of those is still higher than the 70 our engines were designed to run on.

The octane requirements for engines goes down by about 1 octane per 1,000 feet of elevation

[Marvin/TN]

I used to use a little 115/145 avatian gasoctane in my VW when I was over in Germany not often just once in a while.

[Uncle Bob]

A small correction on the octane rating system nomenclatures. The two methods done on lab engines that establish the values stated are Research (R) and Motor (M). The Motor method uses more severe test conditions so produces a lower number than the Research method. In over simplified terms, Research is for mild operating conditions, Motor for more severe. Anti-knock Index (AKI) is an invention resulting from government mandate and is calculated by averaging the scores a fuel gets in the testing which results in the number you see on the pump. If you look at the label on the pump many times in smaller print below it will show the formula R+M/2=AKI

[rotorwrench]

When I was a kid, we used to get casing head gas or drip gas from the natural gas pipelines in the area of the Hugoton gas field in southwestern Kansas. The stuff is basically condense from the natural gas coming out of the ground. I have several friends that work in the industry so it was easy to get and free for the taking at the time ( it ain't no more). It was probably equivalent to 67 octane but the old 51 Merc ran just fine on the stuff.

When I first started working in aviation, there were still a lot of little Cessnas and Pipers that ran the old C-65 through C-145 Continental engines. You had to run Marvel Mystery Oil in the little ones or you would for sure stick a valve at some time or another (not too fun on take off). With the MMO, I never heard of any sticking a valve. Running the 100LL avgas in them is way overkill for octane. They ran better on 80/87 with their low compression. The Hughes/Schweizer 269C helicopters I work on are 190 HP HIO-360 types with 10:1 CR fuel injected and they have to have a minimum of the 100LL or they won't run well at all. Compression ratio and piston/valve size are the biggest factor for octane requirements. You can manually lean the mixture at altitude so it's not a real big factor.

Auto fuels are blended for the temperature and conditions of the place thay are to be sold. When I lived up in Colorado, you could have vapor lock problems if you purchased winter blend fuel during a warm up in late winter or early spring times. The vapor pressure level was lower for the cold weather fuel.