Modern Gasoline Pros / Cons

[stevekleincustom]

For the benefit of many new AMCA Members and those who are in the process of a restoration project how about a "New Thread" on gasoline. Topics of interest could be:

- Modern formulations vs Old Formulations

- What modern gas has that vintage machines do not need and/or what modern gas does not have that Vintage Machines need.

- Octane levels and additives - Myth and Reality

Please offer insight and specify what period or manufacturer engine pertains to your example for clarity by our members.

Thank you to all AMCA Members for their passion for our sport, integrity and ability to share

Steve Klein

[jww]

Steve,
I think you and I are the only two members who are not in Eustis !
I'm sure the forum's activity will increase after the event.

[stevekleincustom]

I agree...Could not make schedule work here for Eustis....Klein

[yhprum]

I would like to understand if current normal octane would make to run hotter in a early machine.

My 1926 HD has a compression ratio of 3.7!! I have pondered actually lowering the octane of the gasoline/petrol by adding kerosine to the fuel.

My hypothesis is that the fuel may still be burning when the exhaust valve opens. Would lowering the octane speed up the combustion process?

I read in an old textbook that the octane availble back then was about 40.

Does anyone have any experience with this?

Thanks
Steve

[rickeieio]

Didn't Cotten do a comparison on gasolines about a year ago? Seems to me it might be good place to start this discussion.....

[Kojack]

I would like to understand if current normal octane would make to run hotter in a early machine.

My 1926 HD has a compression ratio of 3.7!! I have pondered actually lowering the octane of the gasoline/petrol by adding kerosine to the fuel.

My hypothesis is that the fuel may still be burning when the exhaust valve opens. Would lowering the octane speed up the combustion process?

I read in an old textbook that the octane availble back then was about 40.

Does anyone have any experience with this?

Thanks
Steve

I don't think high octane fuels have much to do with combustion temps. Octane is more of a rating system that describes resistence to igniton. A high octane fuel is harder to light off but burns pretty much the same afterwards, likely even a bit more evenly. Heavy fuels like diesel and kerosene are less volatile and slower burning and it seems they would be more likely to still be burning when the exhaust valve opens, as in your scenario. Your question has me wondering though. Heavy fuels have more energy in them than light fuels like gasoline. I wonder if cutting the gas with kerosene would allow the engine to produce a little more power. In a high compression engine it wouldn't be possible due to pre-ignition problems but the Harley motor sounds like it would tolerate it. I dug up an article on line that does a pretty good job of describing the different fuels:
http://www.prime-mover.org/Engines/G...es/octane.html

[Jerry Hatfield]

High octane fuel burns more evenly than low octane fuel. In other words, high octane fuel is less likely to produce pre-ignition. Pre-ignition is the combustion-chamber phenomenon of the advancing flame front and its pressure-spike causing diesel-like mini-combustions ahead of the main-combustion flame-front. All of this verbiage means, loosely, that low-octane fuel sometimes burns too fast.

In tuning for relatively short high-speed runs at Bonneville and other such courses, maximum performance is achieved when engine combustion is happening as fast as possible with the caveat "but without pre-ignition (loosely, without "knocking"). This is a big caveat.

In WWII, with aircraft reciprocating engines, for takeoff with unusually high gross weight and/or short runway, water injection was a vital technique. Prolonged end-of-the-runway wide-open throttle running, with the aircraft held motionless by brake pressure, produced a drop in maximum engine rpm as pre-ignition began to occur. The pilot then injected water in the amount and duration that produced higher rpm than had been achieved prior to the onset of pre-ignition. When the pilot saw the rpm reach this "super level," he released the brakes and the aircraft started its takeoff roll. The water injection was a temperature control technique, which allowed the engine to run as hot as it possibly could without pre-ignition.

Roland "Rollie" Free spent over 40 years tuning Indians and Vincents for maximum speed runs. He had a much simpler technique that would sometimes get an engine to run as hot as possible but without pre-ignition. He used the lowest octane fuel that wouldn't pre-ignite. The highly tuned Vincent Black Lightning would have little to no safety margin that would permit using lower-octane fuel. On the other hand, with a standard road model motorcycle, such as the Vincent Black Shadow, there was usually some margin of safety with respect to compression ration and ignition timing. Rollie Free asserted that a standard road-model motorcycle would usually run faster using "regular" gas than "high test" gas. This not only worked, but had the bonus value of the disingenuous rider being able to brag "...and I clocked this impressive speed even though I used 'regular' gas!"

[elt]

elt

Hi
New gas does not run in the old carb engines like the old stuff.I like useing aviation fuel myself it acts more like the old stuff and never goes stale .Add a touch of marvel mistry oil for the flat heads or any engine that sits for long periods read the lable on your air tool oil you will see its marvel.Over 40 some years of maintaining aircraft I found out that engines parked with marvel in them always passed the compression ck when removed from storage.As far as the water alchol caled ADI (anti detonate injection) and was used in the prop thansport planes and the first jets has little bearing on our old bikes.But used in the aircraft it gave a power boost on takeoff without overstressing the cylinders because of the cooling effect.When in the airforce in the late 50s I ran the old 115/145 purple gas in my model 50 Cushman scooter on the flight line for a period of years.It was airforce policy to let us use their gas to run our scooters while serviceing their planes.This gas was 115 octaine with a anti knock of 145.It never hurt my cushman.I have a Whizzer that I only use 100 lowled in wich is the only aviation fuel you can buy now.It usally does not leave the shead unless it is going on a 30 to 50 mile run.It can sit for a year and always fires up and runs smoth the first try.I use a ounce per gallon of marvel in it.For a biger flathead try 6oz per 10 gallon ratio.I am also a fan of aviation oil.Am running Aeroshell 15/50 in my beamer R90/6 have used it in my 48 cheif but hesitate puting in the 58FLH after hearing the argument that it is to slick for the crank rollers.It is said that they tend to slide rather then roll.But the Aeroshell 100 (50 weight) or 120 (60 weight is just fine) I know of a 41FL with 400K on one overhaul of the bottomend using it.So far the FAA will not let the EPA mess with the antiwear additives and as I get it they are trying to remove them from autommotive oil.
So as far as I am concerned you cant beat aircraft fuel and oil in your prised antique bike.Yes it cost a little more but like my late father told me son gas and oil is the cheapest thing you can put it in your engine.Hey the stuff runs great with it.
Enjoy
elt

[Baytown]

Real world fuel issues i.e 47 Chief

Ok fellas, so for the real world, let's say, in my 47 Chief, is 98RON fuel going to cause any issues?
I have the option here in Australia of the following fuels:
98 RON
95 RON
91 RON
E10 Ethanol blend (which I avoid like the plague)
Diesel (not really advisable!)

I would tend to go with the 98 RON after Jerry's post and the attached document dealing with Octane and Pre ignition / Pinging etc.
Any comments?

Best wishes all.

Ken.

[darrylri]

Keep in mind that the RON numbers from Australia (and Europe) are NOT what we see on the pumps here in the US. Subtract ~5 points from RON to get the US standard R+M/2.

So,
98 RON ~= 93 R+M/2
95 ~= 90
91 ~= 86

E10 should still have an octane rating associated with it. All gas sold in California is at least E10 (+ more stuff and - more gasoline), and you can get it in 87 - 91 octane ratings (that I've seen).

[Baytown]

RON etc

Hi Darryl.
So do you have a high octane fuel readily available from the pumps? I've been to the US numerous times, but now you mention it, I don't remember your pump ratings. Rental cars = cheep fuel anyway!
Best wishes mate.

Ken

[T. Cotten]

Let me try to simplify Mr. Hatfield's anecdote about Rollie Free's use of low octanes for Flatties:

Flatheads burn at a high optimum temperature: Lower octane fuels work well.
On the other hand, OHV's need higher octane fuels to burn at a lower optimum for their design.

If you put high octane fuel in a low octane machine, it just goes out the pipe.
Too high of octane fuel can actually inhibit the machine from reaching its optimum.


....Cotten

[darrylri]

Hi Darryl.
So do you have a high octane fuel readily available from the pumps? I've been to the US numerous times, but now you mention it, I don't remember your pump ratings. Rental cars = cheep fuel anyway!
Best wishes mate.

Ken

Short answer: no.

I guess there are a very few gas stations that, for whatever reason, know that they have the client base to keep something close to 100 octane* gas in stock. I've heard such stories but never seen one myself. Typical numbers here are 85-87 for regular and 91-93 for premium.

Then there are the folks who get some 100 octane low lead fuel at an airport. I have read that the Fed and State officials will be very harsh on whoever sells or gives them that gas should it be discovered, because no road taxes have been paid on it.

*) RON means Research Octane Number. The "Research" number is determined by a formula. There's also a Motor Octane Number, which is determined by running the gasoline in a particular test motor. Typically, there are 10 points between these numbers. In the US, the pumps are labelled with the average of Research and Motor numbers (eg, "R+M/2"), and so those numbers are typically ~5 points lower than the RON numbers.

[T. Cotten]

Other than Octane rating....

Other than octane rating, which really is only critical to those of us whose OHVs have elevated compression ratios, the major concern with modern fuels to the vintage motorcyclist is the digestive nature of additives.

Ethanol is corrosive by nature of its affinity to water. But carbon deposit inhibitors that have become associated with USA ethanol blends drastically shorten the lifespan of rubbers and other soft parts. Tank sealers can fail, original cork and composite floats log or swell, and if the noxious fuel spills upon a footboard mat, it can wrinkle forever. Even seasoned powdercoating can fall prey to the alien spit in P4gas.

We can only wonder what health hazards remain to be discovered.

....Cotten

[Baytown]

Ok, so Regular Unleaded is fine in my 47 Chief.

Flatheads burn at a high optimum temperature: Lower octane fuels work well.
On the other hand, OHV's need higher octane fuels to burn at a lower optimum for their design.
If you put high octane fuel in a low octane machine, it just goes out the pipe.
Too high of octane fuel can actually inhibit the machine from reaching its optimum.
....Cotten

Thanks for the sage advice Terry. I appreciate it. Accordingly, I'll go with the lesser rated fuel from now on then. My main issue with using the higher RON / MON fuel were the claims of a cleaner combustion chamber and carbie. These are a big marketing point down here from the fuel companies, and after seeing how much carbon my Chief can form, I wanted to keep the heads as clean as possible.
Congratulations on getting over the storm damage re your business. I have been going to get PEEK inserts for my intake manifold on the Chief since you released the service!
Best wishes from Oz.

Ken.