FUEL: Regular Unleaded VS Hi-Octane

timeconsuming

timeconsuming

Foolish until proven intelligent.
Hey guys

Not sure if this topic has been covered, feel free to link me up if so!

Anyway I was hoping to gather some opinions on fuel in vintage bikes. I have always run hi-octane (I think 91?) as I figure over the course of a year it's not that much more out of my pockets (+.20 per gallon over regular unleaded on average) and it should help to some extent, right?

Unnecessary?

In-line filters regardless? Let me hear it!
 
Running a stock motor? If so, high octane gas is a waste of money and actually giving LESS performance than low octane gas.
 
I'm running UNI pods, rejetted carbs and aftermarket (MAC 4-1) exhaust on a 75 cb400f.

It's my first bike and the guy I bought it from back in October swore by hi-octane fuel so I just took his advice.
 
Yes, your motor is "stock".

Higher octane gas doesn't actually provide more energy. It is for high compression motors that will detonate on lower octane gas. Feel free to do some Google searches for more info.
 
Yup. High octane fuel lets you run a bit more advance and/or a bit more compression without bad things™ happening.
 
Curious if the high octane not completely combusting in the engine might attribute to any additional decel popping?
 
High Octane in Australia is 98. It is all I use. I know I don't need it but I would rather have the better stuff. Why drink 1 year old scotch when you can have 18yo.
 
Big Rich said:
... It is for high compression motors that will detonate on lower octane gas.
Click to expand...
This ^ is the answer. It all depends on the compression ratio of your engine.
Now, with that said, my old CB350Four in stock trim called for Premium fuel in the owners manual.
 
I have run both in my cb450k. I think that my bike runs smoother and has better throttle response on the the "good stuff". Try to run ethanol free gas if you can find it in your area. That is truly better for your bike.
 
If you run a motor on the dyno, you will fiund that if it doesn't "need" high octane gas to prevent detonation, it will make more power and run smoother on lower octane fuel. High octane fuel does not make more power than low octane fuel per se.

The 400F isn't a bad combustion chamber shape, so it is quite possible that it could run fine on less than premium.

The question is what does your engine need. What does the manual say? I'd start there.
 
Anyone know at what compression ratio premium becomes more helpful than
hurtful?
 
The compression ratio for premium is not fixed. timing advance, combustion chamber shape also have an big effect. Also, if your combustion chamber is carbonized, you can get pre-ignition from hot areas of carbon. As you get above 10:1 the need for higher octane is more common.

The other confusion that arises is that in the 1960's to early 70's, the octane advertised at the pump was the higher of 2 numbers. In the Seventies, congress came out with a law to advertise a new number, a combination of the first 2. There is RON, MON, and PON. Research Octane Number (RON) is a chemically calculated number. It is a High number. Motor Octane Number is derived from an adjustable motor, and the numbers are lower. Congress created Pump Octane Number (PON) that is (RON + MON)/2.

What this means...My CB360 Manual calls for 91 Octane (RON) or 86 Octane (PON). Everything sold in the US today is PON. I can't find anything lower than 87 PON in the northeast. Some higher elevations out west do have 86 PON. On a properly running, stock CB360 (350 is the same, as is most of the 60's-70's bikes), anything over 87 PON is a waste of money and offers no improvements in running or fuel mileage. Since vapor pressure on higher octanes is lower, you may find slightly harder starting when cold.

Ethanol additives cause leaner running, but ethanol is an octane rating raiser.

If you aren't pinging or have engine knock with regular 87 PON, don't waste any money or time with a higher rating.

There are older bikes that need high test.If your old manual calls for 100 Octane (RON) then you need the 91 PON....

Confusing, but the newer numbers are more accurate then the older number.
 
Teaze has it right I'll only add that the higher octane fuels are slower burning thereby requiring "cleaner" combustion chamber shapes and additional ignition advance for complete combustion . It is conceivable that stock tune up specs and a 8.5:1 compression ratio would be allowing more unburned hydrocarbons into the exhaust than a relatively lower octane fuel . The popping on deceleration is a combination fof factors starting with throttle opening vs ignition advance at idle and ending at idle mixture . a combination of applying as much ignition advance as is prudent at idle and an increase in pilot discharge should decrease or eliminate the popping .

~kop
 
By far the most intelligent responses of any forum I've ever had the pleasure of posting in. Thanks gentlemen!

My Clymer book says this:

3.7 US gal. (14 liters) total - 86 octane (pump)
0.8 US gal. (3 liters) reserve - 91 octane (research)

Anyone care to enlighten me as to what this is specifying ?

I take it I can run regular unleaded, and plan to test things out this week, but what is this 3 liter reserve/research listed under 91 octane ?
 
timeconsuming said:
By far the most intelligent responses of any forum I've ever had the pleasure of posting in. Thanks gentlemen!

My Clymer book says this:

3.7 US gal. (14 liters) total - 86 octane (pump)
0.8 US gal. (3 liters) reserve - 91 octane (research)

Anyone care to enlighten me as to what this is specifying ?

I take it I can run regular unleaded, and plan to test things out this week, but what is this 3 liter reserve/research listed under 91 octane ?
Click to expand...

Just poor editing 86 PON = 91 RON

They just didn't format it well...
 
I am lucky enough to be surrounded by a lot of rich farmers. Who have lots of antique tractors they like to show in parades and such. They insist, Don, down at Dons Marathon stock this stuff. 90 octane recreational fuel. Its pure gas, no ethanol or alcohol. Means its easier on any carbureted engine. lawn mowers, chainsaws, snowthrowers, VINTAGE MOTORCYCLES. It wont dry out o-rings and diaphragms. Don tells me, Most gas starts out as this 90, then they either cut it or boost it w ethanol/alcohol additives to get 87 or 93. It cost the same as the 93 in the pump next to it.
So, you may call around or whatever to different stations, somebody close to you may stock it.

gas_zpscf120d3d.jpg
 
SONICJK said:
Anyone know at what compression ratio premium becomes more helpful than
hurtful?
Click to expand...

That's a really good question and as Mid Life mentioned there are many factors including combustion chamber geometry, ignition advance, hot spots, lean mixtures and so on. One are that really hurts many bikes is those with a fat squish band that traps hot gas which then detonates. Many 2 strokes were like that. Making the squish band thinner helps to eject those gases to speed up flame propagation and it reduces the risk of detonation. A GT750 Suzuki for example has a bout a 2mm gap and badly oversized head gasket and they often detonate the head gaskets out and blow holes in pistons if they are tweaked at all.
 
trek97 said:
I am lucky enough to be surrounded by a lot of rich farmers. Who have lots of antique tractors they like to show in parades and such. They insist, Don, down at Dons Marathon stock this stuff. 90 octane recreational fuel. Its pure gas, no ethanol or alcohol. Means its easier on any carbureted engine. lawn mowers, chainsaws, snowthrowers, VINTAGE MOTORCYCLES. It wont dry out o-rings and diaphragms. Don tells me, Most gas starts out as this 90, then they either cut it or boost it w ethanol/alcohol additives to get 87 or 93. It cost the same as the 93 in the pump next to it.
So, you may call around or whatever to different stations, somebody close to you may stock it.

gas_zpscf120d3d.jpg
Click to expand...

See Here: http://chemistry.about.com/cs/howthingswork/a/aa070401a.htm

Straight gasoline has an octane rating of about 70. Additives are what are used to bring it up. Ethanol, is an octane booster, btw.
Remember, octane is only resistance to ignition. The higher the octane, the more resistant to igniting. when said that way, it doesn't sound as good, does it?

The chemicals and additives are used to not only bring octane up, but also have detergents and preservatives to keep the volatile components from evaporating too fast. "Pure" gasoline is not usable at all in any engine.

As we know, ethanol is corrosive, so it is not good. Lead is not good for humans, so that is no longer used. But there are many different additive needed to make a 90 octane gas, so the only purity the rec. gas has is that there is no ethanol. that isn't a bad thing.

Except that ethanol is corrosive to many rubber and metal parts, it is not good or evil. Ethanol has less BTU per pound then gasoline, so mileage is less because more ethanol blend is needed to go the mile then non-ethanol gas.

The right answer, use the lowest octane rating gas than doesn't knock or ping for the best results. Your owners manual has the Octane rating that will be known to work. Extra Octane ratings do not increase power, do not run cleaner, and you go a little faster with higher octane because your wallet is a little lighter.
 
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