Topic: Premium vs. Regular Gas?

[Jim Harris]

My buddies and I are having a debate and we need some guidance from the experts (that's you guys)! We all ride carbureted vintage Honda's and Yamaha's from the 70's. A couple of us run high octane premium gas in our bikes and other use regular gas. The premium guys can feel the difference in power using the high octane gas and think that it keeps the plugs cleaner. The regular gas guys feel that using premium raises the firing temperature above what the manufacturer intended. Other that costing more, has anyone seen any detrimental effects from running premium gas in 1970s bike engines?

[bjbuchanan]

It all depends on how the engines were designed from the factory. Compression ratio, ignition timing, how "smart" the carbs are, plug heat range. Little things add up in a big way

The biggest detriment with higher octane if unnecessary is to your wallet and you combustion chamber. It costs more and over time leaves deposits. The higher octane is resistance to detonation. If you don't need the higher resistance don't use it.

89 to 91 is around the sweet spot for the older bikes. 87 is alright for cold weather. that mid range fuel is more similar to the leaded stuff

[Goofaroo]

It all depends on how the engines were designed from the factory. Compression ratio, ignition timing, how "smart" the carbs are, plug heat range. Little things add up in a big way

The biggest detriment with higher octane if unnecessary is to your wallet and you combustion chamber. It costs more and over time leaves deposits. The higher octane is resistance to detonation. If you don't need the higher resistance don't use it.

89 to 91 is around the sweet spot for the older bikes. 87 is alright for cold weather. that mid range fuel is more similar to the leaded stuff

Yep.   The higher octane fuel is simply less volatile to reduce detonation on a high compression engine.  There certainly won't be any benefit unless you need it to keep the motor from pinging.

[750K]

I use 91-94 depending on which station I end up at, Shell or Chevron. Mainly due to their premium gas being ethanol free around here. I'm sure it would run just as nice on mid range but there's ethanol in all of them at the local pumps.

[FunJimmy]

I've heard (and I may be wrong) that high octane fuel packs a lower punch in engines that don't require it, due to a lower volatility. Slower flame propagation was the basis for such claims.

As mentioned already, 94 octane fuel in Canada is ethanol free and that could provide sufficient justification for the added cost. 

[BeSeeingYou]

This one has been going on for years.   The high octane gas has a higher ignition threshold for high compression engines where lower octane would pre-ignite under the higher pressure.  In an engine designed for lower octane running this gas can lead to carbon buildup from incomplete combustion.  Then when you do try and run lower octane the carbon deposits can pre-ignite the mixture.  So then you have to run high octane...all you have done is made an octane junkie out of your engine.  The proponets all claim they can feel the added power but it's all wishful thinking. We can convince ourselves of many things....all you have to do is believe.   I think you could do better by placing magnets on your fuel line.

[Jim Harris]

OK, so what I'm getting out of all of this is that regular is probably the right fuel for those mid-70s bikes, but the mid-range gas may offer some advantages, but the high test premium is actually doing harm unless your engine needs it to get rid of ping.
Thanks you gentlemen!

[Jerry Rxman Griffin aka MuthaF'er]

9:1 or 9.2:1 CR does not require premium. Some premium is advertised with additional cleansing additives. If that is the case then run an occasional tank of premium.

[dave500]

our octane numbers are different over here,we have 91,95 and premium 98,,the 91 mostly has ethanol and is reserved for peasants,some 95 may have ethanol and 98 mostly dosent,i just run our 95 non ethanol as ive had no sudden power gain from the 98 in my car or bike,you can soot up a little more if your running 98 in low compression older engines,i only get fuel from a good name station rather than those dodgy off brand ones the type of which have been exposed to have been selling 91 from the 98 pump etc,and watering down the 91 with even more ethanol.

[Jerry Rxman Griffin aka MuthaF'er]

There goes the Aussies showing off again    Dave, our 'regular' here in the Rocky Mountains region is 85 and the 'good' stuff is 91, all 10% ethanol. We'll be coming off the winter blend soon and fuel mileage seems to pick up 10% so I'm not sure about the differences.

[dave500]

our rating system is different,our 98 might be like your lesser octanes or something?you can shove that ethanol where it stings!

[Eydugstr]

all 10% ethanol.  We'll be coming off the winter blend soon and fuel mileage seems to pick up 10% so I'm not sure about the differences.

That's the way it is here in KC.  The ethanol percentage is allowed to go unlisted here in KS, so it varies from 10-15%.  Whether or not it's the winter blend makes a difference, too, but I notice it more in the car's mileage than in the bikes. 

From what Hondaman's book says, because of ethanol the octane rating actually increases, so the mid-grade stuff is closer to the grade that Honda intended back in the day.

Where I get really leary is when I look at all the fuel additives and carb cleaners out there (Stabil, Seafoam, Techron) wonder how many of them made adjustments for ethanol in their formulas.

[dave500]

all those additives you statesiders mention are unheard of here,,we dont treat fuel or engine oil for lay up or stuff like that,,i can leave my garden power equipment for a year plus and they mostly start straight up with the old fuel in them,or are you guys just fussy?i think it has to do with the lack of or lesser ethanol we have?

[trueblue]

I usually run our premium in my 650, only because when I have the missus on the back it will start to ping when the engine loads up if I run standard.  Also the premium is supposed to be ethanol free.  Ethanol is for drinking, not your fuel tank.  I have an old car out at my parents place that has fuel in the tank that is over 4 years old and it still starts and runs fine, no additives in the fuel.  It was parked up with half a tank of fuel and only gets run once every couple of months just to mow under it, everytime we just sit a battery in it and crank it up .

[bjbuchanan]

The additives are more prevalent here now because of the ethanol in the fuel. It turns gummy and deteriorates much faster now. There is also the brainwashing that this "treatment" will allow you to be lazy and skip routine maintenance

[bwaller]

I've heard (and I may be wrong) that high octane fuel packs a lower punch in engines that don't require it, due to a lower volatility. Slower flame propagation was the basis for such claims.

As mentioned already, 94 octane fuel in Canada is ethanol free and that could provide sufficient justification for the added cost. 

Jimmy I expect you're talking PetroCan 94? By my understanding it actually does contain Ethanol. What I can gather is (in the east) the only "premium" gas without E is Shell's V-power 91. I have been mixing C12 with PetroCan 94 for my race engine, but I may switch to Shell.

There are so many "half-truth's" out there it's damn hard to know exactly. Friggin big business/gov't B.S.

[FunJimmy]

Jimmy I expect you're talking PetroCan 94? By my understanding it actually does contain Ethanol. What I can gather is (in the east) the only "premium" gas without E is Shell's V-power 91. I have been mixing C12 with PetroCan 94 for my race engine, but I may switch to Shell.

There are so many "half-truth's" out there it's damn hard to know exactly. Friggin big business/gov't B.S.

The later statement hit the mark Brent.
Too much smoke and mirrors BS from government & oil companies.
I think Chevron 94 is ethanol free in the west as well.
I don't make a habit of avoiding ethanol blends anyway cause the Interceptor doesn't ping at 8000rpm. :-)

[Stev-o]

all those additives you statesiders mention are unheard of here,,we dont treat fuel or engine oil for lay up or stuff like that,,i can leave my garden power equipment for a year plus and they mostly start straight up with the old fuel in them,or are you guys just fussy?

No, most of us arent fussy! The ethenol affects the power equip, Ive had issues with a generator and multiple leak blowers that my guys use at work. 

[CrankyOldGuy]

For what it's worth ...  http://pure-gas.org/

Harry O.

[bbi]

cool forum here guys, yes I'm new but been around engines my entire life and thought I would weigh in on this. sorry its long.
there is lots of myths regarding fuel I work in the auto industry for a major Japanese MFG and raced cars for a number of years so I spent a lot of time on a dyno as we were fuel restricted... technically there was no legal fuel for our class, we couldn't run race fuel but we were not allowed oxygenated fuel which was all pump gas available in California.
If an engine was designed for regular fuel you will not gain power with premium assuming your running as designed.  I have tested this on a dyno over and over
if it feels more powerful your probably suffering from "clean car runs better syndrome" very common even I have had it..
deposits will not increase with premium, byproducts of combustion are the same regardless of octane any unburnt fuel will leave via the tail pipe hence higher emissions on older less optimized engines
Here in Ca we only can get E10 with a push toward E15.  10%/15% ethanol BTW the EPA is currently pushing through this requirement for all states, this is very political too.
Ethanol is bad for us older bike owners for a number of reasons, its corrosive, it attacks rubber, it has poor knock resistance, it has less heat energy per unit, it phase separates if left for more than a month(breaks down into its separate constituents and no run) it plugs pilot jets with a vengeance, the good is that it reduces emissions by a small percentage but on a modern car you will see a decrease in fuel economy but I don't think it cancels out the gain.
the AMA is fighting to prevent higher ethanol content only fuels due to the MC industry
the reason your car will get lower MPG with ethanol blends is that it adjusts the mixture as needed on the fly, your bike with fixed jets will just keep putting the same amount of fuel in no matter whats happening in the combustion chamber within reason.
as a side note you can get really high octane fuel at the gas station out of the diesel pump but I would not recommend that.
here's my take
I run premium all the time no matter what my engine was designed for and here's why,  it does give a level of knock protection and our older engines can go out of tune and put us into the danger zone quickly, vacuum leaks, points wearing, older crappy parts, the list goes on.... I also ride mostly 2 strokes the extra 75 cents a tankfull isn't going to kill me.
I'm sure there will be some disagreement with what I have said, if you look around the internet theres lots of information regarding fuel from SAE and other scientific sources.
Cheers

[Jim Harris]

Wow I've learned a lot, thanks for the information!

[bbi]

hope I didnt come off like a smart ass, I just thought I would share some things I have learned over the years.  Racing and industry forced me to trust testing and science over myth.  Funny thing is sometimes the myths are true but few know why. 

Cheers

[bwaller]

Thanks bbi.

[FunJimmy]

Thanks bbi.

+1, good info.
Thanks

[Retro Rocket]

hope I didnt come off like a smart ass, I just thought I would share some things I have learned over the years.  Racing and industry forced me to trust testing and science over myth.  Funny thing is sometimes the myths are true but few know why. 

Cheers

I have run higher octane fuels in most of my vehicles {except the diesels}, mainly to eliminate knocking and pre ignition on older engines, a side effect i found on one of my old cars was better fuel economy on the higher octane fuel, i didn't imagine that 
One more thing, on the same car i did experience a noticeable boost in performance low in the rev range, where my car used to knock, especially under load, it ran a lot better down low in the revs on higher octane fuel, i expect the difference was that when the engine was knocking under load it was struggling, therefore  loosing power, the higher octane fuel eliminated the knock and gave a boost in power.... Does that make sense..?   

[Mooshie]

hope I didnt come off like a smart ass, I just thought I would share some things I have learned over the years.  Racing and industry forced me to trust testing and science over myth.  Funny thing is sometimes the myths are true but few know why. 

Cheers

I have run higher octane fuels in most of my vehicles {except the diesels}, mainly to eliminate knocking and pre ignition on older engines, a side effect i found on one of my old cars was better fuel economy on the higher octane fuel, i didn't imagine that 

I found the same thing when I run 91 I get 50+ mpg's consistently, however when I dropped it to the lower octanes (89) I lost about 5 mpg's and a tad more with the 87.  It was not the most controlled study but I did go to the same gas pump for each fill up.  So I run 91 as I would rather have 15+ more miles on a tank

[bbi]

that makes some sense,heres some more pieces to that puzzle.
if your engine is knocking at any RPM your loosing power think of it like this... hit the piston with a hammer or push the piston down with smooth clean force which one is going to deliver more power (without breaking parts), also when you get knocking or technically detonation the fuel/air charge detonates in a violent instantaneous mannner and that will disrupt the boundry layer of air around the head, cyl, & piston allowing them to absorb majority of the heat, now that heat is no longer available to to expand the gasses and power goes down not to mention the other bad things the heat does to alluminum parts over time.  A lot of study has been done on boundry layer inside the engine.... ever wonder why aluminum doesnt melt when our combustion temp (3600 avg) is higher than its melting point (1250ish).. its the boundry layer that saves our butt and on two strokes we use it to our advantage when setting up squish bands to reduce end gas detonation.
A big misconception is that the air/fuel mixture explodes and that pushes the piston down, in fact it burns very rapidly and the heat expands the air and that pushes the piston down, most of the combustion process happens in the first 1/3rd of piston travel. check out this video shot in a combustion chamber,
Combustion Chamber
now if the engine knocks on regular and it was designed to run on it theres probably something causing that, spark timing, lean, compression raised by carbon deposits, slight oil consumption lowering the octane of the actual mixture hence why I run premium even when not needed.  Four stroke are usually more forgiving to detonation due to better internal cooling and more time between firing cycles, two strokes suffer because they snow ball once you start putting heat into the piston it heats the proceding charge in the crankcase and it escalates till parts come apart very rapidly I might add. dont ask how I know.....LOL also they fire more often for a given time period.
thats knock or detonation for the most part, pre ignition is another animal all together and very rare and usually results in engine salad by the time you realize whats happening.
The more you learn the more questions it raises and its very facinating whats going on in there and my last few posts just cover the tip of the iceberg..
Cheers all