id like to set something straight

wolf21432

New Member
Dec 23, 2010
12
0
0
CT
I keep reading on here about people using premium gas and racing gas. I would like to say this to them. Octane in the fuel slows the burn rate of the gas witch reduces the power it creates. The reason race cars use 100+ octane fuel is because it reduces engine knocking and premature burning of the fuel. When you use it in a low compression engine it will reduce the power it creates because it will not burn as fast. So please remember just because its race fuel or premium it will not make u go faster. The only reason to use any higher then 87 is if your engine knocks.
 

2door

Moderator
Staff member
Sep 15, 2008
16,332
137
63
Littleton, Colorado
Thanks for reinforcing what many of us have tried to explain to people. If we were all running 11:1 or higher compression then there might be some advantage to using high octane fuels. Fortunately, that's not the case. 87 is a far better choice and will serve you well.
Often the psychological effects of something will have more impact than the actual thing. I believe that's often the case when folks preach about the power increase they get with premium fuels, high velocity air cleaners, loud exhaust (not including expansion chambers) and some of the other bolt on performance gadgets currently available for these simple little engines.
LOL, I swear my car runs quieter and smoother right after I wash and wax it...but does it really?
Tom
 

peeduh

New Member
May 27, 2009
28
1
0
Texas
it also burns better and saves gas, at least it does for fuel injection9not sure on the whole power gain/boost-when touring across the country with my band, every time we used non-premium we lost gas mileage. After that evidence I think the whole band tried to use premium in their own vehicles haha.
 

wolf21432

New Member
Dec 23, 2010
12
0
0
CT
you might gain slightly higher mpg but think about this. your revving higher for the same power witch in turn burns more fuel for the same speed. so in your case it was most likely a placebo affect. Also it depends on were your driving. the only way u will be able to test if it improves mpg is to drive on a track the exact same way with both fuels. like you said cross country so with the regular u could have been going up hill decreasing mpgs while when u were on the premium u the rode might have been flat or downhill thus improving mpgs. There is way to many variables that affect mpgs. but its you money so use it the way you want. personally I'm getting a MB to save money so i will be using regular fuel.

And 2door I swear I can run faster after I shower =D lol. If people were to just understand why octane is in gas they would rethink putting it in the engines. I took only a HS shop class and learned why it is in there so it dosnt take much to learn it

PLEASE PEOPLE LOOK UP WHAT OCTANE DOES IT WILL CHANGE YOUR LIFE =D jking but seriously look it up.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,620
429
83
Los Angeles, CA.
I use 91 in my bikes... I know that the extra octane does nothing in these low compression engines, but I've also used the low octane stuff & I swear that my bikes run a little better on the good stuff!! (Maybe it's because of the other chemicals that are in the good stuff?) :rolleyes:
 

matthurd

New Member
Dec 13, 2010
817
2
0
manchester NH
I use 91 in my bikes... I know that the extra octane does nothing in these low compression engines, but I've also used the low octane stuff & I swear that my bikes run a little better on the good stuff!! (Maybe it's because of the other chemicals that are in the good stuff?) :rolleyes:
another thing is watered down fuel, companies in most states are allowed to sell gasoline with up to 15% water content before it becomes a problem, i'm willing to bet that their higher end fuels will have more actual fuel and less water content, which i think would help a bit more.
 

peeduh

New Member
May 27, 2009
28
1
0
Texas
our tour van also idled rougher with the cheaper stuff as well. But I'm sure if a van full of street punks took a bath then we'd have been way lighter!! hahaha
 

scotto-

Custom 4-Stroke Bike Builder
Jun 3, 2010
6,508
11
38
Ridin' inSane Diego, CA.
A little water will keep your combustion chamber and piston top cleaner as well, but I don't recommend it. What octane do you think I run in my 15:1 compression 2-stroke? (hint: it's not 89)
 

cigron

New Member
Nov 18, 2009
59
0
0
wormleysburg pa
Octane rating has nothing to do with how fast
Or slow your gas burns. Octane rating is the means
Of measuring the fuels ability to with stand heat
And pressure before it explodes. The power that the
Fuel makes is measured in btu. Before they add the
Anti knock compounds it`s all the same.
If it does not knock. Your good to go.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
6,620
429
83
Los Angeles, CA.
another thing is watered down fuel, companies in most states are allowed to sell gasoline with up to 15% water content before it becomes a problem, i'm willing to bet that their higher end fuels will have more actual fuel and less water content, which i think would help a bit more.

That's a very good point!, & for the extra 60 cents that it costs me to fill my 3 gallon container with 91, I don't worry about it. ;)
 

Goat Herder

Gutter Rider
Apr 28, 2008
6,248
12
38
N.M.
To me it really depends in what part of the country your in. 10 years ago I lived in Austin Texas . There gas is different than here in Albuquerque N.M. Ask me how I know. As for fuel I find a gas station sometimes that has just refueled and its better gas. As for a gut instinct. You don't know what shape the in ground tanks are in.

Yes I have a few preferred gas stations . Why I can tell the difference with my little motors as well as my big truck and they change over time too. This is how I got a faster M.B. bike than my buddies in my opinion when we on rare occasion raced. My two stroke mix I don't let sit around for more than two weeks. The performance of the fuel goes down hill unless you can keep it as cool and safe as the in ground tanks. All of my little motors are hot rodded for as much compression as I can get out of them performance wise. On a hot July day here at 5500 foot above sea level they will run crappy on bad fuel its a given.

I ran my Morini on race track high octane race fuel and the gas millage was outstanding!
The pep and performance jumped up substantially too. Night and day difference.............

One of the main things I am getting at is depending on the region you live in well. The gas every where is not the same all the time or the altitude. Nither in my experience go hand in hand ether.

What I am getting at find what works best for you.
 
Last edited:

wolf21432

New Member
Dec 23, 2010
12
0
0
CT
well im just gonna stick to my regular gas. its cheaper and does what it needs to do. also i find it a waste putting high end fuel in a low end motor if it was built to be reliable and give out better hp i would be more then happy to put higher grade fuel in it. but they way i see it is cheap engine = cheap gas.
 

ferball

New Member
Apr 8, 2010
599
1
0
NH
well im just gonna stick to my regular gas. its cheaper and does what it needs to do. also i find it a waste putting high end fuel in a low end motor if it was built to be reliable and give out better hp i would be more then happy to put higher grade fuel in it. but they way i see it is cheap engine = cheap gas.
True that. My old VW bus actually runs smoother and gets better MPG on the dirtiest nastiest gas I can find. High octane does not run as smooth for some reason, I say this from actual experience and calculating MPG I have know idea why but I get at least 2-3 MPG more with nasty gas. I also get about 125 miles to the gallon of oil, it is probably due for rebuild, or at least a tune up.
 

wolf21432

New Member
Dec 23, 2010
12
0
0
CT
well Germans have always been backwards especially with their cars. so that doesn't surprise me. lol
 

Sideshowbob

New Member
Dec 26, 2010
64
0
0
Salem OR
My bike is a land yacht and I weigh 190, so when I am cuzing I am genreally from 3/4 to full throttle. I is correct to say that higher octane gas is less volitile and has better antiknock (predetonation) properties. Remember these little motors are very primative and in most instances low octane gas is fine and burns more eisily. But lubrication is key in 2 cycle motors and lube is required for valve guides in 4 cycle one. I don't think it really makes a hill of beans difference in speed. But higher octane is less likely to predetonate in higher compression engines. A fuel with a higher octane rating can be run at a higher compression ratio without causing detonation. Compression is directly related to power and to thermodynamic efficiency, so engines that require higher octane usually deliver more motive power and do more work for a given BTU or calorie of fuel. Power is limited by the maximum amount of fuel-air mixture that can be forced into the combustion chamber. When the throttle is partially open, only a small fraction of the total available power is produced because the manifold is operating at pressures far below atmospheric. In this case, the octane requirement is far lower than when the throttle is opened fully and the manifold pressure increases to atmospheric pressure, or higher. Since switching to a higher octane fuel does not add any more hydrocarbon content or oxygen, the engine cannot produce more power.
I do think in high compresion full throttle situations it will provide more lubrication and less predetonation (knock). I think I run high octane cuz I'm at full throttle often. But it sure ain't giving anyone more power. For more power try good bearings, port, polish, and BALANCE crank and piston will make the most difference. But a boost bottle could increase fuel efficiency just a bit. Just how much hydrocarob and O2 can you ram in there thats what counts for power. sorry for babbling on. usflg
 

Sideshowbob

New Member
Dec 26, 2010
64
0
0
Salem OR
Re: Hydorcarob mmmmm ggood

ooopppsss fat finger. I have been wondering if a trumpet bell ram air might force a few more O2 atoms in the intake but it won't work for me in Oregon I need a snorkle cuz of the constant rain. interesting thought for guys like in Tucson.
 

tim turbo

Member
Nov 18, 2009
186
1
18
fergus falls mn.
The reason I use 91 octane gas, is the simple fact that it,s the only gas I can get without ethanol in it. Non oxygenated fuel in Mn. is the only way to go!!!! Ethanol is not the answer to our energy problem's!
 

Hammond Egger

New Member
Oct 23, 2010
270
0
0
Tucson, AZ
I bought a generator with a 13hp 4 stroke motor on it today. The instruction manual says to use at least 91 octane gas. I seriously doubt that the motor is high compression.