Motorcycle Forum banner

1 - 10 of 10 Posts

·
Registered
Joined
·
67 Posts
Discussion Starter #1
Realizing that the manual for the S50 and Intruder VS800 call for 87 Octane gasoline to be used, I believe that many times the octane rating can be wrong and to use lower Octane could, at the very least, cause a loss of power. I have been using 89 Octane. Is there any advantage to using 93 Octane? Any chance of damage to the engine using 93 Octane? Is going from 89 to 93 Octane simply a waste of money? Since I am getting right at 50mph, the additional cost of the higher Octane is not important.
Steve in Md.
 

·
Still crazy after all these years
Joined
·
14,179 Posts
No.

We discussed this in the Sportsbikes section a few months back. Octane simply specifies how "volitle" the fuel is - a lower octane gas can ignite prematurely (before the piston has hit the top), causing engine damage. Using a higher octane fuel than the engine was designed for can result in incomplete burning, if the spark plug is too weak to ignite the fuel properly. If the owner's manual says to use 87, then use 87. Anything higher is just wasted money, and won't give you any noticable power boost.
 

·
Registered
Joined
·
864 Posts
a higher octane will actually cause a loss of power as well. There is a reason the engineers said to use a specific octane, use it and be happy
 

·
Registered
Joined
·
57 Posts
Is that really true....because in cars...I have and RX8...and with sports cars they always say a minimum. Like use 91 or higher. Even my Wife's Mazda 3 says use 87 or above. So it would seem like they are engineering these for a minimum...and anything above that would be better for power, quicker starts, etc,.

FWIW (For What its Worth)
 

·
Registered
Joined
·
864 Posts
They say to use minimum because not every gas station has the same ratings on their pumps. I can't really explain it but I know that using a higher octane than what you are rated for has been proven on dynographs and racetracks to lower your hp.
 

·
Still crazy after all these years
Joined
·
14,179 Posts
It depends alot on the engine. Over here we use the RON method, so "Regular" is 93 RON, "Super" is 95 RON and "Super Plus" is 98 RON.

Shell and Aral/BP have started selling 100 RON (Ultima / Optima) gasoline - for about 5% more than Super Plus.

Several magazines tested this new fuel in different engines, and found that in the best case, there was NO DIFFERENCE to using what the manufacturer recommended. In the worst case, the more expensive fuel acutally caused a 5% power loss and lower mileage.
 

·
Site Admin & Squeegee Boy
Joined
·
4,424 Posts
It comes down to engine compression, in other words by what factor the air/fuel mixture will be compressed during the combustion phase.

At the beginning of the piston stroke air and fuel are blown into the cylinder at atmospheric pressure then as the piston rises it compresses the mixture which is then ignited by the sparkplug. Higher compression of the mixture can cause the mixture to self detonate without the help of a spark ( this is the way a diesel engine works ).

In higher compression engines, say above 10.5 to 1 ( in other words a volume of 10.5 cubic inches of air/fuel mixture is compressed into a 1 cubic inch space ) regular 87 octane fuel can self detonate before the optimum moment in the combustion cycle.

In lower compression engines using too high an octane fuel will do the opposite that is to say it will underdetonate or rather detonate too late in the combustion cycle to properly burn all the fuel which will then be partly blown out of the exhaust.

What you want to achieve ( and this is why the engineers tell you to use a certain octane rating in your owners manual ) are the optimum combustion conditions, by having the spark set so that it ignites the air/fuel mixture at just the opportun moment when the mixture is compressed to a fraction away from self combustion. This is the point where you will get maximum power and performance from the combustion cycle.

Anything else will cause knoc, detonation, power loss, decreased fuel mileage and in extreme cases engine damage.
 

·
May 2007 Member of the month
Joined
·
7,992 Posts
In automobile engines when you get some miles on them you can see where the engines will run better with a higher octane gas,,, things like valve rattle will be minimized, better acceleration,etc. Alot of this is due to wear on the rings, valve stem seals, cylinder wall scarring, and carbon deposits.

Engines with alot of carbon deposits will detonate prematurely due to the "Hot Spots" that develop in the combustion chamber. These carbon deposits build and store heat and that excessive amount of heat will ignite the air/fuel mixture prematurely and thus cause early detonation. The easy way to solve this is to run the higher octane as to where it will take longer for it to detonate and thus somewhat restore the correct point of detonation.

Or manually remove the deposits by either strong fuel cleaners(if it is not too bad) or by manual physical removal(engine rebuilds).

When you have a newer engine run the correct octane to where you don't have post detonation.

Also remember to do frequent oil changes,,, sludge that builds up in an engine also causes hot spots to develop and thus increasing the engines operating temperature as to where the early detonation can occur as well.

That is why proper service is the key to keeping the engine alive for years to come.
 

·
Registered
Joined
·
5,197 Posts
Just start with the cheep stuff. If the engine does not pre-detonate, knock, or ping, keep using it. If it does, try the next step up. If it knocks andpigs on the mid-grade, try the super. if it only runs well on super, have the bike tunes up 'cause something ain't right'.
I use the mid-grade in my 800s, because sometimes a tank of the cheep stuff will ping a little. My first 800 went 132,000+ miles before dying of low oil pressure from a leaking filter gasket, and the new one has 24,000+ miles on it in just 7 months with no problems, so I don't think it hurts to have the 89 instead of the 87.
 

·
Registered
Joined
·
45 Posts
On advice of the stealer, I tried the higher octane also in my VS800/S50. Noticed occasional backfiring and poor acceleration on 93 oct. Switched back to regular 87 oct. and things seem to be better again.

Problem is psychological, here in America we've been indoctrinated that more expensive with higher numbers always means better. The octane rating system seems to work in reverse, and some of us will just never be comfortable with that. Since it's all about having fun, I think you go ahead and use whatever grade makes you happy and just accept the results.
 
1 - 10 of 10 Posts
Top