Do we need to use higher octane fuel?

[lego1970]

My 98 F-150 knocks on anything less then 90 octane (been that way since new) and my Generator with a Subaru motor doesn't start or seem to run well on lower octane ratings. Everything else I own runs just fine on 87 octane. Never really have checked the fuel mileage difference though. That might be kinda interesting.

[SpudRider]

Originally Posted by SpudRider

I use 85 octane fuel in my Zongshen 200GY-2, and it runs like a champ. My owner's manual from Zongshen recommends the use of 90 octane fuel, or higher. However, foreign octane ratings are calculated differently than U.S. octane ratings; check out the following link.

http://hondaswap.com/reference-mater...ratings-59435/

According to the information posted above, 90 octane in China would be equivalent to 85.5 octane in the United States. Another factor to consider is elevation above sea level. I live and ride at elevations 4,400 feet above sea level and higher. At higher elevations the air is thinner, and lower octane gasoline can be safely used without causing engine pre-ignition. In Idaho and Utah regular grade gasoline is 85 octane.

Spud

The engine in my Zongshen 200GY-2 has a compression ratio of 9.5:1. For a month or two this summer I experimented with several different grades of premium, higher-octane gasoline. I never noticed any significant difference in either performance or gas mileage from regular, 85 octane gasoline.

I guess that the best advice is to follow the recommendations of your owner's manual, experiment, and choose your octane accordingly.

Spud

[TheRealWorld]

Thanks for the reply. By the way lego1970, I have a 98 Ford 150 that I bought new that has always run fine on 87 octane. Maybe you should check your timing.

[lego1970]

TheRealWorld, Yep, my neighbor has a 2000 F-150 with the same motor and his runs fine on 87octane. Thruout the years I've tried different plugs, wires, coil outputs, cleaned and checked the injectors, etc with no luck. I've taken it to Ford a couple times over the years for other routine maintanance and had them look into the knocking thing and I'm assuming they have checked the timing but with no luck. I'm also assuming they checked the oxygen sensors. Aside from being picky with fuel the truck has performed flawlessly over the last 10 years so I'm not too worried about it, but yea, it's always baffled me how other F-150's can run on anything. Likewise one of my other cars in the past called for 89 or greater octane and I always 87octane with no problems. My 07 VW Rabbit seems to run well on anything but after reading this thread I'd like to check the fuel mileage difference between the grades of fuel. My sportbikes in the past running 11:1 compression seemed to take 87 octane just fine.

[suprf1y]

Originally Posted by elroyjetsn

Ethyl Alcohol is about 130 oct and far superior to gas- Leaves no deposits, no emissions and completely water soluble. You can cut it with 20% water or more and it'll run ok- jetted properly of course.

I think you're the first person I've heard tell the truth about ethanol.
For whatever reason, most people think its terrible stuff, but its quite the opposite.
For the record, my KLX250s has 11-1 compression, and runs fine on 87 octane.

[culcune]

Back to the original question and what I use--super unleaded just because I only need 2 gallons to fill up, and it only costs an extra $.40 to do so, and helps me "sleep better at night."

[SpeedSouth]

I was reading about this very subject a few days ago (last week sometime) but, as luck would have it, I can't find that thread now.


Anywho...the gist of what I gathered from that discussion was....motorcycle engines can often get by with higher compression and lower octane levels due (at least in part) to the smaller sizes of the combustion chambers.

Car and truck engines generally have much larger cylinders, and therefore require a higher octane rating when compared to the same comp. ratio in a motorcycle engine.


But, again...this is just my limited understanding of what I was reading from others. It seems to make sense to me, but I'm rather ignorant on the subject.



I use the cheapest gas I can find...in everything I own.

[elroyjetsn]

Originally Posted by suprf1y

For the record, my KLX250s has 11-1 compression, and runs fine on 87 octane.

Hmm, Must be running a very conservative spark curve to prevent knock...

Does the owner's manual for your KLX recommend 87 oct?

Knock on a small engines sounds different from a car engine and it can be mistaken for normal engine noise.

The sound reminds me of breaking ice- dull banging.

[suprf1y]

87 is recomended, and it does knock if I lug it, which I don't.
Combustion chamber/piston design, number of valves, spark, and valve timing, as well as load, and jetting are all signifigant factors affecting octane requirements.

[SpudRider]

Originally Posted by SpeedSouth

...I use the cheapest gas I can find...in everything I own.

Amen!

Spud

[katoranger]

I did have to run premium in my GPZ550. It just wouldn't run right on anything less than 91.

The lifan has giving me no issues with 87. I like low tech.

Allen