I topped off with 89 today. What do you guys run , and have you noticed any knocking?

 

87. Unless you have modded your 650, you are wasting money running anything higher.

 

I do know the additive package and detergents are better in the higher grades of gasoline, and supposedly less contaminants/byproducts....then again i've heard the engines are designed to run on 87 and run best on it....

 

87 should be fine(with mo mods) to avoid detonation. Lightman is right about the additive package. Fuel quality varys by region. I was on a team once and we tested 30 different station's pump gas and only one met even minimum standards for cold weather stability, silicone content, and fungus inhibitor content. (Amoco white)

 

Correct me if I am wrong...but doesn't the manual call for 93? My manual is locked up, and I don't want to go get it...but I am almost certain 93 is what is recommended. I ran "regular" for a while, but stepped up to 93, and man, there IS a difference.

Chucky

 

My 6-5-o also seems to run A LOT better with the higher octane.

I'm not going to go any higher than what the regular pumps offer though....too expensive, it sure does like it's gas.

 

Look under the seat, take seat off turn over.
Let see min. octane is 91, or it will run lean, too lean !

Compression ratio is ------- ? 10 or 10.5 to 1.

 

My bad. Compression ratio is 9.9 to 1. I was told by somebody not to bother running higher octane. I haven't had any knocking or pinging running the 87 though.

 

Octane has nothing to do with horsepower, or mixture. You will not get a HP increase by running higher octane*, nor will you run lean running lower octane. The octane rating on gasoline is an indication of the temperature the fuel will ignite at. Lower octane fuel will ignite at slightly lower temperatures. Higher octane fuel is used in high compression engines because lower ocatane fuel can pre-detonate from the heat generated by compression coupled with remaining cylinder heat after the engine has been running. There is also evidence of glazing and varnishing of valves and cylinders running higher than needed octane, but everything I've found on it has been anectdotal.

Most engines in good condition, regardless of compression, will run without pre-detonation with basic unleaded. Pre-detonation generally comes into play at compression levels of 12:1 and higher, or slightly lower in engines with severe cooling problems. This can be affected slightly by elevation. Engines running at high elevations can usuallly run a lower octane than they could at sea level without detonating. My current and my last motorcycle ran at 11.5:1. I never ran more than basic unleaded, and I never had pre-detonation or dieseling.

Added HP is a common misconception. Go to your local airfield and talk to the people running the fuel trucks. Every weekend they'll have people buying Avgas to run while they drag race. The average motor is running between 8-10:1 compression and they are dropping about $4 a gallon (on top of the cost of the fuel in their tank). If you ask they will tell you how much faster their car goes w/high octane. But I'm sure there are some that know their car is faster now that they painted it lime green and added 400lbs of spoiler and body trim.

*Either Hotrod mag. or Car Craft did some independant testing on octane levels and performance. They used regular unleaded at 85-87 octane, premium at 91-93, and mixed some up to 140 octane if I remember correctly. Running the same motors back to back through the octane levels they found no HP or torque increase in any engine, and occasionally lost a point or two. Of course no two dyno runs will be exactly the same. This held true in all cases except NASCAR HP level engines. At that point the found 4-5 additional HP running 140 octane.

So in summary, unless you really like spending the money, run the lowest octane you can until your engine exhibits pre-detonation or dieseling, then step-up a level.

regards.

 

AJ650 is right. Higher octane fuel also burns slower. We ran a 9 to 1 motor in a race car. The motor will make more hp with lower octane gas, but run's higher exhaust temps. The higher octane will handle more timming advance and help keep cylinder temps down.
Tim