OK guys, here's the skinny, Alcohol burns colder and is more resistant to spark knock ( Pinging or Detonation ) than gasoline. It also requires alot of heat to vaporize, not a good thing in cold weather.
All gasoline burns about at the same temprature and about the same flame speed.
Octane is a measurement of resistance to spark knock. Octane alone doesn't make a fuel burn "hot" or "cold" or "fast" or "slow".
If an engine will combust 87 octane fuel without spark knock, switching to a higher octane fuel ( with no other changes ) will not yield any horsepower or efficiency improvements.

 

Olso if you want to know more then most peoples brain can process email this man sorcer@means.net He is a fuel specialist with the navy His name is richard mcrath or mac for short he will tell you all you need to know.

 

CaptNemo hit the nail on the head.I would like to add that running higher octane(91 vs.87) than needed will not hurt at all,just wastes money.Race gas is a different story.This fuel burns so fast that I have seen it cause a flat(lean)spot in throttle response in a streetbike.in conclusion,if your machine is stock compression and ignition timing,follow the manufacturer's recommendations.They know what they are talking about.

 

Thanks for all of the replies. The 425 Magnum does have a little spark knock when it is cold, but goes aways after the engine warms up. I think I will stay with the 87 octane as it appears there is no benefit to upgrading.

 

Mag-Man, This post seems to have gotten off your original question of cold weather starts. A lot has been posted about octane and most are correct, (except the one about octane being an additive) Somthing that hasent been discussed is the RVP, (Reed Vapor Pressure) this is the measurment of how much vapor is being released by the liquid gas. Remember, you are burning the vapor not the liquid. In cold weather climets, a seasonal change in the RPV is needed to aid in cold weather starting. Here in the interior of Alaska we raise the RVP in the fall so the liquid will give off enough vapor to allow the spark to ignite it. In the summer it is lowered to prevent vapor lock and other heat assocated problems. The higher RVP helps give you a richer mixture when starting your rig. I don't know if this is a pratice in your neck of the woods or not. if not, this can be a piece of the puzzle on why it's more difficult starting in cold weather.

 

Seacow

Thanks for the info. The Polaris website has a tech article about the RVP on their website under the tech tips. The article says that the typical northern stations change their RVP in the gas about 3 times a year. It has been in the single digits for a about a week here and the Magnum starts right up, but I have been running it about every day. I think I will just stick with 87 octane and keep it fresh.

 

Good discussion on fuel and winter starting. Knock, or ping is caused by DETONATION. It is caused by improper timing, or to low of octane for the compression of your engine. On a high compression engine the fuel vapor is ignited to soon on the compression cycle, and you get the knock or ping. By using higher octane fuel, the fuel air mixure will ignite SLOWER, allowing the piston to reach TDC, allowing for full transfer of energy. If you continually run your engine with a severe knock, or ping, you may eventually blow a hole right through the piston.

 

Detonation: What is it?? Ok boy's we have a can of worms opened here. Read on if you want the tech. talk on what's going on in your engine when it's "pinging"
Detonation is sudden, explosive combustion of part of the fuel/air mixture, after the combustion process is mostly complete.
Heres how it works.
Compresion and combustion cause heating of the yet-unburned parts of the mixture. This heating breakes apart some of the weaker molecules to form highly reactive species called "radicals". When the population of these radicals rises high enough (because of the cumulative heating of compression and combustios), the last tortured bits of charge to burn go off by themselves, before the normal flame front can reach them. because they are now so chemically changed and reactive, they burn at supersonic speeds, forming shock waves. These violent pressure fronts do two things. (a) accelerate heat transfer by scouring away the thin insulating boundary layer of stagnant gas that normally clings to all surfaces and (b)can then blast heat-softened metal out of piston and cylender head surfaces, leading to failure. So all said and done, just keep the octane gas in your rig high enough to not encounter "knock" or "ping" or "deto" for the compression you have, and all is well. I'll try not to be so long winded on this in the future.
seacow.

 

Great post.

Also, if your engine has a tendancy to overheat use the premium fuel, otherwise if it does not overheat or ping use the 87 octane and get more bang for your buck.

Our local "Victory Dealer" maintains that premium fuel in the Victory motorcycle will cause bluing of the pipes because of the delayed burn farther down into the exhaust pipe.

 

Just bringing to the top for the benefit of Mega Crash