What octane?

[abbo]

I am relatively new to this forum and have owned a 2001 Nomad just 3 months. I currently alternate between 87 to 92 octane every couple of fills(no pinging). I am going to Colorado next month and am wondering what octane to use!! I just ran 2 tankfuls thru with seafoam and mileage went up from 38-40mpg to 43-45 mpg. This stuff is so great i wonder if it would be good for human consumption(just kidding) it is a great product that I picked up on this site. Any help would be appreciated. Thanks Dennis

[Top Cat]

With the price of gas going up daily, the general consensus is use the lowest octane that does not make your bike ping.
I have run 87 and only had slight pinging. I now use 89 and so far so good. My bike is stock.

[cactusjack]

I think BD said Seafoam was great on lasagna? ;)

[VulcanE]

I have come to the conclusion that the time of the year will dictate what octane I can run. I was running regular (87) with no problems, bike ran strong. As the temps started coming up, I have moved through (89), and now in the mid to upper 90's, back to the (93). The mid-grade wasn't no different than the regular, so in late fall I will switch back to regular. All of this is to keep the bike from pinging, and run the lowest cost fuel possible

[aj]

Did someone say Seafoam helped restore hair??

Abbo,welcome to the forum from Nebraska.

[dkdixie]

What octane?

Whatever runs without pinging. Absolutely no reason to run 92-93 if bike runs OK on 87-89.

For some reason, my 08 seems to like 89. I suspect every bike is different.

Octane affects the flash point of gasoline, period.

The flash point is the point at which the vapors from the fuel will ignite by means of heat, instead of spark.
It's also known as 'dieseling'.

Just to help clarify some terms also:
Pre-ignition, detonation, pinging, are not interchangable terms.
Pre-ignition is when the vapors ignite from heat, not spark.
Detonation is what happens AFTER pre-igntion occurs.
Detonation is the result of two flame fronts (one by pre-ignition, the second by spark) colliding in a massive release of heat energy.
Pinging/Spark Knock is the noise you hear as a result of the two flame fronts colliding.

The amount of pressure present in the cylinder will actually surpress spark combustion. One of the many reasons that high boost engines require very small spark gaps and very high ignition voltage.
The more compression you have, the higher the electrical resistance is present and the harder the plug is to fire.
However, the more compression you have, the greater the change of pre-ignition there is... that's why high compression engines detonate so easily.
Ever see a Top Fuel motor? They run DUAL 44amp magnetos putting out about 70,000 volts, each... and spark plugs in the 10 and 11 heat range with a gap of only .015-0.017".

All you are doing by increasing octane, is increasing the point at which the gasoline vapors will ignite by heat. When you change the compression ratio, you change the heat level. High compression generally generates higher combustion temperatures.

Now, if you take a 12.0:1 compression engine at 90 degree ambient air temp, and run it on 87 gasoline... will it ping? Possibly.
Compression is NOT the only thing that makes an engine ping.
Take that same 12.0:1 compression engine and take it where it can run in 40 degree ambient air... Likely, it will not ping. You could likely even increase the compression ratio to 12.5:1 and still not have it ping.

Just another thing to throw in to the mix.
In general, the slower a fuel burns, the more power it can produce.
That is generally the case in most all fuels... even gun powder.

It's all a balancing act, really. You can't just say that high compression engines need higher octane gas. You HAVE to factor in the enviroment(termperature and altitude), the cylinder head design, etc.. There are MANY factors that determine whether or not an engine will detonate.

However, if you live somewhere that has extreme heat (such as parts of California, Arizona, New Mexico, etc...) a higher octane gas may be needed as your outside air temp rises.

So, why do some people notice a difference in power when switching to high octane gas? Well, likely, they live in an environment that makes it necessary. If you have aftermarket exhaust on your ride, you may not hear the pinging.. Switching to a higher octane gas IF your engine is pinging can and most likely will result in better gas mileage and more power. Why? Well, let's look at the cycle of an engine.
On the intake stroke, the cylinder takes in an intake charge that consists of gasoline and air. As the piston moves up on the compression stroke, that mixture starts to heat up. If it gets too hot and flashes before the spark ignites the fuel at the appropriate time, the flash point flame starts burning bottom to top. Not the way you want the flame to burn. You want a downward expansion. Now, as the bottom flame is burning upwards, the spark plug ignites the mixture and starts burning top to bottom.
The two flame fronts collide and all that energy that would normally be used to push the piston down has exerted much of itself upwards and outwards as the flame rises and collides. This force is also trying to push the piston back down as it's trying to come up in the hole.
Now, switch to a higher octane gas and the gas is resistant to the heat generated by compression and outside air so that the plug ignites the mixture at the appropriate time. Now, the expansion of the exhaust gases are expanding correctly in time with the piston. As the piston travels over TDC, the expanding gas can push the piston back down in the hole with the majority of it's energy. So, does pre-ignition cause power loss? Absolutely. Will higher octane fuel help? Absolutely. Will you get more power by running higher octane fuel? Yes, in a case where pre-ignition is robbing the engine of power. Will it always give more power? Nope. If it's not detonating, the higher octane is not doing anything.

And no, higher octane doesn't burn any cleaner or dirtier than low octane gas.

Originally Posted by Aj

Did someone say Seafoam helped restore hair??

Naw, I think it's used for ED

[ringadingh]

I ran my bike from north of Toronto to the Eastern Rally in West Virginia, all I used was regular gas there and back. It didn't ping or knock at all regardless of wether I was in the mountains or not.

[Cajunrider]

Very good explanation trjam. I wasn't aware of the different burn directions with pre ignition and spark ignition. Makes sense. That generates trememdous pressure in the cylinder thus punishing the piston and connecting rod, etc.

I am fairly confident in the octane rating for the Nomad to ensure for proper burn detonation.

[dkdixie]

Originally Posted by trjam

I am fairly confident in the octane rating for the Nomad to ensure for proper burn detonation.

I hear ya......and understand why you feel this way.

But, I'm also confident my 08 runs better on 89 than 93 with TFI installed.

[flightdoc]

I'm bummed.....I thought if I ran high octane gas and used seafoam I'd increase my mpg by at least 10 and increase horsepower by 50...at least!!
Oh well. I'll just leave it stock I guess.

Thanks for the in-depth explanation trjam.

[rlfaubion]

Yeah, but.... well that's fine. Still, I heard Nico needed to fuel up before leaving Mesquite Nevada, but filled his tank with seafoam instead, and made it non-stop all the way to San Diego?