What kind of gasoline do you use?

Here in new zealand we have 91 octane and 95 octane, I use 95 in my xj, i think the the lead content in the 91 is to low and it needs to have additive to increase the lead content, so i dont touch it as it could damage valves etc. Would be interested to know if this would be the case from any experts out there

 

You guys still put lead in your gas???
We haven't had lead in gas in a very very long time around this part of the world!

 

its un leaded but some older vehicles dont seem to run on it that well and you can put an additive in it which i assume increases the lead content. I think the unleaded fuel can damage some older engines resulting in excessive wear to parts. i was wondering if others had the same results with there fuels or excessive wear

 

No gas here has lead and the additives are lead free as well, they contain mainly kerosene. The additives are to prevent damage to the head where the valves seat. Older engines heads valve seats are made of soft metal where the new ones have hardened valve inserts thus lead (or additive) is not needed.

I have used the 3 grades of fuel in my XJ, 95 ran OK but left soot in the head and pipes, 98 sooted up so bad that after 30 or so Km the bike started running bad and after a couple of sort trips would not run at all due to the plugs fouling. 91 the bike runs fine. Regular is what is called for (by Yamaha) in these bikes (apart from the turbo or you have upped the compression or you have the Ethanol problem).

As my bike is EFI I know jetting is not affecting my findings.

Octane rating explained

 

Here in Eastern Canukville, we get 87, 89 and 91. Tried all the varieties and found that 89 & 91 simply waste cash. I get no better mileage and maybe worse and the bike is harder to start. The higher the octane, the higher the resistance to burning, so unless your Yammie experiences spark knock, regular is the way to go.

 

I must be confused as that is certainly not what I have been led to believe. In fact my understanding is that the higher the octane the faster it burns producing more heat.

 

I use the highest octane at any station I go to. :wink:

Chuck

 

" "It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion).

A simple explanation is that carbon-carbon bonds contain more energy than carbon-hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating. A premium motor fuel will often be formulated to have both higher octane as well as more energy. A counter example to this rule is that ethanol blend fuels have a higher octane rating, but carry a lower energy content by volume (per litre or per gallon). This is because ethanol is a partially oxidized hydrocarbon which can be seen by noting the presence of oxygen in the chemical formula: C2H5OH. Note the substitution of the OH hydroxyl group for a H hydrogen which transforms the gas ethane (C2H6) into ethanol. To a certain extent a fuel with a higher carbon ratio will be more dense than a fuel with a lower carbon ratio. Thus it is possible to formulate high octane fuels that carry less energy per liter than lower octane fuels. This is certainly true of ethanol blend fuels (gasohol), however fuels with no ethanol and indeed no oxygen are also possible.

In the case of alcohol fuels such as methanol and ethanol, are partially oxidized fuels and need to be run at much richer mixtures than gasoline. As a consequence, the total volume of fuel burned per cycle counterbalances the lower energy per unit volume, and the net energy released per cycle is higher. If gasoline is run at its preferred maximum power air/fuel mixture of 12.5:1, it will release approximately 20 MJ (about 19,000 BTU) of energy, where ethanol run at its preferred maximum power mixture of 6.5:1 will liberate approximately 25.7 MJ (24,400 BTU), and methanol at a 4.5:1 AFR liberates about 29.1 MJ (27,650 BTU)." "

 

Hey olebiker, this was an tidbit gleaned from R&T's Dennis Simanaitis in one of his Tech Tidbits articles years ago. The reason that straight hi-octane gasoline reduces or eliminate spark knock (aka pre-ignition) is because it will not light off early. It resists early ignition due to pressure and temperature better than low-octane fuel. Dennis and I (and Rick) are not just pretty faces - Dennis is an engineer and I am...well, a grocer...that wants to be an engineer. Thanks for your Super-Tech answer, Rick. XJB counts on you for a reason.

 

What Rick said was far over my head. I know for a fact that higher octane burns faster it must be that compressing it causes delayed ignition. I'm still not sure I believe it though. I am not an engineer but take a gallon of low octane pour it out and light, now try that with higher octane. Better stand back a bit as I have seen a guy get singed trying this out.

 

What Rick said was a quote from the Wiki artical I posted a link to above.

Read the whole artical and also follow the links from it for more information.

These bikes require regular, the problems arise when ethonol is added the ethanol needs to be much richer to run.

Also read:

http://www.prime-mover.org/Engines/GArt ... ctane.html

and

http://www.offroaders.com/tech/octane.htm

 

Yeah, the chemistry is over my head as well. Keep in mind that the two examples feature entirely different conditions (liquid fuel vs. atomized fuel, 9:1 compression vs. atmospheric pressure) and in the open flame test alone there can be a lot of variables.

There may be more energy in hi-octane gas but also keep in mind that the ignition points for each fuel are low enough that a match, a spark or a blowtorch are all going to get the job done to make it light off. The difference is ignition under pressure and hi-octane resists that better.

Diesel resists it even more. That's another discussion entirely.