i recently bought a 400ex and was told by the owner that he ran 91 through it. the motor has a supposedly stock bore. just wanting to know if anything can be damaged by running with a somewhat high octane like that?

 

None whatsoever. There is no reason too though..........unless you just want to spend more money on fuel.

 

alright cool thanks. i think ill just go back to regular 87 then. especially with gas prices now jesus.

 

Usually you only need to run higher octane when the compression ratio is raised. If the compression is stock, no reason to use higher octane fuel other than spending more money.

-Krait

 

Other then making your motor run a tad hotter it wont hurt anything but your wallet, keep in mind the fact that the higher the octane the hotter temp it burns at so unless your motor requires it your better off running the lower octane.

 

<div class="FTQUOTE"><begin quote>keep in mind the fact that the higher the octane the hotter temp it burns at so unless your motor requires it your better off running the lower octane. </end quote></div>
This is not fact at all. As a matter of fact, this is not true.
Higher octane has nothing to do with how much heat a fuel has or how much power a fuel puts out.

 

The misnomer about octane is that the higher the rating, the better or more smoothly your car will run. In fact, premium gas can be bad for your engine if it was not designed to run at a high-octane level.

Although it may seem that the term "premium" or "high octane" implies that more energy is available, premium gas does not produce more energy than regular or mid-grade fuel. The octane grades are designed to accommodate engines with different compression ratios. <span class="FTHighlightFont">High compression engines, found in most performance cars, require a fuel that burns efficiently at a higher temperature. That's what premium fuel does, it burns hot under high compression.</span ft> In a normal engine, premium fuel does not burn completely, resulting in excess carbon build-up and carbon fouling of the spark plugs. The end result is a less efficient engine that requires tune-ups more frequently. Oh, yeah, did I mention it also wastes money?<span class="FTHighlightFont"> Compared to regular gas, high-octane gas requires higher temperature and pressure to ignite, so it can withstand higher compression without reigniting</span ft>. As such, it's less likely to result in premature ignition, and therefore prevents pinging and/or knocking

 

The fuel does not burn hotter.

The higher compression raises cylinder temps. (That is where the power comes from when you run a high compression piston) (the more heat (energy)you have in the cylinder the more power you get). When you have these high temps in the cylinder it wants to auto-ignite before the plug goes off. When this happens you get detonation. When this happens, your going to need a new piston at the least and a new engine at the most.

If it were true about higher octane fuel burning hotter; then diesel would have less energy than gas. It dosen't, diesel burns hotter than gasoline. Diesel has very low octane and very high cetane compaired to gasoline.

 

I thought high octane burned slower was the big deal.. the exploshon is slower meening it is acting on the piston longer.. using the power in the gas more efficiently in theory at lest

I actuality thought it burned cooler and that is why you have less spark knock. it dose not make the hot spots in the cylinder that causes the fuel to ignite to soon

I think diesel is like 40 octane yet have more BTU's