So are you suggesting a lower octane fuel ignites and burns at a lower temperature and thus produces lower engine/head/exhaust pipe temperatures too???

Maybe that's what I'm noticing.

 

Nope I guess not, I guess you've never seen a gas motor converted to run diesel? It was a way to demonstate that you don't have to have spark to get low octane fuel to explode/ignite only higher compression. Seems I struck a nerve with you, so I'll just leave it at that.

 

So true! Smoke out the street, pics please!!!

 

That's a good question. One which I don't know the answer to.

Lower octane requires less air to burn completely and would combust better under normal conditions. Thus, creating more horsepower. Under normal conditions, 93 octane fuel very well may not fully combust. If your vehicle is not engineered to run high octane fuel then running 93 can actually harm the engine.

Based on that conclusion, I think it would be safe to assume that running 87, if you don't get any knocking, is just plain better for your motor in every single way imaginable.

My bike calls for 91 octane. We don't have that here. 89 or 93, those are the choices. It is freakin hot down here so maybe I'll run 93 in the summer and 89 in the winter, provided I get no knocking.

 

Here's a video of my silver Charger at the track right after I bought it. Two good runs I made in the video. My second run has a better burnout then my 1st run. They're in water that's sprayed on the track so there's not a lot of smoke.

Still fun though

http://www.youtube.com/watch?v=0qgEGFxTfDw

 

Good old bracket racing,, thanks for sharing. Hijack over back to your regular scheduled 87 fuel post.

 

Not sure I even wanna touch this bee hive. Looks like there is plenty of 'detonation' going on already.

Several things can cause detonation. The uncontrolled burn of the AF mixture, read that EXPLOSION. Not good.
Pre-ignition is one of the things.
Pressure is another. Read that, 'compression'
That is also what allows John's diesel tractor to fire with that 'syrup' being injected into it. Heat of Compression.

The TPV equation. Temp, Press, Volume. For this scenario, it is T= P/V. The piston goes up, Volume decreases, Pressure increases, Temp goes WAY UP.
Touch the top of your air compressor when it gets done filling your air tank. That's "Heat of compression"

Octane 'controls' the flame travel in the AF mixture. The higher the octane, the higher the pressure needed to ignite it. Thus, use a higher octane fuel in a higher compression engine, to prevent it from igniting, due to heat of compression.
I do not remember the 2 ingredients used to determine octane, but the octane # is a percentage of one of those ingredients.
And as mentioned, higher octane does not translate to higher power.
You have to run whatever octane will prevent detonation. If 87 runs, then run 87. If it is knocking or pinging, up the octane.

You have prob'ly heard pre-ignition, if you have ever shut off the ignition, and the engine will continue to run on. That's caused by pre-ignition.
Will it run cooler? I am not 100% sure.

I have never tried this on a 'new' HD, but on cars, you can test the 'knock sensor' by rapping on the manifold next to the sensor and observe what the timing does. If I remember, I'll try that next time I have one near.

We just had a thread over in Sporty section, guy complaining of a 'shudder'. He posted the speeds he was sensing the shudder. It was 'detonation', from lugging the motor. He was basically riding his Sporty like his Big Twin. They won't 'lug' like a BT. Lugging causes very high pressures in the cylinder, thus the 'detonation'.
It will tear a motor up if you keep doing it.

Okay, go ahead, 'FLAME travel' away.

 

I think fuel quality around the counrty varys and maybe more so with the summer blends.Ethanol mixing is common depending on station/area. I still feel two efi maps are sometime needed lately. If the bike runs good on regular or mid brand,use it.The difference in performance might be seen on a dyno un unlikely for most owners on the street. A better tune will allow you the use of cheaper blends,an oil cooler should help with detonation chances.Some of those octane additives are hell on fuel parts,plugs.

 

BUT, as your elevation increases, the need for higher octane decreases. That's why in cities at higher elevations premium fuel tends to be 91 octane while at sea level, premium fuel is 93 octane.

 

Last month's American Iron had the first of a series of articles by Donny Peterson, which has most of the facts concering what's being debated here about octane, detonation, heat, etc. The November issue that came today has the second of the series.