Author Topic: High Octane!  (Read 361 times)

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Offline Chopper75

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High Octane!
« on: May 15, 2019, 05:24:13 PM »
Been getting some popping, misfiresb and rough riding in the low range running 91 octane. I filled up with 93 today and the scoot ran amazing! Could 2 octane really make that much of a difference?

Offline Ohio HD

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Re: High Octane!
« Reply #1 on: May 15, 2019, 05:25:47 PM »
It did, right?
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Offline Chopper75

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Re: High Octane!
« Reply #2 on: May 15, 2019, 05:28:50 PM »
Just seems odd. Have to try this in my Ironhead. Been riding that much longer and have a better baseline. Never really paid much attention.

Offline Ohio HD

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Re: High Octane!
« Reply #3 on: May 15, 2019, 05:31:22 PM »
I can tell a difference in my bike with the 124" because of the compression. My 96" bike, it runs on almost anything. These are Twin Cams.
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Offline Chopper75

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Re: High Octane!
« Reply #4 on: May 15, 2019, 05:33:28 PM »
My Shovel is only an 80" so I figured it would run good on 91. Coups be bored out. Haven't had to take the top end off yet

Offline Ohio HD

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Re: High Octane!
« Reply #5 on: May 15, 2019, 05:47:33 PM »
Shovels, Pans, Iron Heads, all the older HD's with hemi style chambers and big domed pistons have less then good flame travel at combustion. So they do tend to knock, detonate, or just run rough with less quality fuel. HD went all the way down to 7:1 compression on some 80" motors to try and run the crappy fuel in the 80's.
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Offline Chopper75

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Re: High Octane!
« Reply #6 on: May 15, 2019, 06:10:46 PM »
Great bit of history right there. I'm assuming they changed over after the AMF days. Both my Shovel and Iron are AMF's. Guess it's 93 octane from here on out.

Offline Chopper75

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Re: High Octane!
« Reply #7 on: May 15, 2019, 07:15:34 PM »
Just realized that I have J&E 9.5:1 piston in the shovel...That explains it! Higher compression, higher octane. Bet it would run even better with some non-ethanol 100 octane. Way too expensive and hard to find nowadays though (NJ sucks!)

Online Burnout

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Re: High Octane!
« Reply #8 on: May 15, 2019, 09:36:06 PM »
Dual plug it, problem solved plus more power made, eliminating the need for hard to find fuel.
They don't call me Ironhead Rick just because I'm "hard headed"

Offline One4Tone

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Re: High Octane!
« Reply #9 on: May 16, 2019, 01:24:44 AM »
...you might have had some questionable fuel prior to getting the higher octane. I find temperature plays into it as well. On a hot day you might get a ping especially if your accelerating from low RPM. I allways use high test..91 octane minimum. Sometimes out in the country it's harder to find. Allways fill up in town before taking off. Years ago I used to buy Avgas (aviation fuel) from the local airport. They had 100 octane and 120 octane. You could run a full tank halfway refill with regular and still ran strong. I have a 67 chevy2, 350 cube, 11 to1 TRW's pistons. Years ago I used to get the gas from the airport occasionally...the good old days...well at least I still got the old 67...but eventually when they stopped selling the gas after 911...I had to change the heads to drop the compression...she still has the rumble...but not like before with them old double hump heads....

Offline Pete_Vit

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Re: High Octane!
« Reply #10 on: May 16, 2019, 07:52:00 AM »
never saw a difference in my 80" EVO, but my EVO Sporty wants 93 when temps get over 75* :nix:
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Offline 76shuvlinoff

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Re: High Octane!
« Reply #11 on: May 17, 2019, 02:44:23 AM »
I was always under the impression that if it doesn't pre-detonate you have zero need for higher octane and that octane didn't make power, it allows higher compression.     Truth?

 I (usually) run 93 in my TC because I've been caught in traffic jams at with over 100F coming off the pavement. Plus I can't promise I'll get quality fuel at every hole in the wall station.   I (usually) run 93 in my shovel stroker, cyl pressures were at 205 but I got it down to 185 with a cam change.  The ugly truth is I am inept at setting up a VOES and tossed it.
« Last Edit: May 17, 2019, 02:53:15 AM by 76shuvlinoff »
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Offline JW113

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Re: High Octane!
« Reply #12 on: May 17, 2019, 07:52:36 AM »
Truth. There is no more "energy" in 100 octane than there is in 87 octane. The various formulations of gasoline can change the rate of the chemical reation, i.e. "burn rate" to some degree, but the biggest difference is their self-combustion temperature. Unlike Diesel engines that use cylinder pressure/temperature to ignite the fuel and thus want as low a self-combustion temperature as possible, gasoline engines need the opposite: don't ignite until the spark plug fires.

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Online Burnout

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Re: High Octane!
« Reply #13 on: May 17, 2019, 10:01:31 PM »
I have seen increased levels of water in the fuel in the last year.

Bikes that sit over the winter, especially with the fuel valve on.
Water will settle in the carb, as the fuel evaporates, more fuel (with water in it) is admitted to the carb.
That fuel evaporates and leaves the water, and more fuel is admitted to the carb.

After a few miles of popping and banging the water in the carb got sucked out replaced with fresh fuel?
Sounds good to me...
They don't call me Ironhead Rick just because I'm "hard headed"