Harley Davidson Forums - Fuel octane question

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Fuel octane question

When I got my bike the guy that sold it to me said he uses 91 octane fuel. IIRC the compression ratio listed for my bike is 9.9. So when guys put in 10.5 or higher, what are they using for fuel? How do they deal with pinging?

Do I NEED to be using 91 octane? Seems I read 91 in the owners manual but not sure.

I always use 91 octane fuel and if I can find it no ethanol fuel. Mine runs better on it. Rule of tjumb is 10 octane points per compression level. This can be altered by aluminum heads and timing. With air cooled if you keep moving and keep top half cool and had timing set right 10 to 1 not a big deal

this gonna be a science debate, dont have my manual here, but think it says 87 or 89 in mine, not sure bout your 07........i just run the highest non ethanol i find, usually 91 or 93

91 one is the simple choice by default.
It would take a book to explain timing, combustion chambers and faults.
A caveman chamber requires more timing , a good one almost none.
My bike is a static 11.25 and runs fine on just Ron 91
So to keep this simple, not knowing anything about your bike or if you have a mechanical aptitude eardrum, default to 91

Kingglide549 summed it up pretty well.

John

Kingglide
I do have a pretty darn good mechanical backround, and axlot of it on engines, so detecting detonation comes naturally. Now on my bike, it might not be so easy, due to exhaust noise, wind noise etc.

As far as I know, mine is stock mechanically. I have always used 91 in mine, but wondered how the higher comp bikes get away with it. They cannot even sell non ethenol gas in this state, so that is a lost cause. Not sure how other CA drivers do it, unless like you said, its all in the design. That part does get deep. WhileI could not tell someone which design would be better, if explained to me, I would most likely understand.

Quote:

Originally Posted by handirifle (Post 17948949)

...snip...
As far as I know, mine is stock mechanically. I have always used 91 in mine, but wondered how the higher comp bikes get away with it. They cannot even sell non ethenol gas in this state, so that is a lost cause. Not sure how other CA drivers do it, unless like you said, its all in the design. That part does get deep. WhileI could not tell someone which design would be better, if explained to me, I would most likely understand.

Typically, those that are running the higher compressions also have different cams/headwork/piston designs and timing curves
that allow (or even require) the higher compression ratio. Hammer Performance's website has alot of good information on
what they do and why. For instance, heres a shot of my 1250 30degree reverse dome piston and my Crush ported XL1200 head.

https://i.postimg.cc/hPcK71df/IMG-0597.jpg

https://i.postimg.cc/X74Wb8sy/IMG-0535.jpg

Mine is a bit different than most people order from HammerPerf, They set my system up with 10:1 CR
and I'm using a Jackhammer 570 cam.

hth,

T.

Mine is double plug,
rechambered, (68CC)
big cam ,Dm530.
Ported , big valves
deburred,
Very small squish, >30thou
wedge pistons.(angled)
Blaah blah blah and that aint all
Its just like stock only different.
A 1000 details is truly the big difference.
https://cimg1.ibsrv.net/gimg/www.hdf...3d34be61d4.jpg

In Calif 91 is the highest top tier fuel.
Do you need to use it?
Do you ping on 89? Then yes.

FWIW with a 3 gallon fuel tank it is easy to bring octane
level up to 93/94/95 by mixing a little VR Fuel 100 octane (buy at motorcycle race shop)
to your fill up.
It is just math, Internet has ratio guides, and VR can be carried in a small canister.

One of my bikes is new, a 1200 Iron. On it and a Panhead & a stock shovel I have always and still do,use the highest octane & grade I can find. Around here "non" ethanol is hard to find, About every month or so I also give ALL my engines a shot of Techron, seems to help for me. My Engines have standard comp ratio, So I haven't used any octane booster, but I might in the new 1200 for the heck of it. I ALWAYS use the best/highest grade I can find, I believe its "false enconomy" to use lower grade. Regards "Big E"