Harley & petrol octane

[rok-the-boat]

What petrol do you use for your Evo engines in NZ - 91 or 98 octane? My engine temp is 175-210, depending on the weather. In Asia where I lived before coming here, we only had one choice. I'm running mine on 91 at the moment but it is running a little erratic, which could be the jetting being so close to sea level - plugs look fine though. I don't think it's pinging but I might try 98 next time.

[Bruiser]

What petrol do you use for your Evo engines in NZ - 91 or 98 octane?

I use only 96 and the engine runs smooth as.

Bike is:

98' FXDWG
1340
KB 9.5:1 compression pistons
EV27 Cam
Mikuni Carb
Free Breathing kit
Screaming Eagle ignition

Hope this helps.
Bruiser

[Lou Girardin]

We use 95 on our rental bikes.

[rok-the-boat]

OK, I'll try a higher octane next time I fill up. Thanks for the input.

[scumdog]

I use 91 in the lawn-mower, you trying to say it can be used on other motors??

[Lou Girardin]

I use 91 in the lawn-mower, you trying to say it can be used on other motors??

Try it in the Dyna-plow, you'll get through the back 40 much quicker.

[gammaguy]

we use 91 on our rentals.never had a problem

[xwhatsit]

You want to use anything more than 88 octane in a Hardley? Don't they run at like 6:1 compression ratios?

[Shadows]

91 is perfectly fine for Evos although it can make them protest a bit if you load them up in too high a gear. Blame the petrol if you like although that may not be the whole truth.

I use 95 or higher in mine. Just because.

[cynna]

i have only ever used 91 - havent had any reason to use 96

[Shadows]

You want to use anything more than 88 octane in a Hardley? Don't they run at like 6:1 compression ratios?

No they don't.

[scumdog]

You want to use anything more than 88 octane in a Hardley? Don't they run at like 6:1 compression ratios?

Only ones running cracked CBR heads on them.....

[davereid]

I think mine ran on bourbon.

It was always wobbling and coughing.

[xwhatsit]

Only ones running cracked CBR heads on them.....

Lol!! Green rep awarded

[xwhatsit]

But seriously though, notwithstanding poor Honda cylinder heads with cracks , as near as I can work out the Evo engine has about an 8.8-8.9:1 compression ratio. Now, according to everything I've read, octane rating is purely a rating to ascertain the anti-compression-ignition properties of a given fuel. Now, I understand that some cylinder head designs are more susceptible to compression-ignition (or detonation) than others -- I just recently read some stuff about cages with Ricardo heads, with `squish points' and stuff like that, designed to avoid detonation -- but the biggest factor in detonation is the amount of compression the charge is under.

So if a CB250RR with an 11.5:1 compression ratio can run 91, why can't an Evo with an 8.9:1 compression ratio?