Which Octane?

[Motu]

Why do you call it pinking?
.

That's the English term,and us old farts always called it that.More of a pink,or plink sound than ping,which sort of implies ringing,which is not the case...pink is a dead sound....follow?

Back in the days when we actually tuned engines,final timing adjustment was done listening to pinking,just a tad of pinking pulling from 20mph in top gear.

[MSTRS:Me]

That's the English term,and us old farts always called it that.More of a pink,or plink sound than ping,which sort of implies ringing,which is not the case...pink is a dead sound....follow?

Back in the days when we actually tuned engines,final timing adjustment was done listening to pinking,just a tad of pinking pulling from 20mph in top gear.

WE gotta stick together against the yunguns eh??

[The Stranger:Me]

...pink is a dead sound....follow?

Get with the times old man.
Pink don't sound too bad at all really, she looks ok for that matter too.

[The_Dover]

i think she's getting fat.

lay of the high octane diet Pink you porker.

[sugilite:Me]

My experience is that if you run a motor on a higher octane gas than it is designed/tuned you will lose low end power. When I was racing the ZX9R Superbike, It was a running very high compression. When I ran it on straight race gas there was a noticeable loss of low end power, so I started running 70% race gas 30% 91 and hello low end power again, thanks to 91's faster burn time. It was even more noticeable when I ran straight av gas in my KX500 motard bike, as in where the hell has the low end power gone? No amount of jetting changes seemed to recover it. Thank goodness the old 70/30 ratio worked on that too.

I noticed the 10 was designed to run on 90 octane or higher, I could not tell the difference between 91 and 98, though now we run a race ECU, I run 98 all the time now.
I tried 91, 95, 96 and 98 in the 750 and settled on 91, and as mentioned won the championship running 91.
Believe me when I say I rung that poor bikes neck and I would have noticed any slight horsepower increase that higher octane "may" have given me.

Long story short, just run the bloody things on what the manufacture specifies, no point going higher unless you tune for it.

BTW, the "race" gas you get from gas stations near the race tracks is just stale aviation fuel the airports have dumped, thus the octane level will never be consistent.

[vtec]

I just won the Streetstock racing Series on my CBR250RR running 91 octane. The bike is designed for it, and despite being a screamin' 250, it's compression ratio isn't insanely high. Another point to consider, for the high revving bikes. A faster burn (lower octane) should mean that you get more power... You want to run the lowest octane you can without having to retard your engine to avoid pinking, as that will usually give you the most power... Just check the manufacturer's specifications.

When I used to run 98, it didn't run as well lower in the rev range, used to miss a bit... it seemed to make the bike run a little rich... Botany Honda mechanic recommended that I only run it on '91.

Each bike is different though... all depends on design. I know that my Honda Prelude needs 98, as it can develop a knock if run on 91.

[Sketchy_Racer]

Yep what Vtec and Sugilte said.

I was Came second in Streetstock (behind Vtec) On my KR150.

I ran it on 91, as it was cheaper. and 96,98 made no difference.

Most streetbikes are tuned for crap fuel, so there is no point wasting money on expensive fuel if it does nothing for the bike.

[xsive-rider]

91 my ass... sluggish like a bastard on 91, won't touch the stuff... 95 is ok, but I'll run it on 98 whenever possible.

Seriously, run it on a tank of 98, then try stepping down to 91, it's just painful.

i reckon!
you may as well put water in there than use that 91 shit, good for jappa cages.

[onearmedbandit]

Despite what 3 people who race have said, along with all the other info provided?

[Jantar]

I have kept a careful record of fuel use on my DL1000 ever since new. I started doing it as part of Jim2's fuel comparisom re the new Shell fuel. What I have found is that there is not a noticeable power difference between 91 and 95 in any brand of fuel, but I am getting close to 8% better fuel mileage from 95 than from 91 octane. That is considerably better than the price difference.

I can't say that this would be the same on any other bike, so all I can recommend is that each rider keep their own records and see if there is any difference for their own bike.

[Grahameeboy]

Get with the times old man.
Pink don't sound too bad at all really, she looks ok for that matter too.

We get pinking in Devonport!!

[Bonez]

Many would disagree however. Is that from personal experience CS? I know guys who run 91 in their sports bikes with no dramas. Not me however, my bike prefers 96.

My old GSX750EX hates 91 too, pinks like hell. Reading the old write ups indicates this was a common thing with them. Runs sweet on 95. But I feel with a timing tweek will sort out the pinking to run on 91.

[The Stranger:Me]

Ok, ok, I know the subject is done to death.
But here I go again anyway.

As I commented, the gains (torque and fuel economy) I experienced were in low to mid range. Somehow I suspect that if you are winning races you are not spending a lot of time in that area. I am sure I will be corrected if I am wrong there.

As a matter of interest, did you try runing 98 and advancing the timing a couple of degrees. If you are after more performance I would think this would be worth a try.

I aren't trying to say that all vehicles will benefit from higher octane, indeed my SS commodore runs better on 91 right through the rev range. But I am trying to say it is worth evaluating with an open mind, and you should not write it off just because of the higher initial purchase price.

[sugilite:Me]

As I commented, the gains (torque and fuel economy) I experienced were in low to mid range. Somehow I suspect that if you are winning races you are not spending a lot of time in that area. I am sure I will be corrected if I am wrong there.

I'm not sure you are are addressing directly, but as I'm one of the racers I'll reply

I do run in the lower rev ranges on some corners and I also tend to be a gear higher than most through the corners (must be something to do with my ride style) so yeah, I really do notice any drops in power in the lower ranges.
Most of my testing was done on my private test track that has everything from tightening radius hairpins to 2 km straights.

I did make timing adjustments for my KX500, but had to as I had to run the 70/30 av gas/91 mixture so it would not grenade on long straights found on road race tracks....

As mentioned in an earlier post, unless you tune for it, stick to the recommendations of the manufacturer.

[sugilite:Me]

I finally tracked down a article i did for supermoto.co.nz
My 500 had blown up and i went to the master of octane info, Robert Taylor.
heres the article...

The other Weekend my KX500 came to a grinding halt whilst racing at Manfield. After a top end tear down, the electrosil was found to have flaked off the barrel. Not good as I had not long just got it back from the platers. Turns out it was due to detonation. I was running BP Ultimate 98, so I was surprised to find that it had been detonating that badly. A respected motorcycle figure did some research on BP98 by contacting BP themselves. Guess what, you can forget NZ petrol octane ratings as they are quite misleading. Read on....

Here are some of the details supplied to me on the matter. (In italics)
The specs for BP98 are alarming. I don't know whether you are aware of same but all "pump" petrols (98 is a 'pump' petrol as such) have their octane ratings listed as the RON or research octane method. This is a little misleading and is not the information that racers really require.
Looking at the attached spec sheet the MON or motor octane rating of this fuel is in fact only 84. The MON number is always lower but not by such a huge amount.

Note that as a comparison the MON number of 91' pump petrol is 82, not a lot different.
Would you run your motor on straight 91'?
The respective anti knock index ratings are also not that encouraging.
Note that although the spec sheet is written / itemized a little differently for No. 1 / Avgas, but in fact the RON number is typically within 105 - 110
even though they don't rate Avgas in this way. The MON number is 100 or more, which is exactly the "territory" you need for your motor.
Note that BP "Ultimate 98" is an "Environmental" fuel, it is not marketed as a racing fuel as such and has low benzene count.

So there you go
folks, always be very aware of the octane sensitivity of your racing 2 stroke. Some motors may run happily on pump fuels but many are very sensitive and can detonate quite readily due to a whole host of variables.
Many of the late model highly tuned 2 stroke MX based bikes require at least
a 50% concentration of Avgas and 50% 96. Those most sensitive to detonation will require an even higher concentration and so on. As Avgas has a slower burn speed it is popular to use "cocktailed" with pump fuel to raise the burn speed for decent
engine response.

The flip side is that with very high concentrations of Avgas, reed petal life becomes shortened."

The other factor to be aware of is that in the autumn months fuel companies change the volatility of their fuel for easier starting in cold weather. "The fire lights easier" and burns more rapidly. This is no problem for your average passenger car, which accounts for 99% of the fuel company's market.
However, this can very often can be detrimental to a highly tuned racing motor, engine problems can suddenly appear in the
autumn months that weren't there during the warmer months.

By law of averages we are just a small minority and a relatively small annoyance to fuel companies who are only concerned about a bigger picture.
Nothing is ever as simple as it seems......................


I find it interesting that when approached at a technical level, BP say they market 98 as an environmental fuel, but in actuality, looking at the adverts for it at their stations, they seem to market it as a "fuel for performance vehicles"

Oh well, time for time to go and have a good cry and work my ass off to get some $$$ to do it all over again.

Sugilite out!