Why does my bike go better on 98?

[lb99]

83 GPz1100 Unitrack, fuelled up with bp98 as an experiment, I was avey surprised to notice a significant difference in smoothness and response, I am very impressed. But I am confused. The motor is hardly specced to run such a high octane, 2v fuel injected air cooled 8.7-1 compression, so hardly a high state of tune, but the difference between 91 and 98 is instantly obvious. Why?

[AllanB]

Good question. With that low compression I'd expect a lower octane to suit it.

Tried 95?

[BMWST?]

my old bmw car felt ncer using 96 at the time even though it said 91 was ok.fuel economy improved so that the cost of running was the same.It wasnt clever enough to know to adjust ignition timing,but it def felt better

[lb99]

Good question. With that low compression I'd expect a lower octane to suit it.

Tried 95?

Yup, is ok on that too. I have only pootled around town at this stage, but puddling along at 50 in top for example is much less snatchy, Although it is obviously still happier in 4th at that speed.
Certainly crisper response when you give it a handful in low gear from low rpm, maybe the ignition map has a really savage advance curve. It was the pinnacle of tech for its day

[FJRider]

Yup, is ok on that too. I have only pootled around town at this stage, but puddling along at 50 in top for example is much less snatchy, Although it is obviously still happier in 4th at that speed.
Certainly crisper response when you give it a handful in low gear from low rpm, maybe the ignition map has a really savage advance curve. It was the pinnacle of tech for its day

The bigger bangs in the cylinders do make the difference ... but how long will the motor last with those bigger bangs ... ???

[lb99]

The bigger bangs in the cylinders do make the difference ... but how long will the motor last with those bigger bangs ... ???

Thats the thing, higher octane has LESS bang than 91, so far as I understand, the higher the octane, the less volitile it is, to resist pre ignition (knock) and as far as i can understand it has less BTUs too. Higher compressions, and full on turbo engines need high octane to reduce the likelyhood of knock (or ping) so the ignition can be advanced to the most optimal position, and therefore take advantage of the available BTUs as efficiently as possible.

So WHY does my bike like it? There should be no difference

[FJRider]

... So WHY does my bike like it? There should be no difference

I had a read of few stories on higher octane fuels ... and found this ..


The benefits for fuel injected vehicles depend on the sophistication of the car's engine management system. Systems that are capable of adapting fuel and spark maps to the fuel being used are most likely to show improved performance, while vehicles with less smart systems typically won't benefit.

[HenryDorsetCase]

How do you know that it does? had it on a dyno?

because confirmation bias is a thing you know.

[caspernz]

This topic has many angles. What is the recommended octane rating for your bike? Might be 95, so using 91 makes the engine go a bit limp, whereas the 98 allows it run in full noise trim. Beyond that, the symptoms you describe may well be largely imaginary, like those swedish twins in my bed :innocent::shutup::eek:

For the purposes of your research, run a tank of Mobil synergy or whatever it's called, with the 8000 number. Basically same stuff as BP 98.

[veldthui]

My bike you can't tell the difference between 91 or 98. It works the same. Recommended is 95.

[Akzle]

calories. that's why.

[Laava]

So WHY does my bike like it? There should be no difference

Have you had your butt dyno correctly calibrated?

[robajs]

I did an experiment using 103 octane in my old ossa trials bike to improve pulling power which it did!
after riding thee trials there wasn't enough left in the tin to do another mix so poured it into my 89 r100gs
as there was only half a tank of 95 in it ....not enough to get where I wanted to go.
the bmw would pink in top at 50 kph but with around two litres of 103 octane it just pulled like a school boy .
the vp racing fuel was pricey but fun as an experiment. pre quake pioneer auto parts were in chch so it was easy to
get but now ...... who knows.:cool:

[rastuscat]

because confirmation bias is a thing you know.

Cheers. I always knew it was a thing, just didn't know what to call it.

[lb99]

Have you had your butt dyno correctly calibrated?
Yup, I do it by measuring the clench marks on the passenger seat after ridin 2 up

[Laava]

Yup, I do it by measuring the clench marks on the passenger seat after ridin 2 up

Forgive me I didn't realise you were in fact an instrumentation boffin!:lol:

[ellipsis]

...after pushing a mates bike for what seemed many leagues, once, and cursing all things fuel related, I discovered that it ran a lot better if the HT lead was connected to the plug...

[pritch]

From the dusty cobwebbed archives of my brain I seem to recall reading that the "seat of the pants" measuring equipment can't detect an improvement (or decline?) in performance of less than 10%.
Hard to imagine an improvement like that from a few extra octane. On the other hand if you like it and no kittens are harmed in the process, go for it.

[ellipsis]

. On the other hand if you like it and no kittens are harmed in the process, go for it.

...or dogs...

[AllanB]

...or dogs...

Dogs are expendable in the pursuit for more power.

[caspernz]

Dogs are expendable in the pursuit for more power.

But only if ACC isn't funding the "research" along the way :eek5::eek5:

[lb99]

From the dusty cobwebbed archives of my brain I seem to recall reading that the "seat of the pants" measuring equipment can't detect an improvement (or decline?) in performance of less than 10%.
Hard to imagine an improvement like that from a few extra octane. On the other hand if you like it and no kittens are harmed in the process, go for it.

Was running 91 when I joined the dead cat gang 😦

Burned up a bit of fuel today, highway and town, and have come to the conclusion that the bike runs smoothest at over 3000rpm, anything below that is rough and annoying, so I will use that as a benchmark, try a few different fuels and see which one makes the most difference at 50k in top (2krpm)
I doubt there is any horsepower difference, but smoother and less buzzy around town would be great

[RDJ]

I like the Placebo Effect of filling the V8 bikes and the blown ute with 98. That's enuff reason for me. Anyway I'd only waste any money saved on rates and GST on home improvements otherwise :devil2:

[neels]

As previously suggested, may be more to do with the setup of the bike being more suited to one octane rating than the other, just because it states that you can run on it doesn't mean it's running at its best.

All of my current fleet specify 95+ so don't get to experiment any more, my last car that wasn't fussy I ran on 95/98 because it actually cost less to run than on 91 when you worked out the mpg over a decent period of time.

[madandy]

perhaps the base ignition timing has been advanced from stock...a few degrees makes a noticeable difference

[Crasherfromwayback]

83 GPz1100 Unitrack, fuelled up with bp98 as an experiment, I was avey surprised to notice a significant difference in smoothness and response, I am very impressed. But I am confused. The motor is hardly specced to run such a high octane, 2v fuel injected air cooled 8.7-1 compression, so hardly a high state of tune, but the difference between 91 and 98 is instantly obvious. Why?

Is it a nice one? If so, be sure to let me know if you ever want to sell it.

[Crasherfromwayback]

. but how long will the motor last with those bigger bangs ... ???

Won't be breaking one of those engines anytime soon. Mine was taken to 1175 with much higher comp and got the shit beaten out of it for years. No problemo.

[lb99]

Is it a nice one? If so, be sure to let me know if you ever want to sell it.

https://www.kiwibiker.co.nz/forums/showthread.php/182085-Is-this-a-classic?p=1131027269#post1131027269

Theres a pic in this thread as it was when i got it, i have since repainted all of the red, new screen and seat, and new decals, looks a heap better. Will do the black parts next winter

[lb99]

Won't be breaking one of those engines anytime soon. Mine was taken to 1175 with much higher comp and got the shit beaten out of it for years. No problemo.

Was it really buzzy?

[Crasherfromwayback]

Was it really buzzy?

Yeah they do tingle a fair bit. Nothing more than a typical big four though. Make sure the engine mounts are tight.

[lb99]

Yeah they do tingle a fair bit. Nothing more than a typical big four though. Make sure the engine mounts are tight.

Yeah, gonna check that, the missus gets it worse than me, sh reckons her foot buzzes right off the peg at over 100k. Im sure the rubber mounts will be as hard as hell by now

[riffer]

It is interesting the 91 vs 98 thing. My Aprilia Tuono (RIP) did about 20km more on a tank of 98 vs 91 and seemed to run a lot smoother.

As the bike was supposed to be fine on 91, I wonder if there's some additives in 98 that clean up the combustion chamber or fuel injectors a touch?

[caspernz]

It is interesting the 91 vs 98 thing. My Aprilia Tuono (RIP) did about 20km more on a tank of 98 vs 91 and seemed to run a lot smoother.

As the bike was supposed to be fine on 91, I wonder if there's some additives in 98 that clean up the combustion chamber or fuel injectors a touch?

The 98 supplied by BP had the effect of cleaning/degumming the fuel system, or so we'd been told. All I know is that the first year or so that we were hauling 98 the product had a strong solvent type smell to it, which might explain the degumming effect. Smells different now, so not sure if that means the cleaning effect is reduced.

My dad had a bit of a stumbling/gumming issue going on in an older European car, ran a couple of tankfuls of 98 and this seemed to cure it, so go figure.

[Dave-]

Confirmation bias is why it goes better.