Premium gas for 1980 GS1000s

[jola]

Sorry to dig up an old thread, but does this octane business vary by engine displacement? I looked in my manual and they mention 89 octane but then they give a range for octane levels that are ok. I have a 450. I suppose I'll just go and experiment with 87 but I wanted to ask first.

 

[hampshirehog]

When these bikes were new they were designed to run on leaded 2 star petrol - 87 octane. Ordinary unleaded in the UK is 95 RON so you're fine in the UK and don't have to buy the more expensive super unleaded, 98 RON

 

[jola]

Thanks hampshirehog. :-D

 

[ohgoodtimes]

So if i am doing mountain riding what would be best, those hills can add some load to the engine and such, so would i want a fuel that runs cooler, but then my understanding is this would decrease power. I think i will stick with the mid grade and then throw a blower on just so altitude no longer becomes a problem......

 

[doctorgonzo]

Your compression ratio is only 9.2:1 on that engine. There is no need for higher octane gas on that engine. You only need higher octane to prevent preignition in such cases as...forced induction setups, or non-stock piston kits that increase your compression ratio.

I just saw the light on this topic recently. If you aren't getting pre-ignition, do NOT run premium gas. It will cause problems (incomplete combustion, sooty plugs) not prevent them. High octane gas is for high compression engines.

 

[Dan Ruddock]

I just saw the light on this topic recently. If you aren't getting pre-ignition, do NOT run premium gas. It will cause problems (incomplete combustion, sooty plugs) not prevent them. High octane gas is for high compression engines.

"preignition" is very rare, detonation is common and happens after the plug fires

 

[doctorgonzo]

"preignition" is very rare, detonation is common and happens after the plug fires

That as well, I was with the majority that didn't understand octane... "wait... you mean lower octane gas is MORE combustible!"

 

[jknappsax]

The GSes came in about the time unleaded gas was showing up. I remember reading a review of the 1976 GS 750 that made a point that the valves and seats were coated with stellite, so that you could run unleaded and not chew up valves, since you didn't have lead to help lubricate the valves. They also made a point that you shouldn't lap the valves, since they said it would cause premature valve wear. I agree that running regular is the way to go, though I used to run premium, but once I understood the chemistry and the physics, I relented and went regular. As many here have said, if your bike pings, then there is another issue, such as timing or excessive carbon, that needs to be addressed. Detonation will melt, hammer, and otherwise just destroy your pistons.

 

[Guest]

low octane gas no longer available

low octane gas no longer available

in many european countries you cant buy anything less than 95 octane gas, and this has been so for a number of years now
reading this thread it would follow that their gs bikes run very poorly and suffer lower performance
any thoughts?

.

 

[mac1170]

gday mate, yeh a lot of drivel on some of these, at what point do you classify an engine as being high comp, ive ran a gs11, on road and track, for 28 years, ran leaded, normal and avgas, and unleaded, all octanes, low octane unleaded is crap, put premium in, your motor will thank you for it in the long term,regards.

 

[doctorgonzo]

in many european countries you cant buy anything less than 95 octane gas, and this has been so for a number of years now
reading this thread it would follow that their gs bikes run very poorly and suffer lower performance
any thoughts?

.

A well maintained engine with good compression, hot spark, and properly jetted carbs can probably handle that higher octane and still get a complete burn with no problem. Also, they wouldn't have the other issue we have in the US with premium (93) octane gas, which is very few people buy it, so it sits in the tank at the station for months instead of being regularly cycled out from sales. A few guys with sports cars, a few rich old people, and motorcycle riders are the only people who buy it. They sell regular at 100X the rate.

 

[hampshirehog]

in many european countries you cant buy anything less than 95 octane gas, and this has been so for a number of years now
reading this thread it would follow that their gs bikes run very poorly and suffer lower performance
any thoughts?.

All it means is that we are paying more for better refined petrol (higher octane percentage, lower heptane percentage) when we don't need to. (Heptane doesn't compress very well and can spontaneously ignite under compression).

However, if I want to crank my bike up, say with a Wiseco high compession kit, I can stay running the same fuel.

 

[Guest]

All it means is that we are paying more for better refined petrol (higher octane percentage, lower heptane percentage) when we don't need to.

from what i'm reading here it seems that you also risk incomplete combustion and more deposits inside the cylinders

that said (dont know for uk, but) many european countries didnt have petrol with less than 91 octane for 30years now, that means that back then new GSs would start their life using 91 octane petrol, as that was the lowest octane petrol available

surely, japanese manufacturers were aware of this when designing their engines?

 

[doctorgonzo]

from what i'm reading here it seems that you also risk incomplete combustion and more deposits inside the cylinders

that said (dont know for uk, but) many european countries didnt have petrol with less than 91 octane for 30years now, that means that back then new GSs would start their life using 91 octane petrol, as that was the lowest octane petrol available

surely, japanese manufacturers were aware of this when designing their engines?

They were, my manual isn't handy, but I think it says 89 (lowest octane you saw then) through 95. I think the point is, premium probably isn't going to make your bike run bad, especially a well maintained, well tuned one with good compression, BUT it can exacerbate low compression and/or weak spark and make their symptoms even worse, plus the old gas problem in the US, and the fact you're paying for high octane you likely don't need. If you aren't getting pre-ignition or detonation, just no reason to spend the extra $.30 or $.40 a gallon (in the US)

 

[Guest]

thanks doc

this sums up the discussion for me nicely

btw, in nz 91 is the lowest available petrol and thats what ive been using

cheers

They were, my manual isn't handy, but I think it says 89 (lowest octane you saw then) through 95. I think the point is, premium probably isn't going to make your bike run bad, especially a well maintained, well tuned one with good compression, BUT it can exacerbate low compression and/or weak spark and make their symptoms even worse, plus the old gas problem in the US, and the fact you're paying for high octane you likely don't need. If you aren't getting pre-ignition or detonation, just no reason to spend the extra $.30 or $.40 a gallon (in the US)

 

[Steve]

in many european countries you cant buy anything less than 95 octane gas, and this has been so for a number of years now
reading this thread it would follow that their gs bikes run very poorly and suffer lower performance
any thoughts?

.

My thought on this matter is that if you read the pump (in the US), you will see that the posted octane number is an average of the Research Method and the Motor Method. I think that the European countries are using the higher number (I don't remember if it's the Research or Motor), not the lower, averaged number that we use.

For those who are in the mountain states of the US, be aware that the lowest octane available might be as low as 85. This is not a problem. With the lower oxygen content in your thinner atmosphere, you get the same combustion effect with 85 octane that we do at the lower elevations with 87. I have been able to use 85 and 86 octane when travelling in the mountains, unless we were heavily loaded and towing a trailer, then I would go to the mid-grade, usually 87 or 88.

.

 

[Dan Ruddock]

My thought on this matter is that if you read the pump (in the US), you will see that the posted octane number is an average of the Research Method and the Motor Method. I think that the European countries are using the higher number (I don't remember if it's the Research or Motor), not the lower, averaged number that we use.

For those who are in the mountain states of the US, be aware that the lowest octane available might be as low as 85. This is not a problem. With the lower oxygen content in your thinner atmosphere, you get the same combustion effect with 85 octane that we do at the lower elevations with 87. I have been able to use 85 and 86 octane when travelling in the mountains, unless we were heavily loaded and towing a trailer, then I would go to the mid-grade, usually 87 or 88.

.

Best post yet that I have seen yet on this thread. Feeding a motor more octane than it needs is a waist. Dan

 

[49er]

I'm with Brainbucket and some others on this one!
However, it really depends on whether you are running your bike as a commuter and happy with average performance, or whether you expect a bit more. If it's a commuter, go for the cheap stuff.

On my stock GS850 at 8.8-1 CR, I used to run 91 octane. The compressions were down and ranged from 110-130psi. It performed ok.

The cheapest performance upgrade is to increase the CR. Wiseco appear to limit their road ratios to 10.25-1 and I suspect, for a very good reason. At above this figure, many air cooled motors will suffer pre-ignition/detonation and overheating issues. This is compounded by the usual increase in spark advance. The solution is to run higher octane fuels.

To take advantage of the slower burnoff rate, the motor's state of tune must be quite exact, ie a strong regular spark with ideal ignition advance curve/range, correct spark plug heat range, head chamber shape and squish areas and carbs metering the fuel correctly throughout the entire rev range.

I bought an oil cooler prior to fitting the 10.5-1 pistons to my 850. I was surprised how cool the motor runs on 98. It actually runs cooler than it did in stock trim on 91. I haven't bothered to fit the cooler.
I can run 95 without detonation but it performs better on 98.
I often run 95/98 blends, as 95 is more readily available here on trips.

 

[GaThumper]

My .02 (probably .03 with inflation)

I have in the past ran premium in my bikes thinking I was treating them to a better fuel and maybe getting better performance. I now believe if it's not required due to engine design and tuning, it's better to run regular.

However the biggest thing to me came when I read (or was told) that with the high price of gas today very few people will run premium (or mid grade) resulting in possible old and contaminated gas sitting in the underground tanks for extended periods of time. Because almost everyone buys regular it's constantly being replentished, so you get fresher gas when you buy regular.

True or not, it's on my mind every time I pull up to the pumps, and I'm too worried about getting "old" gas to even think about which is better any more!

YMMV...
James <><

 

[Cajun Cycler]

Makes sense to me!