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So I have this 1986 Suzuki GS 550 ES (as you can probably see in the pic to the left), and I've been putting the premium gas in (91 octane here I think). I have no owner's manual, so I was wondering if anone, based on that info, thinks I can switch to cheaper gas, or if I just stick with premium.

More then likely it's built for the cheap stuff.

I've heard said (here and elsewhere) that you can run some cheap stuff through and see how it runs. If you don't hear pinging and the bike runs well I think most would agree you should be cool. High octane arrests spark from combustion chamber heat - detonation. It also contains the most additives, which are not all bad. Test it out, you may be able to save money on gas.

If the bikes compretion ratio is fairly low, the cheap stuff will work. It's when you get the 10:1 and up you need the 91+ octane. Like try running 87 in a RC51 and see how well that works. +1 vote for the cheap stuff though.

To me the question is ; How much are you really going to save ? 30¢ or 40¢ at the most per tank . It is true this thread has appeared several times . I opt for Premium and always have .
That is also what we put in the new ones we build daily .
Regards, Wizzard

Wizzard wrote:To me the question is ; How much are you really going to save ? 30¢ or 40¢ at the most per tank . It is true this thread has appeared several times . I opt for Premium and always have .
That is also what we put in the new ones we build daily .
Regards, Wizzard

I'll be fair too - I use 93 octane in my bike. Do I need it? Not sure. I've run the cheap stuff with no negative effect, but I still pay the extra $.20 per gallon for the best stuff. For me I think the extra additives are good to run through my carbs. So what I said previously along with this probably is not helpful at all.

If your bike has a fairly low compression ratio, buying the higher octane may not be the best thing for it. Higher octane is less volatile, so it won't explode prematurely in higher compression engines. When used in a lower compression engine, it can lead to excess carbon deposits in the valve train due to incomplete combustion.

The best grade to use is the one that the engine was designed to use.

In the airplane world, we have a large portion of the small plane fleet that was built to run on the old 80 octane aviation gas. Now, all that is available is 100 octane. It works, but the old planes have significant problems with their valve trains because of unburnt fuel residue.

In a nutshell, higher octane is not necessarily better unless your engine is designed to burn it.

I wouldn't trust the cheap stuff in an aircooled engine. Aircooled engines are more prone to detonation than watercooled engines.

the generally accepted rule for aircooled motors is run 91 octane with any compression ratio higher than 8.5:1. And mid grade with anything higher than about 7.5:1

My 05 S50 owners manual says 87 octane is ok, my bike says it is not. With a 10:1 compression ratio I won't use anything less then 89 octane.