Types of Fuel (octane)

Puddleglum · 08-26-2009, 11:58 AM

Rode for a while the other day and am really liking my new bike. I stopped to fill up and thought........what the heck, I'll put premium in it.

Well now the FI light is on, and I'm kind of putting two and two together. I would like to check codes, but am not really sure how to do that.

I also need to find the best place to get a manual. Is there a website that you can download a manual from?

Diamondback · 08-26-2009, 12:23 PM

RC51.info has the service manual online in downloadable format. I run 93 octane in mine and have had no problems.

jeffro17 · 08-26-2009, 3:08 PM

I was running 93 in mine when I first got it. Then started to get alot of backfire. So I went for 93 to 89, it has ran alot better since. My best guess is the 93 sits in a tank alot longer than the other two brands and running that fuel in small motor compared to a car, just makes the engine run like crap??.!!

Diamondback · 08-26-2009, 5:10 PM

Quote:

Originally Posted by jeffro17

I was running 93 in mine when I first got it. Then started to get alot of backfire. So I went for 93 to 89, it has ran alot better since. My best guess is the 93 sits in a tank alot longer than the other two brands and running that fuel in small motor compared to a car, just makes the engine run like crap??.!!

Backfires or popping on deceleration? Popping may be caused by the PAIR valves on the bike. Popping on decel may also indicate a lean condition. What mods are on the bike? Do you have the bike remapped?

As far as the fuel goes, I don't think the 93 would sit long enough to go bad, at least not where I normally buy my fuel.

Nvp1986 · 08-27-2009, 8:03 AM

Hmm I have always run 93 octane in it and I have never had any problems?? Out of curiosity what does the owners manual recommend?

zerogara · 08-28-2009, 4:56 AM

Octane rating has more to do with compression and not size of engine, and therefore ignition timing. Whether it is a 50cc cylinder or a 750cc cylinder it only matters in quantity. You just don;t want fuel mixture to preignite before ignition fires. If you look at the compression on the RCs it has the lowest of all current sportbikes out there. I don't know about the Buell but who cares.
Even sport touring bikes these days have >12:1 while the RC has 10.8:1. I think the HRC kit pistons are 12.5:1, which is what Ducati was running at the time.
Also octane rating is not universal, ever since unleaded gas came out different regions use different standards. In many places in Europe regular unleaded is 95' while premium is 98-100 For the US these numbers are for race gas. So I imagine the 87 in US is close to 93 in Europe, while the 95 like Sunoco had for years is close to the European 98.
Most of that octane rating is related to additives that are very volatile. Some of the reports that I've read is that the longer the gas vents the lower the octane rating goes of the premium gas. So eventually your premium will turn back to regular.

As I have never noticed a problem with pre-ignition on the RC and I think the compression is low enough I have used regular on it. I did so after I read in the Rogue site that it made no difference while many engines made more hp in the dyno with regular.

SubSailor · 08-28-2009, 9:42 PM

Quote:

Originally Posted by zerogara

Octane rating has more to do with compression and not size of engine, and therefore ignition timing. Whether it is a 50cc cylinder or a 750cc cylinder it only matters in quantity. You just don;t want fuel mixture to preignite before ignition fires. If you look at the compression on the RCs it has the lowest of all current sportbikes out there. I don't know about the Buell but who cares.
Even sport touring bikes these days have >12:1 while the RC has 10.8:1. I think the HRC kit pistons are 12.5:1, which is what Ducati was running at the time.
Also octane rating is not universal, ever since unleaded gas came out different regions use different standards. In many places in Europe regular unleaded is 95' while premium is 98-100 For the US these numbers are for race gas. So I imagine the 87 in US is close to 93 in Europe, while the 95 like Sunoco had for years is close to the European 98.
Most of that octane rating is related to additives that are very volatile. Some of the reports that I've read is that the longer the gas vents the lower the octane rating goes of the premium gas. So eventually your premium will turn back to regular.

As I have never noticed a problem with pre-ignition on the RC and I think the compression is low enough I have used regular on it. I did so after I read in the Rogue site that it made no difference while many engines made more hp in the dyno with regular.

FYI
Owners manual recommends 91 octane or better.
Buell XB series bikes have 10.5:1 compression.
HRC heads had smaller volume than normal RC51 heads.
So 12.8:1 HRC pistons in regular RC51 equates out to around 11.8:1.

UKRC51 · 08-29-2009, 9:38 AM

Hi Jeffro17,

If you geting a lot of popping on deceleration you might have a small exhaust leak, and what happens is that additional air gets drawn into the exhaust pipe causing any unburnt fuel/gases to light off causing a popping/backfire noise.

Gary

Picante · 08-31-2009, 2:57 AM

My owner's manual says 92 (or higher)

zerogara · 08-31-2009, 3:15 AM

Here is a table from Wikipedia octane_rating article

Octane rating - Wikipedia, the free encyclopedia

So when you talk about octane rating you have to state which rating you are using.
Shell V-Power Race and BP Ultimate 100 in Europe have a rating of 100 but it is not the same scale as in the US

RC51.org the truth about race fuel page

In testing various grades of pump gas I consistently found that 87 octane fuel makes 1-2 more horsepower than those exact same bikes ran on Premium 93 octane. We tested five liter class motorcycles (97 CBR900RR, 02 Honda 919, 2000 RC51, 2000 GSXR750 & an 02 R1) & only the R1 seemed unaffected by the octane of the fuel. Now I am certainly not going to tell you to run less than the recommended octane (92) in your RC51 as the specific needs of the motor dictate that a higher octane fuel is needed, but the results are blatant in that more octane does not mean more power.

Suum Cuique · 09-16-2009, 8:35 PM

I always presumed higher octane fuel would be better for a high performance engine but I don't recall anyone ever telling me that they left someone on the far horizon cos they had a tank of premium. I'll probably still get it if it's there though.

Nvp1986 · 09-16-2009, 8:52 PM

I know for a fact that the same exact bike on the lower octane will make more power. The only problem is that if you run a bike on an octane lower than it is tuned to run with the fuel may explode due to hot spots on the piston while the piston is still on the way up and that is called detonation. Eventually it can either grenade the piston or rod or even melt the side of the piston. The entire idea of higher octane is that the fuel is physically harder to burn. Thus it is harder to preignite the gas before the spark plug fires off. That is why it prevents detonation from occuring.

Usually however engines are tuned more aggresively and thus they require premium gas and then in turn they make more power using the premium gas than they could safely make on a lower octane fuel. This becomes especially important in high compression engines and forced induction engines.

kewjr · 09-16-2009, 9:04 PM

91 and up always!! seems like it likes the 93 better

zerogara · 09-16-2009, 11:22 PM

Great post Nvp!
The most hp can be achieved with the lowest octane you can safely run without pre-ignition and detonation.
Running 115 race gas on a 67 Honda CL175 will only take hp away and money off your pocket. If someone has had evidence of pre-ignition/detonation on an RC running on the street I'd like to hear that evidence.

Quote:

Originally Posted by Nvp1986

Thus it is harder to preignite the gas before the spark plug fires off. That is why it prevents detonation from occuring.