Necessary Octane For Your Bike?

[mototireguy]

There's some banter on the 600rr.net forum regarding the use or necessity of higher octane fuel on their bikes. Just thought I would import the discussion here for the heck of it.

I think the octane choices for our motorcycles depends on the compression ratio of the engine. Higher compression numbers are more likely to cause the air-fuel charge to prematurely detonate (ping) under high output conditions before the spark fires. Higher octane fuels resist this premature detonation. What is the compression ratio of your engine? Some examples...

Honda Spirit 9.0:1
Honda 919 10.8:1
Honda RC51 10.8:1
Honda CBR1000RR 11.9:1
Honda CBR600RR 12.0:1

You can probably get away with 87 octane in the Honda Spirit. Mid-grade for the 919/RC51. Probably stick with +91 octate for the RR bikes.

Race gas +100 octanes contains higher levels of oxygenates (commonly MTBE) which offer additional power and resistance to detonation. Really only needed for race applications in extra high compression engines.

http://www.racegas.com/fuelspecs/sunocogtunleadedplus.htm

 

[Silent]

EX250 12.4:1
Recomended 87 Octane.

I've been running 87 for 7k and not a single problem. I know people with over 80k on 87 (EX250's) without problems.

 

[XXshawnXX]

what about an f2 i am runnin 89 and it seems to run well, with no probs

 

[aminalmutha]

The last time I sat on an RC51, there was a sticker on the tank proclaiming "use 92 octane or higher" or something to that effect. It's not only compression ratio that determines what octane rating is best. The size of the cylinder has a lot to do with it as well.

In a four banger, you're more likely to get even, complete burn since the cylinder is smaller than on a comparably sized twin. I think that temperatures are probably a little more evenly distributed in a relatively smaller combutstion chamber.

Cooling methods and ambient air temps can affect appropriate octane ratings as well. Air-cooled bikes tend to run a bit hotter than water cooled bikes, particularly in hot weather.

There are a lot of other factors as well, such as how well the fuel is delivered to the cylinder, how well it is metered, combustion chamber design, etc.

I'd go by what the mfg. says, if anything.

 

[Valgar]

Vulcan 500LTD 10.2:1 87 octane
Kawi Ninja 636 12.9:1 91+ octane
ZR-7S 9.5:1 anything that burns or 87 octane
Z750S 11.3:1 87 octane
GS500 9.0:1 87 octane or any mud that is handy

 

[OaklandF4i]

I've always thought that if the engine wasnt pinging or doing anything else abnormal - using the lower grade was probably ok.

I use regular in my F4i and have not noticed any issues after 35K miles. My Landrover says to use premium, but honestly getting 10mpg and using premium doesnt happen with me. Again, I have not noticed any ill effects. But I dont wrench proffesionally.

I would be curious to hear what the pro wrenchs have to say. Especially if there are other effects that are not noticiable.

 

[xgambit]

mine likes 151. especially with coke and a squeeze of lime.

 

[cvlighthouse]

I have the 600rr and a Arata full system and DK's PCIII map. I run a mixture of 91 and VP race fuel. I like it. I like it a lot. There is more pep. Engine runs cleaner. The black carbon build up on the end of my pipe has been replaced by a nice white color. BTW the owners manual for the 600rr says to use 87.

 

[cleoent]

i just use 91 on my 636. I mean even if i used 87 or 89 at most i would save 20c a gallon (if i used 87) or 80c a fillup. 80c x 4 weeks per month= $3.20. For .80c a week in savings, or 41.60 a year in savings, it's not worth the risk.

 

[Joebar4000]

It's not as simple as compression ratio.

Smaller pistons can get away with lower octane fuel because there is simply less time for detonation to occur.

Also, you're looking at static compression ratio - the ratio of swept volume to compressed volume.

This doesn't take into account when the valves open/close, which has a dramatic effect on that ratio.

It also doesn't take into account air box volume, port size etc. etc.

It's WAY WAY more complex than just looking at static compressin ratios or bore size.

Go with what the manufacturer recommends, or if you have access to a dyno, whatever makes the most power.

Too high an octane - LESS power - the chains aren't broken apart and you get incomplete combustion. This does mean the engine runs cooler, so it is safer to run higher octane fuels than risking detonation. But it's not best for power.

 

[shadowcat]

I hate to crosspost, but what I said in the other thread is valid here as well:

It's simple. Run the gas your manual tells you to run, if you are running a stock engine. All the octane rating does is tell you what resistance the grade of gas has to premature detonation, aka "knock". That's it. Nothing else.

If you've tuned for a more aggressive fuel map, etc., then run whatever grade keeps your engine from prematurely detonating the air/gas mixture in the cylinder as the piston compresses it. If you are running a stock engine that is rated for 87, and you are buying a higher grade of gas, you are wasting money.

--

see.. here's the thing.. it's not just about how much compression your engine is running.. it's also about when the spark is ignited, what the air/fuel mixture is, etc. Premature detonation happens when there the air/fuel mixture is exposed to more heat and pressure than it can handle. Here's a good page that explains it all: http://www.unionbayracing.com/fuels.html . A few good things to point out:

1) Higher octane fuels are MORE RESISTENT to ignition. In other words, they burn slower.

2) Using more octane than you need will not help power. In fact, the slower burn rate will actually cause you to lose some power.

The Honda engineers know what they are doing. The bike is out of the factory with non-aggressive air-fuel map, that does not require any more pre-det resistance than 87 octane provides. People who aggressively tune their engines for higher performance will need higher octane, and race-prepped engines need race fuel to run properly without pre-det.

Unless your bike has seriously modified air-fuel maps and very aggressive tuning, you REALLY don't need anything more than what the factory specs call for.

 

[lefty]

Yesterday I paid $2.89/gallon for my 91 octane.

Hell, I may have to start riding my bicycle to the liquor store!!!!

 

[faz]

In some engines, it makes a difference in the performance. My 2001 Miata performs much better with 91 octane, vs. 87 or 89, since it actually delays spark if it detects detonation. My other car also asks for 91 octane, and it idles a lot nicer with 91 than others.

On all my bikes, ninja 250, honda magna, f4i, superhawk, nighthawk, katana... I have always used 87 and they all performed well, sometimes better than with 91.

 

[2DUCKS]

I used to Run 91 as the manufacturer suggested, but have switched to running 87 without much problems.

 

[cleoent]

In some engines, it makes a difference in the performance. My 2001 Miata performs much better with 91 octane, vs. 87 or 89, since it actually delays spark if it detects detonation. My other car also asks for 91 octane, and it idles a lot nicer with 91 than others.

On all my bikes, ninja 250, honda magna, f4i, superhawk, nighthawk, katana... I have always used 87 and they all performed well, sometimes better than with 91.

your problem is not with the gas, it's that you have a miata

j/k

 

[cvlighthouse]

This is what I mix the 91 pump gas with. 1/2 and 1/2

VP-110
Not your "standard" 110! Highest rated MON of any 110 fuel on the market. Formulated for use in naturally aspirated engines with CRs up to 14:1. Works well in 2-strokes. Good lower cost alternative.

• Color: Purple
• MON: 107, RON 113, R+M/2 = 110
• Specific Gravity: .720-.735 @ 60° F

http://www.vpracingfuels.com/vp_01_fuels.html?mgiToken=0C15B7C862B785C1E7

http://www.lipertracing.com/catalog...id=97&osCsid=1cc0cc7e4a7ddf2ee79470d49b77bbf3

 

[espitbullpup]

I have the 600rr and a Arata full system and DK's PCIII map. I run a mixture of 91 and VP race fuel. I like it. I like it a lot. There is more pep. Engine runs cleaner. The black carbon build up on the end of my pipe has been replaced by a nice white color. BTW the owners manual for the 600rr says to use 87.

I think it says use supreme 91 or was it 92

 

[Dar25]

I use 87 almost always on my 600RR, sometimes 89.

You really dont need a higher octane gasoline unless you experience knocking.

I run my acura on 89 even tho reccomended is 91. No problems either. If anything it seems more responsive with lower octane fuel.

 

[MtnRacer]

The higher the octane, the slower the fuel burns. The slower the fuel burns, the less power you make. Octane doesn't have anything with quality of the fuel. Unless the bike's modified, use whatever the owner's manual says.

Steve

 

[cvlighthouse]

BTW the owners manual for the 600rr says to use 87. Yup It does.

Pump fuel is crap. It's dirty and for that reason I dilute it with clean race fuel.