Inspired by "type of gas matters": regular in motorcycle engines?

[Fenixgoon]

My owner's manual recommends regular for my FZ6R, but the compression ratio is 12.2:1. I'm fairly certain that if a car were to have that CR, you'd definitely be required to use premium. Why the difference?

 

[JulesMaximus]

Go with what the manufacturer recommends. Spending money on higher octane fuel is just throwing your money away.

 

[Paperlantern]

Go with what the manufacturer recommends. Spending money on higher octane fuel is just throwing your money away.

Its not only throwing money away, but, why would you do something the manual doesn't specifically tell you to. It could have a detrimental effect on the engine.

As far as the question is concerned, usually motorcycle engines operate at much higher RPM, as I understand Octane rating, this would allow for less time between cylindar "uses", leaving, in turn, much less time for predetonation, making a lower octane rating okay in a smaller engine, such as a cycle.

 

[brainhulk]

i don't think engineers would recommend a fuel that would cause detonation. plus compression alone won't necessarily require premium. It's what temp is created as a result of that higher pressure. Obviously the engineers tuned the afr so that it won't detonate on regular gas

 

[LTC8K6]

Probably why you can use regular:

The 32-bit ECU controls the four-hole, two-direction, high-dynamic-range type fuel injectors for superior injection control. By delivering the precise fuel-air mixture needed for conditions, the engine can deliver great power and fuel economy.

 

[simonizor]

My manual is kind if funny when it comes to octane recommendations. It says "Use only unleaded gasoline of at least 87 pump octane (R+M/2) method or 91 octane or higher rated by the research method." It also says "Suzuki recommends that customers use alcohol free, unleaded gasoline when possible." So I use 91 because that's the only octane that I can find around here without ethanol.

 

[Fenixgoon]

Probably why you can use regular:

The 32-bit ECU controls the four-hole, two-direction, high-dynamic-range type fuel injectors for superior injection control. By delivering the precise fuel-air mixture needed for conditions, the engine can deliver great power and fuel economy.

interesting.. so why don't cars have this type of thing then? no doubt there are other considerations when making a car engine.

 

[Zenmervolt]

interesting.. so why don't cars have this type of thing then? no doubt there are other considerations when making a car engine.

Pollution control. Chances are that the motorcycle is intentionally running a bit rich, which cools the cylinders and reduces detonation. Motorcycles used to be able to get away with this as they were not subject to the same pollution control regulations as automobiles, so they didn't need to run as lean.

ZV

 

[PlasmaBomb]

As far as I am aware the design of the cylinder head/combustion chamber is the reason why motorcycle engines can run high compression ratios... well that and tight ECU control of combustion conditions.

A rough guess at some of the factors ...
Motorcycle engines tend to be oversquare - which allows for bigger valves, which should give better valve cooling (lack of hot spots for detonation).
Higher degree of swirl than car engines? Causing the intake charge to swirl more reduces the risk of detonation (two directional injectors?)
Tight ECU control/knock sensors - feedback allows the ECU to retard the ignition and prevent further knocking (assuming bad fuel)
Motorcycle engines aren't designed/expected to have to last for 200,000 miles...

Sorry I am not an engineer...
PB

 

[PlasmaBomb]

Pollution control. Chances are that the motorcycle is intentionally running a bit rich, which cools the cylinders and reduces detonation. Motorcycles used to be able to get away with this as they were not subject to the same pollution control regulations as automobiles, so they didn't need to run as lean.

ZV

Looks like you were right, at least historically... (this is an old reference).

Are motorcycles a less-polluting alternative to cars?
No, in fact, motorcycles produce more harmful emissions per mile than a
car or even a large SUV. The current federal motorcycle standard for
hydrocarbon emissions is about 90 times the hydrocarbon standard for
today’s passenger cars.

EPA 2003

http://www.epa.gov/OTAQ/regs/roadbike/420f03046.pdf

PB

 

[Zenmervolt]

Looks like you were right, at least historically... (this is an old reference).

http://www.epa.gov/OTAQ/regs/roadbike/420f03046.pdf

PB

It's still true, but the gap is rapidly closing. Many new bikes are starting to come with catalytic converters to meet CA standards. Even with the new regulations though motorcycles will still be allowed 10-20x the emissions that cars are allowed.

ZV

 

[DominionSeraph]

My manual is kind if funny when it comes to octane recommendations. It says "Use only unleaded gasoline of at least 87 pump octane (R+M/2) method or 91 octane or higher rated by the research method." It also says "Suzuki recommends that customers use alcohol free, unleaded gasoline when possible." So I use 91 because that's the only octane that I can find around here without ethanol.

Octane on every pump I've seen in the states is R+M/2. The R is the Research Octane Number, the M is the Motor Octane Number. Add 'em together and divide by two gives you the average.

 

[Fenixgoon]

My manual is kind if funny when it comes to octane recommendations. It says "Use only unleaded gasoline of at least 87 pump octane (R+M/2) method or 91 octane or higher rated by the research method." It also says "Suzuki recommends that customers use alcohol free, unleaded gasoline when possible." So I use 91 because that's the only octane that I can find around here without ethanol.

hmmm i'll have to see if that is true about premiums around me. the price difference is negligible for the tiny amount of gas that my bike uses.

 

[OILFIELDTRASH]

My 09 zx6r uses 93. Manual says minimum of 90 octane.

 

[Throckmorton]

It's still true, but the gap is rapidly closing. Many new bikes are starting to come with catalytic converters to meet CA standards. Even with the new regulations though motorcycles will still be allowed 10-20x the emissions that cars are allowed.

ZV

Why doesn't the federal gov require cats for motorcycles??

 

[Zenmervolt]

Why doesn't the federal gov require cats for motorcycles??

Technically, they don't require catalytic converters for cars. The emissions are just limited so strictly that the only way to meet the standards is to use a catalytic converter.

ZV

 

[PlasmaBomb]

It's still true, but the gap is rapidly closing. Many new bikes are starting to come with catalytic converters to meet CA standards. Even with the new regulations though motorcycles will still be allowed 10-20x the emissions that cars are allowed.

ZV

In euroland bikes have to meet Euro4 emissions, or are just about to... I will go check...

 

[Zenmervolt]

In euroland bikes have to meet Euro4 emissions, or are just about to... I will go check...

Quite possible. I was only thinking of the US market. Though, IIRC, US automotive regulations are more strict than even the most recent Euro emissions regulations. That's why US spec cars tend to have slightly lower hp ratings than their Euro counterparts.

ZV

 

[simonizor]

hmmm i'll have to see if that is true about premiums around me. the price difference is negligible for the tiny amount of gas that my bike uses.

I can only find premium without ethanol at Kwik Trip (I think Kwik Trip is WI only, though). They have a special 91 octane that is for sport and recreational vehicles with no ethanol.

 

[PlasmaBomb]

Quite possible. I was only thinking of the US market. Though, IIRC, US automotive regulations are more strict than even the most recent Euro emissions regulations. That's why US spec cars tend to have slightly lower hp ratings than their Euro counterparts.

ZV

EU cars have to confirm to EURO5 as of September 2009, so motorcycles are still lagging behind.