Pinking, knock, and octane rating query?

[snerkler]

When I took my bike for it's service last week I happened to mention that I always use super unleaded fuel in my DOHC GSA. He said to stay away from Tesco Momentum and shell vpower as the octane rating is too high (99 RON) and some customers have complained of pinking. I thought the whole purpose of higher octane was to reduce pinking and knocking?

I consulted my 'bible', "The Fundamentals of motor vehicle technology" by Hillier. This says that pinking is a result of detonation (areas of charge igniting ahead of the flame caused by the spark plug), and knocking is a result of pre-ignition (charge igniting before the spark). Surely higher octane fuels will therefore prevent both pinking and knocking, won't they?

Just to confuse me there is a sentence in my bible that says "if an engine design is prone to knocking due to detonation the engine would have to be produced with a lower compression ratios".
Surely this should read "if an engine design is prone to knocking due to pre-ignition the engine would have to be produced with lower compression ratios"?

 

[Myke Rocks]

Did it occur to you?

That the person concerned has several orifices, and statements such as he made are normally deilvered in solids form from the rearmost facing one.

Myke

 

[snerkler]

That the person concerned has several orifices, and statements such as he made are normally deilvered in solids form from the rearmost facing one.

Myke

It did, but as I'm not an expert I thought he 'should' know more than me and so questioned my own understanding

 

[Martyn H]

When I took my bike for it's service last week I happened to mention that I always use super unleaded fuel in my DOHC GSA. He said to stay away from Tesco Momentum and shell vpower as the octane rating is too high (99 RON) and some customers have complained of pinking. I thought the whole purpose of higher octane was to reduce pinking and knocking?

I think the first reply you received summed it up accurately.

I thought V Power was 98, BP Ultimate being 99, but certainly for Police 1200RT's BMW stipulate 98 or higher, presumably to cope with hard use ( & abuse) so I agree; he's talking manure.

 

[cryogenic]

I aggree when i ran on the continent with my 240 ts1 lambretta we never could guarantee the octanes at fuel stops so if any pinking occured we used octane booster and this stopped it immediatley i often found that supposed low compression heads were not at all so out with the burrett and calculations done and invariably they were too high so the dremel came out and a scalp off the compression bowl and a polish worked wonders.

 

[snerkler]

I think the first reply you received summed it up accurately.

I thought V Power was 98, BP Ultimate being 99, but certainly for Police 1200RT's BMW stipulate 98 or higher, presumably to cope with hard use ( & abuse) so I agree; he's talking manure.

I'm pretty sure vpower is 99, BP ultimate 97, Tesco Momentum 99 and total exellium (or whatever it's called) is 97.

Thanks for the replies. I'll continue to use vpower

 

[Steptoe]

Engine Knock sensors

 

[cookie]

Engine Knock sensors

FFS don't confuse him more.

shell's shareholders were dancing a jig

 

[snerkler]

FFS don't confuse him more.

shell's shareholders were dancing a jig

I'm not confused, I just disagreed with the service guy, and as I assumed he would know more than me it made me question my knowledge. But it appears my knowledge was right in the first place
And I do know what knock sensors are
Yep Shell shareholders love me as run vpower in my car and bike. Get quite a few airmiles from them though with my vpower card

 

[Myke Rocks]

On the subject of knock sensors

Since knock sensors became a normal fitment, I have never put anyting except the least expensive fuel avaliable into anything I use. OK, so maybe I lose 1 or 2 BHP at the top end, but I never use that end anyway, and it reduces running costs significantly.

Myke

 

[snerkler]

Since knock sensors became a normal fitment, I have never put anyting except the least expensive fuel avaliable into anything I use. OK, so maybe I lose 1 or 2 BHP at the top end, but I never use that end anyway, and it reduces running costs significantly.

Myke

If possible I try and stick to either Shell or BP due to them having better cleaning additives (at least they did when I last researched it)

 

[Steptoe]

If possible I try and stick to either Shell or BP due to them having better cleaning additives (at least they did when I last researched it)

Be careful of cleaning additives. They can wipe the bores clean of oil.

Remember back in the eighties, Formula shell, the wonder fuel of the time.

They had to withdraw it after a short while as it was cleaning the bores and engines were going pop.

 

[snerkler]

Be careful of cleaning additives. They can wipe the bores clean of oil.

Remember back in the eighties, Formula shell, the wonder fuel of the time.

They had to withdraw it after a short while as it was cleaning the bores and engines were going pop.

Wasn't this with leaded fuels though?

 

[JJH]

May I give my 2p worth? Using normal petrol will not cause pinking knocking pre ingiton detonation because of the knock sensors. When knocking is detected the fuel ratio is enriched and the knocking stops. I'm not sure but in extreme conditions I think that the timeing is retarded. There are certain things that lead to pinking, advanced spark, high compression ratio, grade of fuel, general design of power unit, maner of operation, air fuel mix, and carbon build up or a combination of these. In a modern 4 stroke there is very little we can adjust any more so maby look at the maner of operation. Going up a hill in too high a gear with the throtle wide open is a classic way to indudce pinking. In our modern engine electronics take over and the secondry butterfly is closed mixture enriched and the rider is none the wiser. I think. JJH

 

[Steptoe]

Wasn't this with leaded fuels though?

Oh dear oh dear.

 

[Engineer]

I have noticed a small increase in fuel economy with 98 octane fuel in my 2010GS, which is inline with BMW's handbook statement - haven't noticed any difference in power but haven't tried, would be hard to do anyway without a dyno.

The small increase in economy is offset by the extra cost of 98 octane.

 

[snerkler]

Oh dear oh dear.

Sorry but I'm not old enough to have driven/ridden in the 80's

But from what I understand leaded fuels 'coated' the internal components in lead which acts as a lubricant. I assume this helped the older engines prevent wear. If you removed this by means of a cleaner I guess this could have led to problems, and maybe why formula shell was withdrawn

New engines don't use leaded petrol they don't get the protective effects of the lead and so this effect of fuel cleaners/detergents is nulified.
Detergents are used to help prevent combustion products blocking oil passages and baking on to piston rings so surely the better the detergent, the better it is for your engine?

Please can you expand on your comment above as I've obviously missed something

 

[JJH]

the lead coated the valve seats and gave them a soft landing engines configured to use unleaded use hardend valve seats. lead damages cats (not feline) and causes brain damage in children JJH

 

[snerkler]

the lead coated the valve seats and gave them a soft landing engines configured to use unleaded use hardend valve seats. lead damages cats (not feline) and causes brain damage in children JJH

Thanks for the clarification. Still don't understand Steptoe's comment though

 

[Kenny Rodkiss]

they run the bike with unleaded to one cylider and BP ultimate to the other cylinder and show the difference.

http://youtu.be/Nkx02U8lJTg