high octane fuel

[ditz]

Higher octane fuels,whist they dont burn slower, go through pre-flame changes slower than lower octane fuels. So overall time is a slower burn, hence more ignition advance and reduced knock sensitivity. They do not make more power because they burn faster.

so even if it doesnt run more power,its still smoother and cleaner then lower octane?
also if higher octane doesnt increase power why do dragsters use it and other forms of motorsport?
in actual fact sorry for my last post you dont actually want the fuel to burn too quick otherwise the air wont be burnt.
fuel is used to start the ignition of the air,air is what actually produces power,the fuel/air mixture enters the engine on the induction stroke[amazing that],inlet valve close piston raises on the compression stroke air fuel mixture gets hot from the compression then at a set point the spark plug sparks and the fuel is then ignited with the aid of the air.
the spark from the plug is the energy release which forces the piston down on the power stroke.
now a lower octane fuel will give more detonation,takes more energy to ignite [less volatile].
higher octane gives less detonation and is more volatile which means that dont need such a big energy to ignite it,
making it very advantageouse to turbo and high compression engines and also high revving engines as adding a turbo or high compression puts a bigger load on the spark to jump.
high revving engines also because they may not have time to fully recharge the ignition coil at higher rpms.

the last half of that is bang on, detonation (or pinking) is fuel igniting under compression alone (no spark) , this happens whenever compression is raised either physical compression or via forced induction,, high octane fuel has a higher resistance to pre ignition hence allowing more compression and or boost to make the power
WRC engines run the same sort of compression ratio as your average 2l NA engine and still with boost hence the reason they need the higher octane ratings, run that on cheap fuel you will end up with a big hole in each piston

 

[KrissyBufton]

People ask me why i dont come on the site no more and its because of bulls**t like this really - ive used the stuff for 8 years on race cars & road cars ( inc a 172 ) and it does make a difference.

Instead of copying and pasting from google websites and then coming on here thinking you know it all go and buy some and try it. This site is full of talk and no do

Later

the words... toys, thrown, out, of and pram spring to mind!

 

[BenR]

Higher octane fuels,whist they dont burn slower, go through pre-flame changes slower than lower octane fuels. So overall time is a slower burn, hence more ignition advance and reduced knock sensitivity. They do not make more power because they burn faster.

so even if it doesnt run more power,its still smoother and cleaner then lower octane?
also if higher octane doesnt increase power why do dragsters use it and other forms of motorsport?
in actual fact sorry for my last post you dont actually want the fuel to burn too quick otherwise the air wont be burnt.
fuel is used to start the ignition of the air,air is what actually produces power,the fuel/air mixture enters the engine on the induction stroke[amazing that],inlet valve close piston raises on the compression stroke air fuel mixture gets hot from the compression then at a set point the spark plug sparks and the fuel is then ignited with the aid of the air.
the spark from the plug is the energy release which forces the piston down on the power stroke.
now a lower octane fuel will give more detonation,takes more energy to ignite [less volatile].
higher octane gives less detonation and is more volatile which means that dont need such a big energy to ignite it,
making it very advantageouse to turbo and high compression engines and also high revving engines as adding a turbo or high compression puts a bigger load on the spark to jump.
high revving engines also because they may not have time to fully recharge the ignition coil at higher rpms.

Not really.

I didnt say they didnt make more power, i simply said they dont make more power because they burn faster, as they dont. You can make more power because you can start the ignition point at a more beneficial amount of advace to ensure that peak cylinder pressure corresponds with the correct amount of degrees ATDC depending on r/s ratio.

Fuel uses air to burn, they are not independant of eachother and fuel will consume air as required, so you cannot breakdown air or fuel burning at different points or different rates, air is used as the oxidant.

Lower octance fuel is easier to ignite than higher octane, hence its det sensitivity.

Turbos and high compression engines require more spark energy or smaller plug gaps because they have higher cylinder densities, not because of the octane. The higher density requires more voltage to ionise the gap as field strength is reduced.

 

[BenR]

the last half of that is bang on, detonation (or pinking) is fuel igniting under compression alone (no spark) , this happens whenever compression is raised either physical compression or via forced induction,, high octane fuel has a higher resistance to pre ignition hence allowing more compression and or boost to make the power
WRC engines run the same sort of compression ratio as your average 2l NA engine and still with boost hence the reason they need the higher octane ratings, run that on cheap fuel you will end up with a big hole in each piston

Detonation is not pinking, nor is it pre/auto-ignition or knock, they are all different phenomenons.

Pinking is slightly advanced ignition and the 'pink' noise you hear is the piston rattling as it goes over tdc.

Knock are 2 flame fronts colliding.

det is the pre-combustion of end gasses.

Auto-ignition is the whole hearted explosion of the entire mixture before timed ignition and is the most damaging.

The causes of each are not set in stone and combustion chamber shape, mixture homogenity, lambda, quench area and distance, bore size etc etc.

 

[cliohybrid]

so even if it doesnt run more power,its still smoother and cleaner then lower octane?
also if higher octane doesnt increase power why do dragsters use it and other forms of motorsport?
in actual fact sorry for my last post you dont actually want the fuel to burn too quick otherwise the air wont be burnt.
fuel is used to start the ignition of the air,air is what actually produces power,the fuel/air mixture enters the engine on the induction stroke[amazing that],inlet valve close piston raises on the compression stroke air fuel mixture gets hot from the compression then at a set point the spark plug sparks and the fuel is then ignited with the aid of the air.
the spark from the plug is the energy release which forces the piston down on the power stroke.
now a lower octane fuel will give more detonation,takes more energy to ignite [less volatile].
higher octane gives less detonation and is more volatile which means that dont need such a big energy to ignite it,
making it very advantageouse to turbo and high compression engines and also high revving engines as adding a turbo or high compression puts a bigger load on the spark to jump.
high revving engines also because they may not have time to fully recharge the ignition coil at higher rpms.

Not really.

I didnt say they didnt make more power, i simply said they dont make more power because they burn faster, as they dont. You can make more power because you can start the ignition point at a more beneficial amount of advace to ensure that peak cylinder pressure corresponds with the correct amount of degrees ATDC depending on r/s ratio.

Fuel uses air to burn, they are not independant of eachother and fuel will consume air as required, so you cannot breakdown air or fuel burning at different points or different rates, air is used as the oxidant.

Lower octance fuel is easier to ignite than higher octane, hence its det sensitivity.

Turbos and high compression engines require more spark energy or smaller plug gaps because they have higher cylinder densities, not because of the octane. The higher density requires more voltage to ionise the gap as field strength is reduced.

iam with you.
if you have a too higher compression ratio you can also get pre ignition?
mixture burning before timed detonation[spark plug ]? same priciple as a diesel engine.

ben about the head as per pm,i gonna get a brand new one from renault [can get cheap]
can you do all the work with just the head or do you need valves cams etc?

 

[BenR]

high compression engines can detonate simply though high temp increases as air warms up as you compress it.

I'd need the valves and bare head as a minimum.

 

[benjer172]

Have been reading this thread with interest and thought that I'd add some other points, which probably won't help but should add to the confusion lol...

Engine power is down to a number of things, the most important factor being engine design, i.e. the Clio's 4 cylinder 2 litre block ain't gonna generate a whole lot more power than when it was first designed without adding or replacing parts, turbos, superchargers, induction kits etc.

However, once you've got your engine fixed you can still do something to optimise the power by selecting the correct fuel. Unfortunately, as has been said previously, higher octane number doesn't directly result in higher power.

Petrol is a mixture of many different components. You don't just stick crude oil into a refinery and out pops some petrol. Each batch of petrol is blended at the refinery/terminal out of numerous different components. Hence each batch of 95 or 98 or 99 is different, but each will meet some basic specifications, one of which is octane number (its unlikely that a batch of petrol contains octane, its just a standard which measures knock resistance). Interstingly, the octane spec is a minimum spec, i.e. you could put 95 in your car and its actually 98! One of the critical elements of petrol, as well as octane number, is "energy density", i.e. how much energy is generated by burning a certain amount of petrol. Different components in the petrol have different energy densities. It is also typical that the higher octane number one of the components has, the higher the energy density. One of the best (and most expensive)components for increasing octane, is alkylate or reformate, both which have a slightly higher energy density than lower octane components, hence more bang for your buck.

The other interesting conundrum is ethanol, which is often blended into fuel (up to 10%) and is part of many governments "renewable energy plans" as it comes from crops rather than oil. Whlst ethanol has a high octane number, its energy density sucks compared to oil based petrol components. Hence, this will translate into a possible loss of power and/or worse fuel consumption. [Indy cars in the US that run on methanol compensate for this lack of energy density by utilising methanol's high octane number and running very high engine compression ratios.]

However, the final piece of confusion comes with premium fuels (aka super unleaded). Oil companies put a lot of research into fuels, particularly their premium fuels (v power, excellium, ultimate and the like) and its not just about increasing the octane number. The component mix may be different to improve fuel vapourisation characteristics, flame fronts, fuel burn profiles etc., the additive package will be more sophisticated, etc. Hence stick a premium fuel into a basic car and there should be an improvement in performance, but it will likely be unnoticeable unless on a rolling road. Stick it into a car designed for higher octane fuel and it should be notcieable on the road, albeit more obvious in forced induction cars (turbos and superchargers) than normally aspirated.

Hope you find this interesting.

 

[BenR]

Great point on ethanol as fuel consumption on enthanol cars such, and you have to burn alot more to make the same power.

 

[markclio2007]

http://www.youtube.com/watch?v=smLkmCRl6n0

thats some good proof and gains

 

[markclio2007]

i reckon we could see 5bhp more looking at that maybe not quite that much as turboed cars respond to everything better even air lol

 

[Neil G]

the last half of that is bang on, detonation (or pinking) is fuel igniting under compression alone (no spark) , this happens whenever compression is raised either physical compression or via forced induction,, high octane fuel has a higher resistance to pre ignition hence allowing more compression and or boost to make the power
WRC engines run the same sort of compression ratio as your average 2l NA engine and still with boost hence the reason they need the higher octane ratings, run that on cheap fuel you will end up with a big hole in each piston

Detonation is not pinking, nor is it pre/auto-ignition or knock, they are all different phenomenons.

Pinking is slightly advanced ignition and the 'pink' noise you hear is the piston rattling as it goes over tdc.

Knock are 2 flame fronts colliding.

det is the pre-combustion of end gasses.

Auto-ignition is the whole hearted explosion of the entire mixture before timed ignition and is the most damaging.

The causes of each are not set in stone and combustion chamber shape, mixture homogenity, lambda, quench area and distance, bore size etc etc.

Good summary of det etc issues

Learn't quite a bit about these issues whan i used to run an import

 

[Jim_RT]

The ECU does NOT detect higher octane fuel and adjust to take advantage of it. It detects lower octane fuel and adjusts to prevent detonation. So there's a programmed-in maximum octane level beyond which you get no further advantage.

In racing that maximum would be set very high so you could put better fuel in and get more power. But for a road car the manufacturer is going to set that maximum fairly low so that if the knock sensor fails your engine won't be destroyed. Certainly they wouldn't set it any higher than the highest octane generally available pump fuel at the time.

Since Renault put "98 octane" on the petrol cap that's what they almost certainly set that maximum to. Below that you lose power, but the engine isn't damaged. Above that you get no further power increase from the higher octane.

It may be though that since those higher octane fuels are premium products they may blend them or put additives in that make the engine run clear and smoother. But it won't produce any more power than if it was running on 98 octane. It may feel like it though.

You can get more power with more octane by upping the compression ratio. But that's not what the ECU is changing when it detects knocking. Its only changing ignition advance. If you look at how much that changes power versus how much higher octane fuel costs you find that, yes, higher octane fuel gives more fuel economy, but not in proportion to how much extra it costs.

Spot on this man!

Just read through this thread, very interesting to say the least. I've noticed people say inside the fuel cap it says "98 ron". Does the Valver need this sort of petrol, or would normal supermarket stuff be fine for it... after all, it is an old car?

Also, what you've said Gordon, I never knew any of that. So thanks! Basically higher octane will not produce more power unless the ECU is mapped to it BUT it will obviously clean the engine and give smoother running. More power though is nonsense, have I understood right?

Can I ask, as it seems a good thread to do so in, again relating to petrol for my Valver. I used to run V-Power, and she was lovely and smooth. However I recently filled back up with normal petrol and she seems very jerky. I've heard that actually, if the engine cannot take advantage of the higher octane fuel you'll be left with carbon(?) buildup in the engine? Is this true, or something along those lines?

Could this be my issue or should I infact go back to running V-Power completely?

Thanks.

 

[Se7en172]

Cool blue 106 octane - run your 172 on this and it will put a smile on your face ( £35 for 20 lts so save it for the track )

Where The hell do you get this from?
I have run mine on V-Power since owing the beast it runs fine i dont know if theres any difference because its all i have known. Is V-Power the same as Optimax? Because my shell garage only has V-Power and no fuel called Optimax.
V-Power has also gone from 96p a litre to 102p a litre in 3 months. This is crap but thats the way it is?
Now to the re-map business is my engine going to benefit more from using high octane fuels like V-Power if i get a remap?
More importantly to be honest (this is the main reason I use this fuel) Do they keep your engine cleaner? And prolong the life of your engine? Or is this all the usuall bullshit to help their product sell?

 

[Paul J]

Now we've all been educated on #RON and its effects on performance can someone explain why no one has mentioned #MON?

 

[Se7en172]

:bump:

 

[skinner]

^Not from your local forecourt!
You get it by the barrel. Best to find someone in the know if you want some or it gets expensive.

As for the eternal 95 vs 98 which makes my Clio go fastest question, you could always do some tests.

I did, and am now £150 a year better off.

The marketing guys now sell 98 as a more miles per tank fuel, which is impossible for 'us' to measure accurately. You'd have to do some very controlled tests to see if it does a couple more miles per tank.

But if you have a high performance car, or have an engine where someone got a bit carried away on the compression ratio 98 is excellent.

It does not make my 172 any faster though.

 

[skinner]

Cool blue 106 octane - run your 172 on this and it will put a smile on your face ( £35 for 20 lts so save it for the track )

Where The hell do you get this from?
I have run mine on V-Power since owing the beast it runs fine i dont know if theres any difference because its all i have known. Is V-Power the same as Optimax? Because my shell garage only has V-Power and no fuel called Optimax.
V-Power has also gone from 96p a litre to 102p a litre in 3 months. This is crap but thats the way it is?
Now to the re-map business is my engine going to benefit more from using high octane fuels like V-Power if i get a remap?
More importantly to be honest (this is the main reason I use this fuel) Do they keep your engine cleaner? And prolong the life of your engine? Or is this all the usuall bulls**t to help their product sell?

V-power is the all singing Optimax replacement.

Shell got bummed by advertising standards for their Optimax claims. You can find it somewhere on the asa website, but my link is dead.
The only one they got away with was saying it kept the back of the inlet valves cleaner.

My 172 has run on 95 for the last 35k and the inlet valves are spotless. Maybe if I run it on v-power they would look like Kim and Aggie had taken up engine rebuilds...

The remap question you would have to ask whoever did your remap. There is a potetential gain here.

 

[Se7en172]

Cheers skinner Shone a bit of light on this topic

 

[Paul J]

Seeing as it appears to have been missed ill let Wikipedia explain why MON is more important for performance than the more common RON figure..

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.
There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

 

[benjer172]

Now we've all been educated on #RON and its effects on performance can someone explain why no one has mentioned #MON?

Also, RON is the standard octane measurement in European countries and (RON + MON)/2 the standard for North America. Hence, "regular" unleaded petrol in UK with 95 octane is roughly equivalent to North American "mid grade" unleaded gasoline with octane of 91. Regular gas in the US has lower octane.

With regard to the Optimax vs. V-Power difference, the re-branding was done to bring the UK in line with the rest of Europe (along the lines of jif and cif and ulay and olay!). V-Power has 1 more octane than Optimax (99 vs. 98) and for the priviledge, Shell upped the differential between 95 and V-Power to 7p (from the 6p Optimax differential).

The main difference between oil major branded petrol stations and supermarkets is the quality and quantity of additive package in the fuel.

 

[BenR]

Now we've all been educated on #RON and its effects on performance can someone explain why no one has mentioned #MON?

http://www.cliosport.net/forum/search.php?searchid=1251447

I've mentioned it numberous times before on the same topic, but its always ignored.

 

[pete_clio]

what about BP ultimate? we dont seem to have v-power or whatever in shell garages here. just their super unleaded...unless thats the same job? and texaco premium unleaded, 97ron

 

[Peperami]

V-power is shells super mate. Bp ultimate is much of a muchness performace wise.

Have tried most fuels for motorway commutes and leisure driving, and the difference to fuel economy/ the way the car performs is amazing.

I wouldnt bother with 95, car runs rough and petrol runs out very quickly. I find mine runs best on v-power or bp ultimate.

 

[Neil G]

For christs sake we're talking Clios here not highly tuned turbo cars.