Tesco Super 99 or 97 Octane

[st5ve]

Originally Posted by Conehead

You forget to mention that on the T5, Volvo state in the handbook that they recommend using 97RON and above for MAXIMUM performance. It states that (in mine anyway) that you can use 95 RON but performance will be reduced. It does not however say it will cause a problem.
The ECU self learning theory is a Fallacy with respect to the sensors will determine the outer limits of combustion, and tell the ECU which changes the ignition and injection points to suit. i.e. it reads the knock and detonation sensors and adjusts to keep the engine within safe tolerances.( in Layman terms)
If you change the fuel you change when these sensors act because of different properties of the fuel detonating and knocking at different points. This is what is being referred to when you say the ECU adjusts, for different fuel.

This is also why different tests behave differently on different cars, because ECU's trely on other readings depending on the car, so yes a bmw M5 would behave differently to a Volvo.

This is why you use 99 Ron fuels, because you are using all the power, and why remap if you don't want more power.

There will be no problem also using 95 ron, especially for everyday use, but if an engine is making less power then you are more likely to drive it harder, if you like to drive fast, than when using 99 ron.

I tend to use whatever fuel I fancy ans whatever station I pass, and the only thing I definitley notice is it is slower on 95 ron, but as I commute a lot this is not a problem, and I know it won't reduce the engine life, regardless of what fuel I use.

Hi Conehead,

My T5 is M reg so my handbook may be slightly outdated as to the information/advice contained within. Although I did say "For the B5234T5 Volvo recommends 98 RON lead-free petrol for the best performance, but will run on any fuel with an octane rating of 91-98." So going with Volvo's information the 850 T5 can run on 91 RON, which is something I would not do, however there are certain countries that have poor quality petrol so Volvo and other car manufacturers I pressume have to a cater for those countries and detune the engine for a world wide market.

As Volvo states that 91 RON fuel can be used, why do owners suffer from detination or knocking and worst case senario bent con rods? I think Volvo would be comprimising themselves re litigation if the vehicle could not be driven spirited using a lower RON fuel after stating in their handbook you the T5 can run on such a lower rated fuel.

So another question arises, what causes the knock? A fault or failure in the sensors, ECU, fueling, timing not able to change to appropriate conditions or is it the fuel?

This is one of those subjects where the more you think you are learning something you suddenly realise more questions are being raised than answered!

[Conehead]

To answer why some owners suffer from this, you have to find out what the spec of the car is really. Perhaps it's a sensor fault, or perhaps the map they use has been taillored to what they expect?

If it has been changed from the manurfacturers spec and not been looked after then you will always have a risk of stressing engine components.
Most of the cars that appear to suffer with this have still got distributors, and would not suffer if they were full sequential injection systems.

You also need to remember that some of these cars are 15 years old with 150000 on the clock, which volvo or not is a lot of miles, and things start leaking, corroding and generally break down.

I'm not saying that you should use one type of fuel or the other, I am saying however that a standard spec car should run on normal unleaded without any of the problems, in the country that the car was designed to be used in.
But just don't expect to get 240 bhp on asda unleaded.

You also have to consider , especially after recent events, whether the fuel is quality controlled enough to worry how it would affect the car's engine.

FWIW I agree if you are going to chip your car then you like the power so why use anything but super or v-power or Ultimate? You don't have to but why would you pay for the chip and not get all it has to offer?

I'm not trying to butt in and cause/cure any arguments, I just felt that maybe for the less knowledgable I could maybe explain why different fuels effect the engine in different ways.

[bobcat]

If you read back through some of my posts ive explained what knock is and what causes it.

also heres some basic background on how you car detects knock.

On the t5 engine fitted to the 850's etc, you have 2 knock sensors fitted on the front of the block. they are nothing more than a microphone tuned to the resonance frequency of you engine. when the fuel burns you shouldnt get any noise, however when it explodes you get knock. this is like hitting the engine with a spanner, it will vibrate at its resonance frequency like a tuning fork. the amplitude of this is proportional to the amount of knock.

also knock isnt just knock, there is varying degrees of knock. imagine drawing a line on the floor by pouring out some fuel etc, imagine setting fire to it and watching the flame work its way alone (this is a normal burn), however image as it gets to the end the rest of the fuel explodes - this is knock. so depending on how much of the fuel explodes will affect the knock readings.

so as you can see from that when applied to an engine, and engine\ecu can see knock starting to happen, say for example as boost pressure is increasing.

knock normally dosent just happen suddendly and blow the engine up!!!

Originally Posted by ttacornwall

Hi Conehead,

My T5 is M reg so my handbook may be slightly outdated as to the information/advice contained within. Although I did say "For the B5234T5 Volvo recommends 98 RON lead-free petrol for the best performance, but will run on any fuel with an octane rating of 91-98." So going with Volvo's information the 850 T5 can run on 91 RON, which is something I would not do, however there are certain countries that have poor quality petrol so Volvo and other car manufacturers I pressume have to a cater for those countries and detune the engine for a world wide market.

As Volvo states that 91 RON fuel can be used, why do owners suffer from detination or knocking and worst case senario bent con rods? I think Volvo would be comprimising themselves re litigation if the vehicle could not be driven spirited using a lower RON fuel after stating in their handbook you the T5 can run on such a lower rated fuel.

So another question arises, what causes the knock? A fault or failure in the sensors, ECU, fueling, timing not able to change to appropriate conditions or is it the fuel?

This is one of those subjects where the more you think you are learning something you suddenly realise more questions are being raised than answered!

[Conehead]

Originally Posted by bobcat

knock normally dosent just happen suddendly and blow the engine up!!!

Exactly , which is why I doubt that when things go wrong inside an engine it wasn't running right in the first place and it would be wrong to blame one component or fuel.

[bb54]

hi all, only read first and last page of thread... oh how it changed
i always ran my T5 on v power but got sick of a shell ripping people off with daily price hikes.
VP is 6p a litre dearer than tesco's (96p)where i am.
iv gone back to tesco's 99 and i get an extra 10-15 miles from a £25 fill,
90 miles to £25 VP and 100-105 from T99.
for my car there is only a very slight,if any performance loss, altho i had to slacken my MBC off as i was hitting CUT constantly after setting it up for VP.
wierd how everybody has diff opinions on power and economy from T99 to VP huh.

wayne

[Conehead]

Originally Posted by bb54

hi all, only read first and last page of thread... oh how it changed
i always ran my T5 on v power but got sick of a shell ripping people off with daily price hikes.
VP is 6p a litre dearer than tesco's (96p)where i am.
iv gone back to tesco's 99 and i get an extra 10-15 miles from a £25 fill,
90 miles to £25 VP and 100-105 from T99.
for my car there is only a very slight,if any performance loss, altho i had to slacken my MBC off as i was hitting CUT constantly after setting it up for VP.
wierd how everybody has diff opinions on power and economy from T99 to VP huh.

wayne

I'm still trying to work out if there is any mileage advantage to one fuel or the other. I find it hard to say for sure when I am working different days at different times and using different routes.
Surely where and how you drive makes the biggest difference though.
And it would have to be in the same temp and weather surely to be accurate.
Which is why I thought the fuel test link for the BMW was pretty good.

I can't quite keep of the go pedal long enough to be bothered with what fuel gives the most MPG, but I do know that super makes it 'feel' faster and smoother, so I'm just enjoying being able to afford to fill my car up (just) before the global activists start on cars in their bid to save the world, and Brown ups the tax yet again.

[Engineer]

Originally Posted by ;278581

Hi Engineer,

Thanks for your input as well; I appreciate that you too are very well versed with the issues surrounding modern day engines. However, would you yourself fill your tank with 95RON before going for a track day (e.g. Marham), where there will be sustained full throttle running?

I think part of the problem here is I don`t currently see any tuner(s) guaranteeing that their ECU upgrades will run safely on 95RON fuel under all circumstances / situations (including "hard" / track usage). On the contrary, most tend to suggest using Super Unleaded (or a higher octane fuel anyway); one has gone so far as to have supposedly developed a `special` map for 95RON fuel. As a lay person in this field, I just can`t help but wonder why there is all this bother if tuned cars can run on any grade of fuel that is out there?

Hi pyaap,

Thanks for your comments, well this thread seems about dead now but was originally about fuel octane availability/usage in performance cars in general, but if its modified turbo engine answers you’re looking for then no I would not as it would put me at a disadvantage using an underpowered engine on a track day.

Regarding modified ECU’s controlling such engines though and their capability to cope with a lower octane without detonation well I guess that’s for the individual tuner to answer, the chip in the other thread obviously can’t and is sold as such, so I can’t see why it’s been used as an example.

It might also be worth considering the advancement in engine control on vehicles post ME7 as these can normally cope easily if the tuner is any good, if not then limp mode comes to mind, either way not engine destruction IMHO.

Cheers

[pigapumbu]

Originally Posted by Engineer

Hi pyaap,

Thanks for your comments, well this thread seems about dead now but was originally about fuel octane availability/usage in performance cars in general, but if its modified turbo engine answers you’re looking for then no I would not as it would put me at a disadvantage using an underpowered engine on a track day.

Regarding modified ECU’s controlling such engines though and their capability to cope with a lower octane without detonation well I guess that’s for the individual tuner to answer, the chip in the other thread obviously can’t and is sold as such, so I can’t see why it’s been used as an example.

It might also be worth considering the advancement in engine control on vehicles post ME7 as these can normally cope easily if the tuner is any good, if not then limp mode comes to mind, either way not engine destruction IMHO.

Cheers

If memory serves me right, marham is a charity event and no racing with other cars. just have fun, drive hard, pedal to the metal and enjoy. Really can't see why anyone would want to put any fuel rating higher than 95 for the extra bhp. The ECU can cope and no damage done at all. So why worry about spending more money since on track days, the fuel consumption can be heavy. Save money!!! Trust the ECU and go for it.

Funny how no tuner even those that advocate use of 95RON for hard driving are willing to put down in B&W, 95RON use is guaranteed. Yet, its blah blah this, and blah blah that. Not very convincing if you ask me for someone trying to work out if they should or should not use 95RON no matter what... thats my honest opinion of this all.

cheers