I have just filled up with Sainsbury's Super Unleaded 97 Octane. (We do not have Shell or BP garages nearby btw to buy their super dooper fuels.)

How does the car sense that it has a higher octane fuel and when does the adjusted timing or whatever start to take effect? And ditto when I go back to the 95 Octane stuff.My fuel flap says 95 Octane minimum so I know from the manual that better mpg and more power may result.

It's the technicalities I'm interested in really.

Knock sensors

Google "knock sensor".

From a safe starting point, the ECU continuously tries to advance the ignition timing a little, 'listening' (literally) for feedback from the knock sensor(s) that it has gone too far, then backs it off a bit. Rinse and repeat.

If will take approx. three full tanks to flush any lower grade out & for the ECU to fully adapt..

 

ie, run car until fuel gauge is in red, fill up fully with super unleaded, run car until fuel gauge is way in the red, fill up fully..etc..

 

Knock sensors & variable camshafts....The 1.4TSI 122/125PS has one variable camshaft...the 140/150PS versions have two variable camshafts...& can really make use of the better petrol..

 

Also cleaning packages in the super stuff is way better than standard fuels, so this stops the ERG systems etc. clogging up as easily...

Worth saying that if at any time you used a lower grade fuel it will fully retard any advances made in the timing to avoid knock and you will be back to square one. So if your committed to getting the benefits of higher octane fuel you need to stick with it. 

Oh well,

I just tend to run the super every few tankful's for the cleaning benefits so I may not get the other improvements. I'll try a few tanks of 97 octane- got a few long distance runs coming up. And on the 150psi the EGR system is internal, from the TSI data I've seen. The exhaust valves can shut early under some conditions to retain some exhaust gasses rather than it going out then coming back into the engine via a valve. 

Edited 17 April, 20179 yr by gregoir

I run 99 ron constantly, it should be obvious to anyone looking at my fuelly !!!

1 hour ago, MrAdamwood said:

Worth saying that if at any time you used a lower grade fuel it will fully retard any advances made in the timing to avoid knock and you will be back to square one. So if your committed to getting the benefits of higher octane fuel you need to stick with it. 

 

Exactly!......

 

I've been using optimax/vpower/nitro since it first hit the Shell stations up here years ago...my old Fabia (AUB engine) liked it & ran so smoothly on it. & the engine didn't show its age on emissions or power, mind you it was well looked after!

4 hours ago, fabdavrav said:

If will take approx. three full tanks to flush any lower grade out & for the ECU to fully adapt..

 

ie, run car until fuel gauge is in red, fill up fully with super unleaded, run car until fuel gauge is way in the red, fill up fully..etc..

 

Knock sensors & variable camshafts....The 1.4TSI 122/125PS has one variable camshaft...the 140/150PS versions have two variable camshafts...& can really make use of the better petrol..

 

Also cleaning packages in the super stuff is way better than standard fuels, so this stops the ERG systems etc. clogging up as easily...

 

If you run into the red and add 10L and do that 4 times you dilute the old fuel down faster, ending up with 6% old fuel after adding 40L rather than 20% if you do it all in one go. Pain in the rear to do though!

12 hours ago, amwphotos said:

 

If you run into the red and add 10L and do that 4 times you dilute the old fuel down faster, ending up with 6% old fuel after adding 40L rather than 20% if you do it all in one go. Pain in the rear to do though!

 

Which is why I suggest the full tank method...as doing "your" way you also get strange looks from the fuel station attendants...

Try 100 but petrol station isn't on the way. 

 

98 is on the way.

 

Honestly, doesn't feel any difference. 

1 hour ago, fabdavrav said:

 

Which is why I suggest the full tank method...as doing "your" way you also get strange looks from the fuel station attendants...

£15 of fuel doesn't look that odd!

I am one of those people who cannot feel any difference in performance, or spot any difference in fuel economy when using Super within my VRS.

 

My Subaru's were a completely different story. The STI ran like a dog on anything less than 100RON, and the standard UK Turbo produced noticeably more shove when drinking higher RON fuels, especially in the summer.

20 hours ago, fabdavrav said:

If will take approx. three full tanks to flush any lower grade out & for the ECU to fully adapt..

 

 

 

Surely the ECU adapts by constantly monitoring for knocks ie it does not take significant time to adapt? Otherwise if you put a full tank of a lower grade in after using higher grade the car would pink/knock all the time.

 

Granted unless the tank is empty when you fill with a different grade you are running with a mixture, but the ECU must sense that immediately.  

34 minutes ago, juan27 said:

 

Surely the ECU adapts by constantly monitoring for knocks ie it does not take significant time to adapt? Otherwise if you put a full tank of a lower grade in after using higher grade the car would pink/knock all the time.

 

Granted unless the tank is empty when you fill with a different grade you are running with a mixture, but the ECU must sense that immediately.  

 

The whole point of what I stated is that people try one tank & moan that they didn't see any difference.

 

That is BECAUSE they are running a mixture of the old 95ron & the new 99ron thus what they actually have in the tank is not a full pristine 99ron fuel as the tank, pipework, filter, injectors etc. have some of the older 95 ron in them.

 

Yes the ECU adjusts to the immediate conditions, but you will NOT feel the full effects of 99ron UNTIL you flush out the older 95ron TOTALLY from the fuel system! So unless you have all the gear to drain down & clean & purge the older/cheaper 95ron fuel from the systems you have to do what I suggested!

29 minutes ago, fabdavrav said:

 

The whole point of what I stated is that people try one tank & moan that they didn't see any difference.

 

That is BECAUSE they are running a mixture of the old 95ron & the new 99ron thus what they actually have in the tank is not a full pristine 99ron fuel as the tank, pipework, filter, injectors etc. have some of the older 95 ron in them.

 

Yes the ECU adjusts to the immediate conditions, but you will NOT feel the full effects of 99ron UNTIL you flush out the older 95ron TOTALLY from the fuel system! So unless you have all the gear to drain down & clean & purge the older/cheaper 95ron fuel from the systems you have to do what I suggested!

 

Fair point but sorry that's not the same as the ECU taking 3 fills to adapt.

    

The ECU does not take 3 fills to adapt.

I run Tesco Momentum 99 (min) in the UK and occasionally on special days Hiperflo 250 102ron. 

The time for the difference to be felt is the fuel powering the engine.

(100-102 ron Pump fuel in Continental Europe is lovely stuff.)

The trouble is that I don't trust my senses to be able to detect an improvement unless it was pretty marked.

I would notice obvious signs like pinging or hesitant power delivery (certainly experienced it in older cars) but I don't think I would notice a slight improvement in acceleration which is all I could possibly hope for if I up the Octane from 95 to 98.

The only thing I can really trust is my monitoring of fuel consumption and when I did run a few tanks of 98 I did not notice any difference in consumption or anything else for that matter.

I fully appreciate that others may be more attuned to their car than I.

 

I could experiment by putting in the putrid 91 Octane available here in the tank, but I am not that cruel or quite that tight-arsed (it is 12 cents a litre cheaper than 95 Octane).

 

I've run multiple sequential tanks of super unleaded through my VRS and likewise 95RON and I can't say I can perceive any difference in performance.

 

I'm sure the car can produce more power on higher grade fuel but is this likely to be apparent in normal (generally part throttle) driving?

 

I'm sure the power increase will not be more than 10bhp which judging by the VRS 220/230 figures is maybe 0.1secs off your 0-60.  

 

I wouldn't be able to detect that without roadtest timing gear.    

 

Pretty marked when you have Switchable Maps and when you use Dynamic Dynos,  and then when going timed runs, sprints or 1/4 miles, even hill climbs.

13 hours ago, Awayoffski said:

Pretty marked when you have Switchable Maps and when you use Dynamic Dynos,  and then when going timed runs, sprints or 1/4 miles, even hill climbs.

But what gain is due to fuel grade alone? Do you have any comparative figures? Have you run a 1/4 mile on 95 and then on 98/100 with no other changes? I'm genuinely interested in what actual power gains higher grade fuel provides. 

Personally i have never run 95 ron Unleaded in engines with a Recommended 98 / Super fuel requirement. 

Even on some of Scotlands Best driving roads always carrying cans of Super Unleaded 99 + Octane so as not to get caught out North of Inverness on on the West Coast.

As to 97 Ron super Unleaded i have only ever used that where absolutely necessary & no 98 ron is sold in the UK at filling stations anymore but that is what i used and plenty of other did when it was what Royal Dutch Shell & BP had in the UK.

As to Dyno testing with 95 ron and then super unleaded i have never done my vehicles but seen others done, 

i just test the difference with 99 or 102 with cars suitably mapped.

The Octane makes the difference it should, it is not snake oil.

(If you do not want to use Super Unleaded or do and feel or see any more efficient running then you have cars that can run OK on 95ron, 

not all are happy on it but if EU type approved they do run on it.)

http://volkswagen.co.uk/need-help/owners/Fuel

http://en.wikipedia.org/wiki/Octane_rating 

 

The difference between 95 @ 99 at a Tesco Station is 5 pence a litre so under £3 extra on a tank fill, 

and at Sainsburys 95 to 97 is less than that so it is not exactly expensive to do your own MPG testing, 

& if you just want Higher octane for day to day road use then who cares what Detergent Packages or Advertising some Brands put in and put on the media.

Then the  reason for buying Specialist Motorsport Fuels is to get a fuel that can be trusted as consistent and has no Detergent Additives.

Edited 19 April, 20179 yr by Awayoffski

Mazda sell a lot of cars in Australia and part of its popularity is that their cars can take the Australian cheap 91 octane fuel, they even knock the compression ratio of their petrol skyactive range down from the European spec 14:1 to 13:1 for Australia to achieve this.

 

Mazda now do a DI turbo 2.5Litre engine in their updated CX-9 which is fairly unremarkable except for the fact that they have taken advantage of the turbo aspect to design the engine for all markets and you can even put the low ~91 octane fuels in it you get in the US and Australia.

However I remember seeing a reference on the launch that said if you put 98 Octane in then you get an extra 17kW and a nominal increase in torque, I can't remember exactly but something like 10Nm (?).

 

If your car is designed to take advantage of higher octanes then there are definite performance benefits and economy improves by about 1% per octane rating increase.

If the manufacturer of your car recommends 98 octane as a minimum, or if your car is mapped for 98 Octane then I suspect that running a lower octane fuel will incur more noticeable performance/efficiency losses or possible damage.

 

As a sidenote the economy tests conducted here in Australia are mandated to use 95 Octane fuel.

 

I cannot speak for the vRS petrol engines but as I said before when I tried 98 Octane in my 1.4tsi there was certainly no 3% consumption improvement, and believe me I really wanted to see it and was disappointed with the result.

 

I don't touch fuels sold here with ethanol added at 5% because they are only rated at 94 Octane and have a lower calorific value. Most people report poorer consumption returns with this fuel anyway.

 

There is, the closest thing to an impartial proper test that I've seen so far, on YouTube that fifth gear ran. Have a look for it.

 

They concluded, on the car they tested (civic i think?) That there was no power benefit in RON increase.

 

Having said that, they didn't do an economy test and I'm positive i see an overall increase in economy.

Edited 19 April, 20179 yr by Mallettsmallett