Hello,

I am on my second tank on fuel at the moment, both times I fueled up I used normal petrol.

I am wondering with the Fuel Stratified Injection, should I use the high octane fuel to keep the injector clean?

I did a quick search and on an Audi forum, they say using normal fuel will increase timing? and increase the chance of a knock on engines - this seems quite silly to me, is it true??

Some go as far to say the extra cost at the pump will compensate itself on increased MPG??

I am highly sceptical of high octane fuel, so could someone change my mind?

Thanks

Hello,

I am on my second tank on fuel at the moment, both times I fueled up I used normal petrol.

I am wondering with the Fuel Stratified Injection, should I use the high octane fuel to keep the injector clean?

I did a quick search and on an Audi forum, they say using normal fuel will increase timing? and increase the chance of a knock on engines - this seems quite silly to me, is it true??

Some go as far to say the extra cost at the pump will compensate itself on increased MPG??

I am highly sceptical of high octane fuel, so could someone change my mind?

Thanks

I wouldn't change your mind. If you do not need the high octane and the standard fuel is within specification, you get no benefit from high octane. Some "enthusiasts" will disagree with this.

You should use high octane fuel. The ECU will advance the timing to suit and run better and smoother with more power.

You should use high octane fuel. The ECU will advance the timing to suit and run better and smoother with more power.

That is what Ive always found to be the case but others do disagree and insist Im imagining it!

You should use high octane fuel. The ECU will advance the timing to suit and run better and smoother with more power.

REALLY?

I suspect the tiing advance is controlled to take advantage of the fuel Octane specified. No more. If lesser fuel is used and knocking is detected (long before humans recognize it) the timing is retarded to avoid damaging knocking.

I would really like to be convinced otherwise with some sound technical references to back up any statements. It has been a niggling un-resolved question for many years. Used to be you built the motor, ran it and if did not knock, advanced the timing til it did, and then backed off a bit. But, that was Holley double Pumper days and breaker controlled ignitions, no digital controls at all.

I would really like to be convinced otherwise with some sound technical references to back up any statements. It has been a niggling un-resolved question for many years. Used to be you built the motor, ran it and if did not knock, advanced the timing til it did, and then backed off a bit. But, that was Holley double Pumper days and breaker controlled ignitions, no digital controls at all.

Well that's exactly what the ECU does for you

Well that's exactly what the ECU does for you

Sorry, Shark, but the statement is not an explanation or even a convincing argument. Note that the ol' fashioned way was "static" - meaning that the advance was set and did not change on a running engine. I still believe the staus today is the same, except the ECU retards form the set pont for safety - not advancing beyond the static maximum set point.

....and , please, I don't want this to turn into a he said, she said type of exchange.

I don't know how to explain it in any better terms to be honest, but the ECU has the "map" stored in the flash inside the ECU. The processor doesn't just run to the map, it also has "learned values" which it can use to interpret the map in its own way and can adapt to fuel quality and intake temperature amongst many other things. It even measures altitude and air pressure and compensates for them.

Bosch ECUs have done this for yonks and so do many of the other manufacturers' ECUs too.

I don't know how to explain it in any better terms to be honest, but the ECU has the "map" stored in the flash inside the ECU. The processor doesn't just run to the map, it also has "learned values" which it can use to interpret the map in its own way and can adapt to fuel quality and intake temperature amongst many other things. It even measures altitude and air pressure and compensates for them.

Bosch ECUs have done this for yonks and so do many of the other manufacturers' ECUs too.

I don't really want to take this too far, as I am a convinced Diesel nerd at the moment.

One interesting thing would be to have a dyno run with for example 95 and 100 octane on the same car. Has this been done?

My Yeti manual states that no advantage will be gained from running higher octane fuel and that the car should be run on regular 95 RON fuel. As I read it, the car will compensate for lower 91 octane fuel as a temporary measure but this is to be avoided for long term use.

Personally I use Texaco or BP regular 95 unleaded. I have considered using BP ultimate but from what I have read it takes a few fills to realise any benefit in fuel economy and performance. Not so long ago What Car? (I know it is generally awful) carried out a fuel test and the best all rounder for economy was Sainsburys regular unleaded. I don't use it myself because I like to think that the detergent mxture in the branded fuels will keep my engine running smoother in the long run. There has been a lot of comment on another VW forum about supermarket fuel harming the earlier FSI engines although these are no longer in production. If anyone knows of a published test of the detergent / lubricant qualities of branded v supermarked fuels I would love to read it.

Don't think a 2 point octane increase would be that noticeable in reality. Best example I've read of a increase being useful was putting 150 octane (normally 100) in Spitfires so they could catch flying bombs. Burnt the Merlin 66 twin charger engines out in short order though :(

TP

One interesting thing would be to have a dyno run with for example 95 and 100 octane on the same car. Has this been done?

Yes: http://www.youtube.com/watch?v=Ospimy_4j9k

In short, it shows that more highly tuned cars adapt themselves to make use of higher octane fuel, whereas 'normal' cars don't.

Edited 17 May, 201016 yr by AdamR

Yes:

In short, it shows that more highly tuned cars adapt themselves to make use of higher octane fuel, whereas 'normal' cars don't.

Thanks for the different views. I am actually wondering about the detergent content.

Am I right in saying that FSI is more efficient as the petrol mist that comes out from the injector nozzle is finer and therefore it burns better.

If this is the case, I am wondering if the more expensive fuel (ie the superunleaded things) would be better in the long run for the injectors?

Thanks for the different views. I am actually wondering about the detergent content.

Am I right in saying that FSI is more efficient as the petrol mist that comes out from the injector nozzle is finer and therefore it burns better.

If this is the case, I am wondering if the more expensive fuel (ie the superunleaded things) would be better in the long run for the injectors?

Ok this is my understanding of things based on my time at VW and what I have read since leaving five years ago. FSI engines suffered a number of failures and poor quality fuel was blamed in all cases. Many technicians were adamant that this was supermarket fuel without the same additives as the branded fuels. VW then changed the design and effectively abandoned the original Fuel Stratified Injection design but kept the FSI name. I have heard this from a number of sources and so if anyone would like to back this up or dispute it ...........

95 RON fuel from Shell has the same detergents in it as 99 RON V-power. You don't use high octane fuel to clean the engine, you use it if the engine is tuned for it.

The 1.2 TSI is set up for 95 RON fuel. Just use that, you won't get any benefit from higher octane, you would be throwing money away. If you use it, the engine will compensate by adjusting timing, but you won't get extra power and your economy could go down until you get back to the proper fuel.

@ My_Yeti - the 1.2 doesn't use the FSI system anyway AIUI.

Edited 18 May, 201016 yr by Mike Wrightson

95 RON fuel from Shell has the same detergents in it as 99 RON V-power. You don't use high octane fuel to clean the engine, you use it if the engine is tuned for it.

The 1.2 TSI is set up for 95 RON fuel. Just use that, you won't get any benefit from higher octane, you would be throwing money away. If you use it, the engine will compensate by adjusting timing, but you won't get extra power and your economy could go down until you get back to the proper fuel.

@ My_Yeti - the 1.2 doesn't use the FSI system anyway AIUI.

Thanks for explaining the detergent part, in whcih case I will stick to normal 95 RON.

I am pretty much 100% sure that it is a FSI (well TSI) engine, even though it doesn't say TFSI, as I think TFSI is reserved for the twin charged FSI engines.

It uses direct injection, but not FSI (as far as I have read). The two are not necessarily the same thing.

I am sure that Yeti does not use FSI as per the original technology launched at the beginning of the decade. They are TSI engines.

Good video about the TSI:

Thanks, in that case I will stick to the normal 95 RON fuel then