Tesco 99 Octane

[flamespitter]

Guys,

Used Tesco 99 for the first time this week.
Unless it was my imagination (very possible/likely)
the car felt extremely smooth particularly at the bottom end.

The sites which stock this high octane fuel are found on this link;
www.greenergy.com/products/99_octane_locations.html

What is the general feedback on this fuel?

[supersport]

Made its way oop north now, we have had it York for ages, they replaced all the old Tesco Super Unleaded with the new 99 stuff. Haven't used it though.

[ripton]

I've been using it for a couple of months and my 944 turbo loves it but there has been little noticable improvement in my wifes 2.0 FSI A4.

Combination of Tesco's Finest RON and the super cold weather and the turbo was a different beast, straining on the leash as it were. Shame about the slime on the roads preventing serious exploitation of such a combustible combination

Chris

[Raven Flyer]

I use it in my 996 NA and its definitely better than BP/Texaco/Esso super for normal recreational driving. No Shell garages near me so I can't compare with Optimax, but suspect the two are similar. The last time I found Optimax it was 10p or so more than Tesco 99.

One word of warning, consumption is 7-10% worse with the Tesco stuff. I noticed that the long term average had dropped from 22mpg to 20mpg, over a few thousand miles, so researched the fuel. It contains 5% bio-ethanol which is what ups the RON rating, but it delivers less energy per litre. because the ECU will advance the timing to suit the RON, you get more power, but end up using up to 10% more fuel to realise the potential.

As the stuff is cheap, this isn't a problem. I wouldn't want to pay a premium for it though.

[supermono]

I'm fairly confident that my tt goes a bit better all round with optimax compared with the Tesco.

Presumably it's not just the octane that matters, though one's engine management system can be a bit more enthusiastic. It's also the amount of energy contained in each pot full? It's all very well being able to advance ignition so max pressure occurs at the right time, but if that max pressure is less it may not make as much torque.

Be interested in knowing from someone clever.

SM

[t urbo]

Ive run my car on Sunoco GT plus which is 109 Ron and with the ecu in stock mode i couldnt feel any difference between that and your regular unleaded.

I think power increases are part of the imagination.

The tt's ecu is programmed to run peak power on 98 ron, any higher will make little to no difference in bhp let alone being able to feel the difference.

Even with my car switched to the race program and running 109 Ron it only produces an extra 15bhp ( over the pump program which produces around 550-600 hp) which again is really hard to feel.

That said i wouldnt hurt to fill up with tescos fuel since its the cheapest around.

Like Ripton said, Cold air is the key to better response and the power difference you may 'think' you feel.




>> Edited by t urbo on Thursday 20th April 19:01

[cyberface]

It's the same strength as Stella IIRC, so it should be OK.

[willibetz]

supermono said:

I'm fairly confident that my tt goes a bit better all round with optimax compared with the Tesco. Presumably it's not just the octane that matters, though one's engine management system can be a bit more enthusiastic. It's also the amount of energy contained in each pot full? It's all very well being able to advance ignition so max pressure occurs at the right time, but if that max pressure is less it may not make as much torque. Be interested in knowing from someone clever. SM

Very simplistically, as I'm a bit pushed for time, the Tesco fuel contains an oxygenate. Therefore you can burn more of it for a given mass of induced air, which means that you can derive more power. In this instance, it's the mass of air that you can pump that is the constraining factor, not octane quality or the ignition map.

Hope that helps, until someone clever becomes available

[cyberface]

It's 5% alcohol (ethanol). Ethanol contains oxygen so can be seen as already partially-burnt fuel... burning ethanol produces less energy than burning the same molar quantity of ethane (the relevant hydrocarbon).

However ethanol has a higher knock resistance (octane number) and thus can be raised to higher compression ratios in engines without detonation. Higher compression ratios allow higher power outputs.

On normally aspirated engines, I'd reckon the primary benefit to Tesco 99 is environmental i.e. the ethanol is 'bioethanol' and comes from renewable sources. The fractionally lower calorific value of the (only) 5% ethanol mix is probably offset by the ability for fractionally more ignition advance.

For turbo engines, the increased knock resistance will allow the ECU to maintain higher boost levels without detonation, thus producing greater power outputs in less than ideal conditions (i.e. high ambient air temps, etc.).

Premium branded fuels such as Optimax also contain detergent-type additives that may be helpful to an engine regardless of power production potential, however.

[cyrus1971]

I use it all the time in my 996TT and it's good for a few extra BHP over Optimax, say 5 at most and the smoothness is definitely there as you say.

[Fatboy]

cyberface said:

It's the same strength as Stella IIRC, so it should be OK.

Will it also cause your car to be generally more aggressive?

[semprini27]

I use it in my 1988 3.2 Carrera and it definately prefers it. Starts cleaner when it's been abandoned for a week or two and runs much smoother and keener when up to temp.

Optimax is only slightly better than normal juice in my motor so Tesco is the favoured brew.

[anonymous-user]

on the 'aggro' map on my old s4 tesco's and opti ran fine, bp and texaco pretty bad (ecu occasionally shutting boost to prevent knocking) and esso like cr@p (needed bottles of octane booster and optimax shandy to work )