Supermarket Fuel

[Rich]

I am confused how people say the standard unleaded and diesel at supermarkets differ from oil company branded stations by so much. Supermarkets have a very quick turn over of fuel so the old stale fuel stories dont hold water and 1 or 2 points of octane or cetane rating difference is not likely as the pumps are all rated with the same specs so the fuel has to reach that spec as a minimum. I have never had an issue with supermarket fuels even on tuned engines as I want to run the lowest octane rating possible before I hit detonation (Pinking)and on some engines I have found an extra 1 or 2 BHP on a low power Kart engine. Then at the other end of the scale on a really high powered 300 BHP Per Litre race bike engine where we used to mix 50/50 116 Ron Octane Low Lead Avgas with full leaded 98 Ron octane 4 star fuel to get a mixed 120 Ron race fuel. Yes the octane went up! But we had access to chemists who could blend these fuels and accurately achive the needed Octane. The petrochemist told us all about fuels and how they work. The chances of fuel from a supermarket and from a branded petrol station being different is almost impossible if you use the standard fuels. The only way they could be different is if the fuel delivered to the branded station is left in the tanks for weeks and some of the volatiles have vented off and lowered it's octane rating. This is very unlikely and almost impossible at a supermarket with the fast turnover of fuel at their stations.

I am sure if someone actually contacted the fuel suppliers you would find most of the fuel stations use fuel as mentioned before from the open market and any contamination from one source could hit any branded station as well. It is only the premium fuels like optimax or V-Power that come from the actual oil company.

The difference in MPG can be effected by atmospheric pressure and humidity as a cold damp night will have an engine produce possibly 2% MORE power than a summers day! I have read the posts and although some feel the supermarket fuels are to blame there can be issues with any petrol station.

If you want a good quality fuel buy the premium branded stuff as the bog standard stuff is just a mix from any local supplier the delivery agent can get a good price from on the day.

 

[Rich]

Just so you can read about race and road fuels..Please read this. It is about 2 stroke race engines but it all still applies to petrol engined cars as well.It also talks about evaporation of volatiles which will lower the octane rating. As I said the pump has to supply fuel to the spec shown as a minimum. New fresh fuels will possibly be higher than shown by 1 or 2 points but in a road vehicle this is not going to make a big difference as fuel injected cars do compensate for this through the ECU and lambda and air flow measurements the sensors make. You need a 5 or 10 point difference to effect how the car runs and as long as the pump you use is the correct fuel specced in the hand book you will not notice a difference.

Fuels - some simple facts.

Two strokes need good fuel to stop detonation lead is by far the best for stopping detonation. To run a similar unleaded fuel you need to drastically reduce the compression.

I would not recommend using an unleaded fuel in a GP bike without a detonation sensor, they just detonate too easily and you would end up either blowing it up or running a couple of sizes rich unless you were very lucky.

Leaded fuels burn a lot slower than unleaded fuels hence the need to ****** the ignition for unleaded.

All fuels are best used fresh, even having a large space in an container that has been opened and then sealed again can let the fuel go slightly stale. Never mix fuel with oil unless you are going to use it straight away and any mixed fuel you have left after a weekends racing should go in the genny.

Two types of octane rating Motor octane (MON) and Research octane (RON), the most significant number for two strokes is the Motor octane as it is measured by actually running the fuel in an engine and increasing the compression until it knocks or detonates

Leaded fuels

Commercial Avgas

very good for detonation MON of 102, RON of 116 but has a wide range in the specs, ie it could be 101 MON in one batch, then 103 MON in the next batch. It is also mass produced like road car fuel and gets mass transported and pumped between tanks most of which are vented to atmosphere through flame proof vents. This means that some of the light stuff which is the good stuff for power can evaporate.

Race avgas

such as 96.7T Elf - very good fuel very consistent hand blended fuel also oxygenated so you are not only putting fuel in but also a small percentage of oxygen. Needs to be up jetted from normal commercial avgas to run the same. All race fuels are manufactured then put straight into sealed containers; there fore they reach you exactly as they were made.

Bluegas

up to 108 MON 124 RON once used to be the dogs danglies when leaded fuels were used in the GPs. You can run very high compression with no chance of detonation. Again an oxygenated leaded fuel with loads of explosive stuff like toluene. Remember the mechanics fueling the bikes in the late 80s with respirators on!! Nasty stuff.

There are other leaded fuels around but unless you get it free its best to stick to fuel that others are using. If you want to use one just have a look at the MON rating and if it is oxygenated.

Unleaded fuels

Normal premium unleaded

I won't even talk about this stuff on a two stroke forum, stick it in the genny.

Super unleaded

Road fuel around 97 RON 84 MON. Great for your RGV or Aprilia road bike, no good for a race tuned engine. Designed for greenness not performance. Like commercial avgas can differ in quality between batches.

Race unleaded

various makes 102 RON up to 90 MON. These are all oxygenated and hand blended fuels. Again you need to up jet from avgas settings along with reducing the compression and retarding the ignition. Without going too deeply into it they are mostly the same now. Only Elf make the GPM2T that is specifically designed for two strokes, Shell made one for a short period but have recently stopped production. Most run to FIM spec which specifies max 102 RON and less than 2.75 oxygen so perform pretty much the same, but as I say look out for the MON rating. I would not recommend swapping too much though as they all have their little differences which can influence the colour of plugs etc. Elf GPM2T is probably the best but at double the price of Carless Hyperflo 250 its probably not that much better.

There are higher octane unleaded fuels available from some of the American fuel people, never tried these but they would be better than the FIM spec stuff. To give an idea you roughly need to go out 1cc on the compressed volume when you go from an avgas type fuel to an FIM unleaded fuel, the highest octane unleaded that can be made would half this.

Race unleaded fuels are the worst for your health apart from Bluegas, some of the stuff they use to boost the octane is carcenegenic! At least the lead only made you stupid!

Information supplied by Stu Jones, he works for BP in their race fuels division that supply the Jaguar F1 team.