October 2008 Fuel Test Report
By John Thorne
Do You Get What You Pay For?
Comparing the fuel economy of Tesco 99 Octane and Tesco 95 Octane petrol.
Introduction
If we are honest with ourselves we at Thorney Motorsport are quickly becoming fuel nerds. We’ve been testing fuels for so long now that every trip to a forecourt has become a point for data collection let alone re-filling a fuel tank. This is the third test of fuels we have undertaken in the last three years testing various UK fuels over 100,000 miles and whilst the process of testing is never really completed we feel confident that the results are a benchmark against which other tests can be measured.
Thorney Motorsport are one of the UK’s largest car tuning companies. Specialising in BMW and Vauxhall cars we are unique in being the only tuning firm which also has full authorised repairer status from a manufacturer. We specialise in the performance enhancement of road cars and commercial vehicles as well as a large racing team which races Vauxhalls and BMW’s. Our interest in performance fuels stems from the fact that as performance enhancers we are always looking for ways to improve the power of a vehicle, this testing process has included extensive duel testing over the past three years.
In our first fuel test conducted in 2006 we compared Tesco 99, Shell Optimax, BP Ultimate and Total 95 standard fuel to determine the power gains achieved by each fuel. The full report can be found here. Our second test a year later was an update of the first test and compared Tesco 99 Octane, Shell V-Power, BP Ultimate and BP Ultimate 102; this report can be found here. In both these tests we concluded that Tesco 99 Octane fuel gave the best results in terms of outright power and consistency compared to the other fuels. In both these reports we used a normally aspirated engine car (a BMW M3) as it represented a high quality engine design with sophisticated engine management control.
Since our last test results were published in 2007 the price of oil has continued to rise and fuel has become a larger proportion of overall motoring costs. The purpose of this new test was therefore to measure higher octane performance fuel against a standard 95 octane fuel to see if performance fuels help or hinder your MPG.
How We Tested
We created two test conditions for this fuel test. Firstly we tested two cars in their standard condition (the vehicles computers were running standard software as supplied by the manufacturer). Once this round of testing was complete we modified both cars and tested again, this time running on enhanced ECU maps (the ECU was upgraded to allow the cars to run with more power). We measured power output and MPG in both cars in both test conditions on both types of fuel to see what effect running on 95 octane and Tesco 99 Octane had. The cars remained mechanically unchanged for all parts of the test. We used Tesco fuel because Tesco’s 99 Octane petrol has proven to be the best performance fuel available in the market. We used Tesco 95 octane fuel to ensure there was no suggestion of bias.
The testing process was simple. Each car was driven until the fuel gauge showed empty, re-filled with the selected grade of fuel and repeated twice more. The car was strapped down to a Dyno Dynamics Chassis dyno, tested, then the process repeated at each third tank of fuel used. These tests were then repeated when the cars had been modified. Hardly rocket science!
We have used our dyno for the previous fuel tests and saw no reason not to use it again here. A chassis dyno (also called a rolling road) is a sophisticated piece of equipment used to measure (amongst other things) a vehicle’s power output. The car is strapped down onto the dyno and driven as normal whilst held in a static position. This allows us to measure every aspect of the engine from power to exhaust gases. Large fans are used to keep the engine cool during this process. The accuracy of our dyno cell has been proven beyond doubt - several manufacturers and race teams make use of it for testing purposes and EVO magazine use it to test the power claims of manufacturers.
The Cars
For this test we used two Vauxhall Astra VXR’s and we did so for three reasons. Firstly, because this is a model we have a great deal of experience with, having extensively upgrading the road cars in our tuning centres. Secondly we run our own race Astra VXR in the Dunlop SportMaxx Championship and thirdly, it represents a perfect example of the types of cars manufacturers are now electing to build. Current emissions regulations mean manufacturers are moving to forced induction (turbo chargers and super chargers) in order to create engines that offer both reasonable power and lower emissions. The 2.0 litre Z20LEH engine in the Astra VXR is General Motors’ latest development on the Vauxhall range and it benefits from high quality construction together with advanced Bosche engine management. It’s a good engine with a good computer controlling it.
The cars we used are actually owned by members of staff at Thorney Motorsport:
| Car Number One |
Car Number Two |
| Vauxhall Astra VXR Engine: 2.0 Litre Z20LEH (Turbocharged) ECU: Standard, then Modified Exhaust: Milltek Sport Full System Mileage as Tested: 33,626 Year of Registration: 2006 Type of Driving: Urban, with weekend motorway. |
Car Number Two Vauxhall Astra VXR Engine: 2.0 Litre Z20LEH (Turbocharged) ECU: Standard, then Modified Exhaust: Milltek Sport Full System Mileage as Tested: 55,472 Year of Registration: 2006 Type of Driving: Daily Commuter, 90 Miles per Day |
The Results
Test 1: Cars in standard condition
In the first test we ran the cars in the standard condition (no modifications or ECU mapping):
These charts show the two cars power and torque figures as tested on the dyno. The upper pair of lines charts the cars power as measured at the flywheel against the left hand scale (S-HP). The lower pair of lines shows the cars torque as measured at the flywheel against the right hand scale (llb). The red lines show the cars power and torque when the car is running on Tesco 95 octane fuel and the blue lines show the car running on Tesco 99 Octane fuel.
The differences between the two fuels are clearly evident. Throughout the rev range the two cars are broadly similar.
But, as the revs increase the better power generation of the higher octane fuel becomes clearly visible. On the road this power difference is manifested by the 95 octane car feeling ‘strangled’ at higher rpm whereas the 99 Octane car continues to pull cleanly through the rev range.
In pure power terms the 99 Octane fuel provided over 15bhp more power than when the car was run on 95 octane fuel – nearly 9% - a noticeable gain in performance. However, a performance gain from running a performance fuel is a logical outcome. The real question this testing was hoping to answer was this: are the performance gains of the higher octane performance fuel really worth the extra cost?
Fuel economy is notoriously difficult to measure. The variety of influences that come into play when measuring fuel usage are impossible to replicate in a laboratory. Issues such as weather conditions, wind, road type, road surface, driver style, traffic all effect the outcome of fuel usage to such an extent that any effort to standardise MPG is typically impossible. There are just too many variables.
Rather than try and calculate fuel usage using one of the more traditional laboratory methods, we thought we’d just be very simple about it and measure fuel use as anyone would. Measure the fuel going into the tank and measure how many miles you got until the tank was empty – simple! As a back up the car owners also noted the fuel economy measured by the cars on-board computer.
The results are pretty startling:
Standard car running on Tesco 95 Octane fuel – Average 22MPG
Standard car running on Tesco 99 Octane fuel – Average 25MPG
This equates to over 10% improvement in fuel economy. During the test period the average cost difference between the two fuels was 4.5% so the effect of 9% improvement in power and 10% improvement in fuel economy means that the additional cost of running Tesco 99 Octane fuel pays for itself from the first tank.
The Results
Test 2: Cars in Modified Condition
For the second test we modified both cars with enhanced ECU maps by upgrading the engines computer software to enhance the power of the car before repeating the tests. The same methodology was used as in test one (three full tanks of fuel, dyno tested and repeated and the fuel measured into the tank and the miles recorded exactly).
The results are even more startling:
The difference in power for the cars is dramatic. Whilst running on 95 octane fuel the car still gives more power than standard (peak of 255bhp), but when run on the 99 Octane fuel power is increased a further 30bhp. That’s over 10% difference just between the two fuels! This power difference manifests itself clearly on the road. The car feels flat and lethargic when running on the 95 octane fuel whereas on Tesco 99 Octane it feels transformed with a sharper throttle response and improved acceleration.
What was really interesting was the effect that remapping the ECU had on fuel economy:
Modified car running on Tesco 95 octane fuel – Average 25MPG
Modified car running on Tesco 99 Octane fuel – Average 32MPG
This resulted in a huge 28% increase in fuel economy just from running different quality fuel in a modified ECU car. The comparison between a standard car running on 95 octane fuel and a modified car running on 99 Octane fuel is even more dramatic – a 48% increase in fuel economy!
| Tesco 95 Octane |
Tesco 99 Octane |
|
| Standard Car |
22 MPG |
25 MPG |
| 235 BHP |
252 BHP |
|
| Modified Car |
25 MPG |
32 MPG |
| 255 BHP |
283 BHP |
Conclusion
The conclusions are pretty obvious as the test results speak for themselves. By running an Astra VXR on Tesco 99 Octane you can improve power by 10% and improve fuel economy by another 10%. If you then upgrade the cars ECU you can achieve almost 50% improvement in fuel economy over a standard car.
The question all of this poses is the following. Why does the better fuel give such dramatic gains in terms of fuel economy and power? And why does changing the software have a similar, additional effect?
There are a variety of reasons as to why the fuel quality has such an effect.
Firstly an engine is simply a controlled explosion where air is mixed with fuel and ignited via a spark and the more oxygen the air has in it, the larger the explosion and more power is created. By using a fuel with a higher octane level the fuel is able to burn at a more optimum temperature and for longer (known as flame rate), therefore generating the power required by the driver. This means that less fuel is required to achieve higher levels of power. Lower octane fuel requires the car to work harder, using more fuel to achieve the power demanded by the driver therefore increasing overall fuel consumption. There is such a thing as quality in fuels.
Secondly this effect is magnified by the fact that these particular vehicles have forced induction turbo chargers. More and more modern vehicles are being developed with turbo chargers which create extra heat in the engine. Hotter air contains less oxygen which means the engine must work harder to generate power, but the higher ethanol content in Tesco 99 Octane means the fuel is more resistant to this effect, so it can still generate power without requiring more of it.
The concept of using upgraded software in a car’s computer is not a new one; indeed there is an entire industry offering this service to car and commercial vehicle owners. However this is the first time anyone has actually measured the effect of this on fuel economy. When developing a car’s software, manufacturers have a variety of rules and regulations to adhere to none of which apply once the vehicle has left the factory. They also need to build in an element of power improvement throughout the model life of the vehicle and ECU upgrades are part of that process. What Thorney Motorsport does is upgrade the cars ECU software with a version that allows the car to run more power. Cost wise this can be as little as a few hundred pounds.
What is clear from this testing is that the cost of upgrading the cars computer software is immediately repaid via better fuel economy and, combined with the extra power, it really becomes a very desirable process to undertake. If this is also combined with running the car on Tesco 99 Octane, the cost savings are clearly significant.
There is such a thing as a quality fuel. In these tests we have simply compared Tesco’s standard 95 octane fuel with its premium version 99 Octane fuel and it is clear that on a like for like basis the cost savings from using the higher octane fuel easily surpass the initial higher cost at the pump. Combining this with upgrading your car’s ECU software will increase this saving further and in the high petrol price environment today you’d be mad not to do it!
John Thorne
Thorney Motorsport
September 2008
