Shell vs Super market petrol !!

[Scruff]

Why would the amount it compresses make a difference?

Cool air is denser - i.e. has more oxygen molecules. All modern cars have sensors to detect the air pressure or temperature going into the engine and can squirt in more fuel to keep the ratio the same. More fuel + more air = more power. Whether that produces better MPG too I'm not sure.

The real question is why does a 2 litre car use more fuel trundling along slowly than a 1 litre car? If they could just solve that, then we could all have twin-turbo 5 litre V8s and still get 60mpg on a trip to the shops.

Larger reciprocating masses...

[Old Hack]

The idea of more power meaning more MPG is that you use less time on the throttle getting up to cruising speed, and it’s at cruising speed you see more fuel savings. I have had our cars remapped. My car used to do, maximum, 32mpg on a run, but if you’re about town, that shrunk to 21. I have had this chipped,with 24% more power, and 33% more torque, and now the figures are 36 and 22. The around town one I didn’t expect to change much, as you are still off and on the gas, and that’s where most fuel is used.

Having said that, with the torque the car now has, I have trouble not travelling everywhere too quickly, so I am hoping that feeling goes away fairly quickly.

I also did the Motorhome, and fuel consumption was transformed from 22mpg to 32.

[Paddy]

The reason why engines have a turbo and some even have air compressors. Intercoolers cool the air. SAAB used to have a water spay device to boost power. Some people have fitted their own waters spay devices with an evaporator, these helps the lack of power in hot climates.
Large engines are less efficient at low speed, hence an 850cc engine is better for around town

BTW, you can make you own Shell secret additive to petrol and diesel by adding a very small drop of acetone.

[BolshieBastard]

Hi,

I used to fill petrol from my local Morrison’s, recently moved to Shell petrol. Looks like Shell gives me 50-80 miles extract per full tank!. Is this due to 'superior' Shell Petrol or change in weather? My journey route is not changed in last 3-4 months.

Utter rubbish! Unless you are using the 'neck to neck' technique, any such assertion is baseless.

I've put shell premium diesel, bp ultimate diesel etc in mine and the ony difference was in my wallet by some 10p a litre!

5th Gear recently did a full on comparison and found there was no noticible difference in performance, bhp or mpg between using the supermark fuels compared to branded. But, if you want to believe the marketing hype........

[darmstadt]

The real question is why does a 2 litre car use more fuel trundling along slowly than a 1 litre car? If they could just solve that, then we could all have twin-turbo 5 litre V8s and still get 60mpg on a trip to the shops.

Does it? I recently saw a report on TV which showed a Prius and an M3 doing 10 laps of a track at the same time with the Prius in front. At the end of the test the M3 had used less fuel! Basically it comes down to how you drive a lot of the time.

[Old Hack]

Does it? I recently saw a report on TV which showed a Prius and an M3 doing 10 laps of a track at the same time with the Prius in front. At the end of the test the M3 had used less fuel! Basically it comes down to how you drive a lot of the time.

And also the fact the Prius with it's 100bhp motor pulling more weight than the 400bhp M3, is laboured all of the time, at full tilt.

It was disingenuous at best; if you buy a prius, you're not going to be winding through the gears setting lap times; it's an auto, and meant for cruising, to save fuel. Now, put him in a 335d (smaller engine) and get him to race that around the track, and it would be a far different story.

Really annoys me when people do that. The prius was at maximum revs all the time, and all the M3 had to do was stay behind it, pootling about in top gear. Grrrr.

If you have more power, and the same weight, you will mostly use less petrol, if you drive the same. the sole caveat being if you're on the door handles all the time. More octane, is more power, so logically, it of course should be true.

A swedish study once showed the best way to drive, in order to be fuel efficient, was to accelerate to your speed as fast as you can, then stay at that speed as long as you can, with minimal changes to acceleration, and deceleration. If you try and do this, you become a better driver, for you look out for traffic lights more, and notice queues so you end up planning a journey better, i.e. you look ahead and slow slightly, trying to ensure you don't have to come to a proper stop.

[original PM]

And also the fact the Prius with it's 100bhp motor pulling more weight than the 400bhp M3, is laboured all of the time, at full tilt.

It was disingenuous at best; if you buy a prius, you're not going to be winding through the gears setting lap times; it's an auto, and meant for cruising, to save fuel. Now, put him in a 335d (smaller engine) and get him to race that around the track, and it would be a far different story.

Really annoys me when people do that. The prius was at maximum revs all the time, and all the M3 had to do was stay behind it, pootling about in top gear. Grrrr.

If you have more power, and the same weight, you will mostly use less petrol, if you drive the same. the sole caveat being if you're on the door handles all the time. More octane, is more power, so logically, it of course should be true.

A swedish study once showed the best way to drive, in order to be fuel efficient, was to accelerate to your speed as fast as you can, then stay at that speed as long as you can, with minimal changes to acceleration, and deceleration. If you try and do this, you become a better driver, for you look out for traffic lights more, and notice queues so you end up planning a journey better, i.e. you look ahead and slow slightly, trying to ensure you don't have to come to a proper stop.

Indeed it is all about how you drive.

I had a ford with an eco boost engine as hire car recently - it returned less mpg than my standard 2.0 diesel mondeo when cruising at (ahem) 90 - (which if you want to get to Scotland up the M6 in any decent time is about right) so yes very efficent at 56 mph but then aren't all cars?

[Old Hack]

Indeed it is all about how you drive.

I had a ford with an eco boost engine as hire car recently - it returned less mpg than my standard 2.0 diesel mondeo when cruising at (ahem) 90 - (which if you want to get to Scotland up the M6 in any decent time is about right) so yes very efficent at 56 mph but then aren't all cars?

Too true. When I first left uni, wifey and I had a little diesel fiat. I could only get 57 driving like a church mouse, whereas she could hit 70mpg. What annoyed me the most about this, is I was trying really hard to get the lowest mpg, and she didn't even know we were playing a game...

I have a big 4x4 but once up to speed, it provides decent ish MPG. However, getting to and from that cruising altitude kills it.

[tranceporter]

Too true. When I first left uni, wifey and I had a little diesel fiat. I could only get 57 driving like a church mouse, whereas she could hit 70mpg. What annoyed me the most about this, is I was trying really hard to get the lowest mpg, and she didn't even know we were playing a game...

I have a big 4x4 but once up to speed, it provides decent ish MPG. However, getting to and from that cruising altitude kills it.

If you mostly drive motorway miles, it is actually more efficient to get cars with a bigger engine (V6 or V8). My 6lt VXR8 does 2.2k rpm in 6th gear when doing 80mph. It consumes the same fuel as my 2.3T Mazda 6 MPS, which is doing 3.5k RPM in 6th gear at 80 mph, which means the turbo is dishing out boost, which is turn means increased fuel consumption. If it's urban driving, I would drive the MPS, but end up using the VXR8 to race the chavs. Oh the fun!

[doodab]

I floor it in 2nd all the time. It's fun.