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[106rallye]

With unleaded I get about 45 / 50 miles less per tank when using normal unleaded than using super unleaded, the difference in cost outweighs the lower miles so I reckon there is no real difference in cost.
quote]


Might seem a silly question to some but why would you get more mpg with higher octane fuel?  I thought it'd be the other way round if anything. Isn't a set amount of fuel squirted at a given time...how does the engine know it's higher octane?

High octane fuel burns better so less of it is needed.

[jemis]

With higher octane fuel it burns better in the chamber giving a stronger explosion and therefore needs less fuel to give the same performance, the lambda sensor in the exhaust will tell it what fuel air mixture is going in through the gas coming out and adjust the amount of fuel to suit.
When driving with a heavy foot the consumption will not change or may even drop so it only really works when cruising on motorways etc.

[jemis]

To go back to original question if your car was remapped while running on v power I would stick to super plus fuel as the fuel map set points will have been changed in the ecu.

[Neil_MV6]

Cheers for the clear explanation.  I do loads of miles so I'll give it a try.

You learn something new every day.  

[Entwood]

Neil.... I notice a substantial difference when towing long distances at steady speeds .. ie motorway stuff .. on "cheap" unleaded (sainsburys's ?) I'll get around 16-18 mpg .. on Shell V  its 20-24 mpg. Once off motorway where you are always changing the power the difference is negligible but the car seems to perform better.

HTH

[Neil_MV6]

Well I hope I see similar benefits.  At a steady 70mph I can achieve 37-38mpg, around town it drops to 23ish.

I'll report back in a week or so and let everyone know.

I can't believe I didn't know this!  

[Kevin Wood]

I notice a substantial difference when towing long distances at steady speeds ..

This is precisely where you will notice a difference.  Long periods of heavy load are the most likely to generate knock because valves, pistons, plugs, etc. are at their hottest. Running poor fuel makes it more likely that the fuel will pre-ignite under such conditions. This will be detected by the knock sensors and the ignition retarded to a less efficient, but safer, setting, hence fuel economy is better with a fuel that won't knock in the first place.  

Pootling around town you never get sustained heavy loads for long enough and are on very low engine loads for most of the time, where knock is very unlikely with any fuel.

Due to the additives in super unleaded (some brands contain a lot of ethanol) there is less energy per litre in some super unleaded than regular, which may explain the worse fuel consumption.

Kevin

[SP_3.2]

I drive 60 miles a day most M ways and as you say i find that is when i have the most from the V-power. the cost is £1.08 and if i put in £15 i get about 110 miles which i think is good on it  Not sure how that works out in MPG ?.

I have since the weekend gone back to V-power and althouth it cost more the car seems a lot better on it, with better pick up and MPG on the long runs.    

[Neil_MV6]

SP, you mentioned you've had a re-map.

What exactly does this do and what are the benefits?

[SP_3.2]

Hi well it was done about 18 months ago and it took the BHP from 231 to 245 on a rolling road and when remaped to 97+ ron has helped the MPG as you know the 3.2 v6 love to drink. This is best to the long runs but every bit helps. Cost me £250 and had a print out of the BHP befor and after. It was do by a company called chipped uk.

Hope that is of help.

P.s Your car looks v. good.        

[Pitchfork]

Neil.... I notice a substantial difference when towing long distances at steady speeds .. ie motorway stuff .. on "cheap" unleaded (sainsburys's ?) I'll get around 16-18 mpg .. on Shell V  its 20-24 mpg. Once off motorway where you are always changing the power the difference is negligible but the car seems to perform better.

HTH

Does the same apply for Diesel from the likes of Sainsbury's??
IW

[Neil_MV6]

Cheers mate, I'll look into that.  I'm going to be doing some silly miles and after reading this thread in particular, will be using the higher octane fuel (if the economy does improve).

My car's in great condition externally and the engine si smothh as silk, even with 150k, however it's starting to show it's mileage in some areas such as suspension bushes, shocks etc  Luckily my new job pays a decent car allowance which will pay for all the little things that need doing.

What colour's yours?

[SP_3.2]

Mine is Blue with the tan leather and has 130 on the clock. If i can be of any more help just PM me

[TheBoy]

My mate reckons you can get 20lt of veg oil from tescos for £10

OK so how can I run my TD on Tesco's finest?

seem to recall the beemer injection pump isn't a fan....

[TheBoy]

Neil.... I notice a substantial difference when towing long distances at steady speeds .. ie motorway stuff .. on "cheap" unleaded (sainsburys's ?) I'll get around 16-18 mpg .. on Shell V  its 20-24 mpg. Once off motorway where you are always changing the power the difference is negligible but the car seems to perform better.

HTH

Does the same apply for Diesel from the likes of Sainsbury's??
IW

yes.  see how much less diesel smoke (ultimately unburnt diesel) you get after a couple of tanks of bp diesel...