MrEngineerdat

I wonder if this is something they dont want you to know, or even if anyone can answer this one? (i like to drive briskly but still manage good mpg's)

example.....

You have to get from roundabout 1 to roundabout 2, they are approx 1/4mile apart, the road is fairly straight and has no gradient.

Using the same car under the same conditions - What would be more economic; situation A, or situation B?

A:- You drive quite casually off roundabout 1 and steadily increase speed, using gears all the way to the other end at roundabout 2.

or

B:- You fly off roundabout 1, with wide open throttle, accelerate to a sufficient speed to get you to the end, and coast the rest of the way, with idle revs to roundabout 2.

.................................................. ..............

Yes, situation B uses lots of fuel and might cause more wear on the car, but it saves incredibly on fuel in the second half... while situation A would take longer, and more power strokes will have taken place... So is it just even?

What uses more fuel? thats the question!

Eigdoog

B, as you have opened it wide open and fuel will flow in a lot then it still needs fuel to tick over so to speak.

Plus having a blast from a roundabout can be fun i guess

Thats my 2p!

alistairolsen

Neither, use about 80% of peak torque at sensible revs to accelerate through the gears until you have just enough speed to coast and arrive at the second roundabout at a suitable entry speed without needing to brake.

Sadly this is impossible as you have to share the road with spods at both ends and your speeds will be compatible for about 5 feet....

markk

iTrader: (2)

The problem with B is an engine actually runs very rich at idle speed, what you would want to do is stay in gear and coast/decelerate this way to the next section, that way the ECU will allow fuel cut off on overrun thus saving fuel, do a bit of research on 'pulse and glide'.

MrEngineerdat

Pulse and glide... never heard of it before but read up on it and realised i do that sometimes - more useful on shorter roads, not so much motorway.

Why would it run rich at idle speed???
Isnt it the idea to maintain correct air/fuel ratio? (except on a cold start or choke)

markk

iTrader: (2)

But at cruise you will actually run quite lean, if you have any of the latest DI petrol engines then you may even see 22:1 on cruise, never mind 14.7:1 at stoich.

Energy extraction from petrol has historically been very poor, approx. 35% of the energy from the fuel goes to propelling the vehicle, the rest has always been wasted.

Bailes1992

I have to drive for economy to afford to get back and fore work. (Approx ~80m one way).
The most economical way to drive my car is to accelerate briskly, when upto speed cruise with the engine revs around peak torque and try engine brake as much as possible.
Got to be doing something right! On a run back and fore Nottingham in the summer I managed 74mpg

botters

iTrader: (2)

carry enough speed out of roundabout 1 to propel you to roundabout 2 with the engine switched off and gearbox in neutral lol

James B

....and steering lock on as thats what you deserve. lol

CrOwSoN15

Ignition on?

Maxwell

Fuck i laughed LOL

Eigdoog

Thats the best answer!

Fullflush

Put a sail on the boot and hope the wind is blowing the correct way

StephTell

There must be something in it because I drive quite a bit faster and more 'sporty' (for lack of a better word) than the missus but the cars run a lot more frugal when I'm behind the wheel...so that must mean I'm more efficient with accelerating/braking or my shifting is better i.e. ideal moment

Straight_4_N/a

Neither lol.
if you live where I am you can roll for 5 miles and no need to touch the throttle and still brake the speed limit lol.

Option C.
stick the car in snow mode and drive how ever you like you cant open the throttle all the way anyway lol.