ok, so i know that the tendency is for posts on this forum to be about how much you can thrash the nuts off the car and how much power you can squeeze from the 1.9 litres of sooty engineering.

BUT, has anyone any idea as to the most economical number of revs that the engine needs to get the most from a single gallon of diesel??

i originally thought that the lower the revs , the more economical, but now i'm not so sure....

now this is gonna sound really sad but i'm still new to this diesel business and am still playing with the car in many ways including trying to get decent mpg on boring trips by watching the trip computer (beats competitions to see who can keep a polo mint in their gob, without breaking it ,the longest believe me!)

i honestly think that the ideal would be somewhere around 2200 or summat . i cannot explain why but it doesnt seem that the lower the revs the more economical the engine. has anyone else looked into this or has anyone else any (more concrete) ideas?

i'm really quite an interesting person outside of this thread!

I would presume around the 2000rpm mark... the engine is at its most efficent (peak torque).

maybe to do with not letting the engine struggle in a high gear ?

mines just a smidge under 2500rpm which matches peak torque on the rolling road. Thats about 80mph in 5th!!!

I try not to drop below 2k

Seems to destroy the MPG if you do let it drop below 2k

Whats MPG? :confused: I managed to get under 30mpg on my journey home yesterday! Have to say I was having some fun.

I've had it down to 26 MPG before

I was having fun too

Agree with mobtob, letting the revs drop below 2k seems counterproductive in that respect.

perhaps we should have a new thread related to who got the least mpg on a decent run!

anyone got photographic evidence of low mpg on ,say, at least a 20 mile run?must be a reasonable length of run cos any muppet can get a reading of less than 20 if they boot it from cold.

have noticed that (obviously) the mpg starts to reduce whilst sitting stationary in traffic -has anyone got a negative value??? (perhaps those who use the redheugh bridge to get to work will be the best to ask, or our m25 friends??)

so glad i bought the diesel now with the oil price going through the roof - can still have fun and yet doesnt cost any more than 'driving miss daisy' in me old petrol motor.

My Superb has just done a trip to Devon and back, along with travelling around the area for a couple of days...tank so far is on 630 miles with a computer reading of 52.5 mpg. Thats with the pd130 under the bonnet.

Edit: I should add that the cruise was set at 70, and we did the M25,M3,A303,M5,A303 then pottering round town and country. Then returning home was the complete reversal however cruise was cancelled on the M25, and loud pedal fully engaged until home. (70 equates to around 2200 rpm in fifth)

what was your average recorded speed on the trip computer? were you sat in 6th most of the way- what revs do you think you were at? is it the same gear ratios as the fabia? if so we can get closer to finding the 'ideal' rev value for mpg.

Surely most economical will be when the turbo isn't being used? My mpg goes up massively if I'm cruising along at 40mph in 5th gear, with the revs at about 1200rpm.............

Chris

My best to date for a full tank is 64.5 MPG, driving on the motorway, in sixth at indicated 70. And the worst MPG to date in this one? 16 MPG for a full tank

AFAIK the fuel consumption has more to do with throttle position than engine revs. So if you're using low revs and labouring the engine then chances are you'll have your foot harder on the throttle than if you dropped down a gear, hence economy will suffer...

Rob.

IIRC, someone posted an mpg of 111.something last week (can't remember who, though!), which would be a pretty good target!

If the rev counter on a Volvo truck is anything to go by, best efficiency is mid-revs - the counter is coloured orange up to 1500 rpm, green from there to about 3000 rpm, orange again up to 5000 rpm, and then red (obviously!) at 5000 rpm. I'm not sure whether something similar would apply to my Furby (ain't had the chance to test the theory yet), but scientifically speaking, an engine is most efficient at high revs, but only up to the point where vibration and friction in the drivetrain starts to slow things down again. I shouldn't think the turbo would kill the economy too badly, as although it will reduce the efficiency of the exhaust system, the boost provided by it compressing the fuel-air mix going into the cylinder would more than outweigh it, I reckon.

Could be wrong, though...

PS: The 'drive by wire' throttle on the Furby limits the throttle opening anyway, I think, so even if you stomp really hard on the pedal, you won't get full throttle straightaway - it's an emissions reducing thing more than anything else, but obviously helps the fuel economy some. It can ony do so much though, so driving in too high / too low a gear is going to mess things up, as Rob's just said!

I reckon only full tank figures should count

When you have loads of power it is not easy to see the real enemy of mpg which is wind resistance.

You see it on bikes clearly when a 50cc 6hp machine can do 55 whereas a 100cc 12hp will do around 65-70. Wind resistance increases with the square of forward speed which means that the bike doing 65 is coping with over twice the resistance for a small increase in speed.

In oridinary terms wind resistance is light till about 55mph and builds rapidly thereafter.

In a fab vrs or similar it seems so effortless that we can convince ourselves that ,say, 80mph and 2300rpm would give best economy - very wrong.

Now the gearing won't help us here but the best economy will be at modest revs and throttle openings at LOW speed. This in practice would be hard work as the vrs has high ratios, paradixically best mpg would be at 40 or so mph and having to use 4/5 and (it won't like it) 6th where and when you can.

The best way to get hyper mpg.

Most VRS drivers will choose to ignore this post ....after all course this is all against Briskoda philosophy - apologies...

1. Avoid unneccesary braking. Braking represents energy loss. :( So try and plan ahead. Anticipate when you need to slow down or stop and allow the car to decellerate by itself (or better still coast) until the desired point. Unfortunately this means a very long braking period which might frustrate other drivers but over that long period you are saving lots of fuel...if you can keep rolling at constant(ish) speed then thats even better.

2. Avoid unnecessary acceleration. Its best way is to use cruise control (if you have it). Try and avoid frequent minor changes in accelerator position (which is difficult). The best way I find is to steady your foot on the right edge of the footwell and the pedal thereby reducing the tendency to wander (power wise).

3. When accelerating - try to accelerate through the gears at about half the max available acceleration. Don't floor it but more importantly don't be a slouch and hang about in the lower gears. Long drawn out slow acceleration through the gears uses far more fuel than a smart (but not full out) one. Again the cruise control has an optimum acceleration when you apply the button. The exception to this rule is top gear. In top gear always acelerate gently.

4. Going up the gears change up so your revs never drop too low (for a Tdi around 1700 rpm) slogging the engine (for acceleration) is inefficient. Avoid very high revs (above 3000 rpm) though this is not so important.

5. Most importantly of all, hyper mpg is easy if you cut your top speed. Drive a Tdi at under 55mph and you will get sky high figures.

6. If you choose to dawdle along in a high gear at low revs (say under 1400 rpm) - be gentle with the accelerator - max torque here is not very efficient but low torque is.

Using this simple guide and you should easily top 70mpg for diesel Fabias and even 55mpg for diesel Galaxies (average figures).

In terms of importance, point 5 is first, point 1 is second.

You forgot one thing...let cruise take over, then you get real good mpg.

Cruise control is the best way - its acceleration pattern in particular is optimal.