With the rising price of petrol and the amount of motorway miles I do, I'm nervously watching my MPG figure at all times. I drive a naturally-aspirated 1.2 (not sure if it's the 60HP or 70HP model) and even curbing my highway speed and driving carefully, struggle to best 50mpg average at 55mph (on a good bit of road in good weather, I can hit 60-65mpg at 55-60mph but never sustained over v long distance).

My average city mpg is usually 30-35mpg with a lot of stop-start, 40-45mpg with good traffic flow, and touching 50mpg if there's a mix of 40mph roads, for an idea of my driving style. I drove about 5000 miles last year and this year might hit over 10,000.

 

I've been toying with "what if I just had a 6th gear" for a while, and looking this morning found a bunch of BRISOKDA articles about gearboxes. Apparently the MkII and later 6-speeds don't actually have a long ratio 6th, just an extra "2.5th" gear which wouldn't be useful to me.

Supposedly, the MkI VRS has a long-ratio 6-speed.

 

I know very little about cars - if I could get ahold of a MkI VRS 6-speed gearbox with the long 6th (there seem to be plenty about on eBay, but no information on their ratios), would it work as a drop-in replacement? Is it even compatible with a MkII 1.2?

And crucially, would I actually see any benefit, or am I misunderstanding the benefit of a long 6th?

 

Obviously, I'm spending £250 plus labour (no way am I installing this myself) in the hopes of saving maybe £30pcm in fuel, but every little helps I guess. So even if I have got it right, I know I'm not chasing a miracle.

 

Thanks guys.

The ratios for a turbo diesel's gearbox probably won't suit the 3-pot petrol I fear, to the point of being very awkward to drive in the lower gears. Gut feeling.

I doubt the bolts holding bell-housing to engine will match up either. Careful scrutiny of photos of ebay gearboxes of each type may shed some light on this.

I very much doubt you'd see a £30pcm saving either.

What tyre pressures do you use?

 

 

 

Maybe narrower more eco bias ditch finder tyres with less grip / friction and set at a higher tyre pressures and driven with great care will save a bit of fuel. That is when replacement tyres are required.

11 minutes ago, Breezy_Pete said:

The ratios for a turbo diesel's gearbox probably won't suit the 3-pot petrol I fear, to the point of being very awkward to drive in the lower gears. Gut feeling.

I doubt the bolts holding bell-housing to engine will match up either. Careful scrutiny of photos of ebay gearboxes of each type may shed some light on this.

I very much doubt you'd see a £30pcm saving either.

What tyre pressures do you use?

 

 

 

As the manual recommends 30.5psi I fill to 31psi at the pump stations (which only do whole numbers anyway). I know there's wiggle room about that for higher pressure to higher fuel efficiency but as I don't know what is safe (to not over-pressurise tyres), I don't go any further than that.

I think you can safely go quite a bit higher, but I will not give an exact number. I usually go to 2.3bar on fronts and a little more on rears on our similar cars.

1 minute ago, Breezy_Pete said:

I think you can safely go quite a bit higher, but I will not give an exact number. I usually go to 2.3bar on fronts and a little more on rears on our similar cars.

Why higher pressure on the rears? Is it because a higher pressure will lead to less road contact, and therefore the lower pressure on the front drive wheels (and steering wheels) improves grip and control?

There isn't a six speed gearbox that will fit the 1.2 three cylinder engine.

As @Breezy_Petesays, the key to more mpg lies with the tyres, you need to fit the narrowest tyres with the largest diameter that will fit and not foul, then pump them up nice and hard, 2.5 bar to start with and see how you go from there.

41 minutes ago, sepulchrave said:

There isn't a six speed gearbox that will fit the 1.2 three cylinder engine.

As @Breezy_Petesays, the key to more mpg lies with the tyres, you need to fit the narrowest tyres with the largest diameter that will fit and not foul, then pump them up nice and hard, 2.5 bar to start with and see how you go from there.

😭

Is it physically incompatible ie mounting or shaft dimensions, or is it just not practical due to how the engine physically runs?

 

So would you recommend 34psi front and 36psi rear to start?

You could try that pressures, then let down a little at a time if they do not feel OK / Safe.

 

But then nobody knows what tyres you have, brand, size etc.  

37 minutes ago, MPGwatcher said:

😭

Is it physically incompatible ie mounting or shaft dimensions, or is it just not practical due to how the engine physically runs?

 

So would you recommend 34psi front and 36psi rear to start?

 

The 1.2 3 cylinder engine was developed in-house by Skoda engineers using the gearbox found in small engined VAG economy cars, there were no six speed variants of this gearbox made at all AFAIK.

11 minutes ago, sepulchrave said:

 

The 1.2 3 cylinder engine was developed in-house by Skoda engineers using the gearbox found in small engined VAG economy cars, there were no six speed variants of this gearbox made at all AFAIK.

 

Nail on head... and all that.

 

The 1.2 could have benefitted from a longer ratio or extra gear as the droning at 60-70ish mph coming from the engine does get quite annoying eventually. One of the biggest factors in wanting/planning to change my car too.

...but fitting larger diameter tyres has the same effect as changing the final drive ratio, therefore making all the gears taller and yielding greater fuel economy in conjunction with higher pressures.

There used to be a six speed conversion kit for the Mkl 1.9TDi PD100 gearbox - basically you could add an extra cog for a sixth gear.

IIRC some 1.4TDi owners swapped the fifth gear cog for a longer ratio cog using a Darkside conversion kit. 

No idea if something like that is available for the 1.2. 

1 hour ago, sepulchrave said:

...but fitting larger diameter tyres has the same effect as changing the final drive ratio, therefore making all the gears taller and yielding greater fuel economy in conjunction with higher pressures.

...but what about town/city stop, start driving.

 

😁

Edited 22 June, 20223 yr by nta16
forgot the smiley

MPGwatcher economic driving is knowing more about driving than deeper mechanical.  Start with the basics like tyres, the unneeded weight the car carries all the stuff and advice you'll find on AA/RAC type sites and the specialist hypermiling sites.  Training yourself to drive more economically and preparing the vehicle for economic driving will also be the most cost effective methods.

 

I'd recommend that you don't trust petrol station tyre pressure gauges and buy a good quality one of your own, doesn't have to be expensive, also don't rely on the car's (especially with a VW) mpg figure but work it out yourself by how many litre it takes to fill the car's tank from the last fill and divide by the trip mileage.  The speedo/trip may be very slightly out but the error will be reasonably consistent and petrol pumps should be near enough - unless you are trained to do this professionally with professional equipment you have to accept things aren't laboratory precise.

 

There's no magic pills, mainly just the basics that have been about for years.

 

If using a Multi National owned or independent filling stations Inflation device that you pay, 20 or 50 pence or even £1 to use i trust it.

I check it with some Tyre Pressure Gauge i have but really the Fore Court maintenance is better than i am. 

 

As for a hose with an inflator coming out a door from the compressor and wrapped around a wheel bolted to a wall and free to use, i never see many of those these days.

I have no experience with this engine so I had to look it up to get an idea of the specifications.

The official figures (rounded) are city 39 mpg, urban 63 mpg, and combined 52 mpg. Power 60 or 70 bhp, torque 109 - 111 Nm (at 3000 rpm) and 0-60 between 14 and 16 seconds.

 

From your consumption figures I'd say you are a little off what they could be, possibly giving away about 5 mpg? But the urban figures are usually la la land so if you getting around the combined figures on a run then that is not too bad.

With the limited torque available I don't think a longer gear is really going to help much. On the plus side the torque comes in at relatively low revs for a small capacity NA engine so what does that 3k revs correspond to in speed in top gear?

Max torque revs are usually where the engine is most efficient, although not necessarily where it is most economical.

Unless you can get confirmation from someone that an extra and higher gear can get you quantifiably better economy, then it is difficult to justify the expense or effort.

 

Sound advice from others about increasing your tyre pressures. I actually think that 30 psi is too low and 36 psi all round will make the ride a little firmer but you will actually feel the car roll along better. You can always fine tune  pressure to your liking.

Make sure the correct maintenance schedule is adhered to, take out any unnecessary weight you are carting around and look up the road to anticipate traffic and reduce unnecessary braking or accelerations. Done correctly it does not affect others and will make a significant improvement to consumption, especially in urban areas, but you don't seem to be doing to bad at the moment truth be told.

The turbo Fabia are definitely more economical, I was very impressed by the loan 1.0tsi manual Fabia we had for a week.

 

My wife drives our Octavia but my runabout is a 2003 Toyota Echo 1.3L manual which is quoted as having a little more performance and a slightly worse consumption than yours but my overall returns are similar to what you are quoting for different scenarios. The killer for me is the large number of short runs from cold starts that it does, but my monthly mileage is relatively low so the extra cost is bearable and I still spend more on local road tax and insurance than on fuel in a month. At least there is no further depreciation costs possible on mine  

Edited 22 June, 20223 yr by Gerrycan

14 minutes ago, roottoot said:

I check it with some Tyre Pressure Gauge i have but really the Fore Court maintenance is better than i am. 

You've lost me with that - but I've not used a petrol station tyre pressure gauge for I don't know how long, probably decades, I'm too tight and grouchy old man to queue to test a petrol station gauge.

 

Let's try another angle then.  Better to have consistency with your readings, taken when the tyres are 'cold' rather than warmed from driving (unless the petrol station is close) and using the same gauge each time rather than different gauges.

 

Increasing the tyre pressures on my wife's Fabia Mk3 makes a noticeable difference to the rolling resistance on the tyres, also to the handling, never checked the mpg figures for this but would expect it to help with MPG.

 

Again the big difference is going to be from the driver and/or the way they drive, and this can be transferred to similar vehicles.  Vehicle selection would help and perhaps not following the crowd with vehicle fashions, though some of that is hard to avoid.  Of course greater concern about mpg is often in fashion when there are fuel crisis and follows the circle of fashion as those old enough have seen a few times (even if they can't remember the details).

   

The reason many use a filling station 20 pence tyre inflator even at 20 pence for the front and 20 for the rear is because they check and adjust pressures regularly car loaded, car unloaded, car towing etc, season change etc.

Easy and quick and accurate and if you have one foot or bad knees a foot pump is not ideal or a hand pump or any such.

22 minutes ago, Gerrycan said:

I have no experience with this engine so I had to look it up to get an idea of the specifications.

The official figures (rounded) are city 39 mpg, urban 63 mpg, and combined 52 mpg. Power 60 or 70 bhp, torque 109 - 111 Nm (at 3000 rpm) and 0-60 between 14 and 16 seconds.

 

From your consumption figures I'd say you are a little off what they could be, possibly giving away about 5 mpg? But the urban figures are usually la la land so if you getting around the combined figures on a run then that is not too bad.

With the limited torque available I don't think a longer gear is really going to help much. On the plus side the torque comes in at relatively low revs for a small capacity NA engine so what does that 3k revs correspond to in speed in top gear?

Max torque revs are usually where the engine is most efficient, although not necessarily where it is most economical.

Unless you can get confirmation from someone that an extra and higher gear can get you quantifiably better economy, then it is difficult to justify the expense or effort.

 

Sound advice from others about increasing your tyre pressures. I actually think that 30 psi is too low and 36 psi all round will make the ride a little firmer but you will actually feel the car roll along better. You can always fine tune  pressure to your liking.

Make sure the correct maintenance schedule is adhered to, take out any unnecessary weight you are carting around and look up the road to anticipate traffic and reduce unnecessary braking or accelerations. Done correctly it does not affect others and will make a significant improvement to consumption, especially in urban areas, but you don't seem to be doing to bad at the moment truth be told.

The turbo Fabia are definitely more economical, I was very impressed by the loan 1.0tsi manual Fabia we had for a week.

 

My wife drives our Octavia but my runabout is a 2003 Toyota Echo 1.3L manual which is quoted as having a little more performance and a slightly worse consumption than yours but my overall returns are similar to what you are quoting for different scenarios. The killer for me is the large number of short runs from cold starts that it does, but my monthly mileage is relatively low so the extra cost is bearable and I still spend more on local road tax and insurance than on fuel in a month. At least there is no further depreciation costs possible on mine  

 

 

 

 

 

70mph is at 3200rpm, so I guess 3000 is close to 65mph (34/75, 36/80 etc).

 

While it is right in the power band so performance accelerating between 60-80mph is fine, she can get thirsty.

 

I'm a fairly inexperienced driver (18mo/29), but I get the principles of economical driving - living in Birmingham is giving me road rage though, lots of inconsiderate driving which ruins trying to drive economically (and an absurd number of traffic jams). I was much happier out in semi-rural South Yorkshire!

 

I won't claim to be "good" at economical driving and often find myself with an absent minded lead foot.

I feel an economy-focused cruise control should be very simple to programme - falling latch sensor to drop fuel until revs stabilise to maximise fuel efficiency, since it's easy to flex my toe without changing speed, and suddenly boost mpg by like 10, because I've been a hair heavy on the pedal.

 

35mpg is on a REALLY bad day, with medium-bad traffic, 39 is actually a really common figure for me. Plenty of days I can get lucky with a 42-44mpg run to work 

Self-impose a 60mph top speed limit and you'll save a fair bit of fuel.

Economy looks Bob on.  As one might expect.

 

@MPGwatcher You say lots of stop-start traffic, so do you have Stop / Start on your car and do you have it enabled sometimes and off at other times?

4 hours ago, Breezy_Pete said:

Self-impose a 60mph top speed limit and you'll save a fair bit of fuel.

I have done (unless I'm late). Results weren't as good as I hoped - tried it on the 150mi journey to my parents, I was averaging 65mpg all the way north on the M42/M1, but once I got onto the M18/M180, it tanked to 50mpg no matter what I did. Running 55-60mph the whole journey.

 

On the return journey, the same - 50mpg or less until I hooked South, and suddenly it went back up.

 

Journey average both was, 50-52mpg - barely better than keeping a steady 70.

 

4 hours ago, roottoot said:

Economy looks Bob on.  As one might expect.

 

@MPGwatcher You say lots of stop-start traffic, so do you have Stop / Start on your car and do you have it enabled sometimes and off at other times?

Not part of my car's spec I'm afraid! Sits there idling 😭 I heard years ago that leaving the car in gear clutch down uses little to no fuel, and a (tiny) amount of fuel in neutral.

50-52mpg out of a 1.2 HTP Fabia is still bloody good, IMO/IME.

Strong winds make a big difference, always worth taking notice on a single journey computation. 

Whole tank brim to brim averages are much more reliable.