Fuel Economy.

[Wagger]

Firstly, don't laugh, I know that I have a 2500cc straight six and should not expect economy, however. I have owned a 2.7 litre straight six that did 37 mpg on petrol.

There have always been articles written on this topic with the best suggested speeds etc. I was told, long ago, to drive with the rpm as close as possible to maximum torque, as that is where the engine is most efficient. However, this is between 50 and 60 mph on my old cars, but more like 70 to 80 on the moderns. The last 3 diesels had max torque at 1800 rpm corresponding to road speeds of 65 to 70 mph.

I was also told to choose a car with an engine that has a long stroke, high compression and uses high octane fuel.

In year 2000, a work colleague was buying Tetra-Ethyl-Lead for his classics. That is no longer available. However, I believe that it is still used in AvGas. Correct me if I am wrong.

There are now people working on converting ICE's to run on Hydrogen. However, if they still take in air, it does not solve the Nitrogen polutants in the exhaust. Carrying Hydrogen and Oxygen in separate tanks would be essential, but still dodgy in an accident.

OK, I am in pain and bored again, but just wondered what is going on in the brains of others on this topic. Diversion therapy again.

 

[PeteH]

Fuel "efficiancy" is a thorney issue at best, getting the best from any i/c engine has many facets, not just those asociated with combustion. there is the question of mass/power ratio, friction elements, braking etc; come into the equation.

One element is driver anticipation, slowing by deceleration not brake use?. Yet the "modern" teaching has students, "braking to a stop". I look to continue progress, lift off and if clear, into the turn without a stop. Matching the "economic" RPM to road speed via the gear ratios in use at any given time, something not always possible with automatic gearboxes.

Pete.

[Pete Lewis]

the best way to improve economy is to stick a brick under the pedal not apply one to it  Ha !!

Pete

[cliff.b]

If economy is the desired outcome then driving style has a massive impact.

I have often practiced what is now called "hypermiling" for at least 30 years and have consistently found that I can get 20% more mpg by using methods that don't really hinder progress and in extreme cases about 30%. One example of the latter was a 105 mile trip in an old 1.8 petrol Vectra which returned 52mpg, as I was bored of having to keep making the journey and set myself the task of achieving it with 2 gallons of fuel. 

 Driving that car as most people normally would it typically returned about 37 to 39mpg

[Wagger]

Being lazy and using cruise on my modern gives me 52 mpg. If I don't use cruise and allow it to attain 77 down hills and not allowing it to drop below 70 I can get 56 mpg. That is over a 200 mile run. I'll have to find a way of fitting am mpg meter to the Vitesse. On a MM, I set a circuit up to count the petrol pump pulses. It sort of worked but very difficult to calibrate to real figures. The meter on the modern is within 1% of what I calculate when filling to the neck.

[68vitesse]

I have fitted a big magnet to the front of my car, but with more plastic being used in vehicles these days do not find as usful.

Regards

Paul.

[dougbgt6]

2 hours ago, Pete Lewis said:

the best way to improve economy is to stick a brick under the pedal not apply one to it 

I've a pedal stop on my accelerator and with my new super thick carpet overlapped underneath it I find I'm not going very fast.

What should I do Dr Pete?

I've a vacuum gauge, I'm told if I keep the needle steady in the middle I will achieve incredible economy. Sadly, it's main purpose has become entertainment, whizzing from one side to the other.

Doug

[PeteH]

Most moderns, calculate the MPG by recording the actual agregated amount of fuel delivered to the individual injector`s, via the ECM, and the miles recorded. Difficult to replicate on a non computer controlled/carburated vehicle I would hazard?. The accuracy of the fuel tank level recorder would impact on any calculation from that source. I seem to recall, we had flow meters, which used a venturi to estimate flow rate on some marine engines, but again the accuracy was a bit suspect. In general our consumption`s where calculated by recording fuel used over time, by the time honoured method of "dipping" (ullaging) tanks. (Tons/day). Similar to "brim to the neck", I calculate the consumption of the Campervan, using the same, Morrisons, garage and pump, and take the fill to the cut off. It`s about as accurate as you will get I expect?.

Pete

[Wagger]

The old Morris Minor electric pump would deliver a pint in an approximate number of pulses.  Sorted that, but trying to make a scale for a meter drove me bonkers. Then, the pump needed swapping so it was 'Start again'.

[Pete Lewis]

11 hours ago, dougbgt6 said:

I've a vacuum gauge

tis unfortunate but driving with the needle in the economy zone gives  un inspiring driving ( means slow)

just not compatible with a GT6  but anything below 5 hg" is wasting fuel    but makes you feel good 

do make sure the vac pipe is restricted to give a smooth needle or you get too much needle waver/vibrations 

Dr Pete 

[Pete Lewis]

my 82 Solara had a trip consumption display  guess it used flow /return and tank level  

my supervisor used it to visit a dealer and tried hard and managed to get it under 4mpg  

Pete

[68vitesse]

When I set the moderns display to MPG and set the cruise control I was surprised by how small a hill was required to make a large difference to the consumption, and accelerating out of roundabouts could get down to single figures.

Regards

Paul

[Colin Lindsay]

17 minutes ago, 68vitesse said:

When I set the moderns display to MPG and set the cruise control I was surprised by how small a hill was required to make a large difference to the consumption, and accelerating out of roundabouts could get down to single figures.

Regards

Paul

On my Volvo, when decelerating, the 'instant fuel consumption' used to register 999 mpg. Sadly when accelerating it used to drop to about 6.

[Clive]

8 minutes ago, Colin Lindsay said:

On my Volvo, when decelerating, the 'instant fuel consumption' used to register 999 mpg. Sadly when accelerating it used to drop to about 6.

Yep, fuel injected cars shut the fuel off when decelerating. All clever stuff, I tried mapping my spitfire to do that, but couldn't get it to work well.

[PeteH]

An interesting facet of modern fuel consumption "live" metering, is one I encountered locally. The L-A in their "wisdom". dropped the A1035, from National limit, to 50mph. and of course the local plod`s where having a Field day. ££££££££`s in fines. What I discovered was the my then modern, Diesel/Auto which would return close to 60mpg at 60mph in 6th gear, using the limiter. However, If I stuck to 50mph, again on the limiter, the `box would not change into 6th. staying in 5th, this increased the fuel consumption, down to 52mpg. Not believing it at first, I conducted trials, once plod had lost interest, and sure enough, what I thought was happening was repeatable. Same section of road, similar conditions and over several runs. Had the car not been due for replacement. I was looking into getting the box reprogramed by the dealer?.

So, Reducing the speed limit was actually costing me at the pump!!!.

Pete

[NonMember]

5 minutes ago, PeteH said:

So, Reducing the speed limit was actually costing me at the pump!!!

It happens. During one of the fuel crises (possibly the 1973 one?) several countries imposed lower speed limits "to save fuel", and more than one of these was found to actually increase fuel consumption because the cars were now too far from their optimal operating region.

[Wagger]

I had that problem with my 'Automatics'. No lockup on the lower gears originally, now most do this but any touch on the 'Loud' pedal and they go into 'Slip' mode.

I believe that the most efficient gear on a manual box is the 1:1, so my six speed manual has two overdrive gears. Quite how inefficient they are, I have no idea. Top still gives engine braking until the slope exceeds 1 in 12. The autos did not have any real braking on the overun but changed down in an attempt to maintain cruise.

Some cars had a freewheel (Even 1970's SAAB) so, is that legal if fitted as standard?

[Chris A]

19 minutes ago, NonMember said:

It happens. During one of the fuel crises (possibly the 1973 one?) several countries imposed lower speed limits "to save fuel", and more than one of these was found to actually increase fuel consumption because the cars were now too far from their optimal operating region.

Yes my Skoda can be more fuel efficient at a higher, but still legal, road speed than when on sections with lower limits. The car must be geared to be more efficient at what the constructor thought would be normal cruising speed. When the limits here were reduced to 80 it was a real pain! Car will cope with 80 in 5th but with all the hills around here it was regularly necessary to drop to 4th and fuel consumption went up! Must add that the restriction wasn't a fuel saving measure but aimed at reducing accidents & injuries.

[NonMember]

1 hour ago, Wagger said:

I believe that the most efficient gear on a manual box is the 1:1

That depends on the box. It's true of the Triumph boxes, because 4th (the 1:1 gear) is direct and therefore has no gear mesh losses. Many a modern FWD car has a complete box full of indirect gears, so the efficiency isn't noticeably different between them.

1 hour ago, Chris A said:

The car must be geared to be more efficient at what the constructor thought would be normal cruising speed.

Quite often the car is geared to be most efficient at the speed that the regulators pick for homologation (and hence published) measurements.