Am trying to reconcile the fact that one car that runs at low rpm has worse fuel consumption than one with a similar engine that runs at higher rpm. Both are EFI, neither has any form of turbocharging or supercharging.

Car 1. 1.6 L engine, runs at 2100 rev/min at 100 km/hr and gets 6.9 L/100 km.
Car 2. 1.5 L engine, runs at 2900 rev/min at 100 km/hr and gets 6.1 L/100 km.

1 hr = 60 min, use 740 and 1.2 kg/L for densities of fuel and air, and two revs per engine volume.

That’s all the information needed to get air-fuel ratio. I get:
Car 1. Air-fuel ratio = 22.7:1
Car 2. Air-fuel ratio = 33.7:1

That’s a big difference. Is that what you get? Does that look reasonable or are some of the car gauges reading wrong?

stroke, and possibly total cylinder (including head/chamber) displacement, + cam/intake/exhaust timing….maybe

mollwollfumble said:

Am trying to reconcile the fact that one car that runs at low rpm has worse fuel consumption than one with a similar engine that runs at higher rpm. Both are EFI, neither has any form of turbocharging or supercharging.

Car 1. 1.6 L engine, runs at 2100 rev/min at 100 km/hr and gets 6.9 L/100 km.
Car 2. 1.5 L engine, runs at 2900 rev/min at 100 km/hr and gets 6.1 L/100 km.

1 hr = 60 min, use 740 and 1.2 kg/L for densities of fuel and air, and two revs per engine volume.

That’s all the information needed to get air-fuel ratio. I get:
Car 1. Air-fuel ratio = 22.7:1
Car 2. Air-fuel ratio = 33.7:1

That’s a big difference. Is that what you get? Does that look reasonable or are some of the car gauges reading wrong?

Air resistance?

the torque/efficiency/RPM curves, and gear ratios

transition said:

the torque/efficiency/RPM curves, and gear ratios

Tyre pressures.

Tamb said:

transition said:

the torque/efficiency/RPM curves, and gear ratios

Tyre pressures.

Engine efficiency – I am guessing two different manufacturers? One has more power?

Have you confirmed:
Measured speed is correct (I bet this is between 5-10% high on at least one of the vehicles)
Measured distance is correct.
Displayed fuel economy is correct.

Are both vehicles in the same gear, same diameter tyres?

The smaller engine has to work a lot harder to get up to 100kph, at 60, the fuel efficiencies would most likely be reversed.

eg, a prius running full pelt around a track uses more fuel than a BMW 3 series running at a cruising speed (for it’s motor) to just keep up to it (top gear ref, so probably a but sensationalised, but you get the point)

Fwiw when Holden put a four cylinder into the commodore (star fire?) the resulting car was both not as powerful and had worse fuel economy than the six.

That overall fuel air mixture is over the cycle, the higher revving one might be in an operating sweet spot. Most engines have one.

the compression ratios, and stroke and piston diameters for start be helpful

Carmen_Sandiego said:

Tamb said:

transition said:

the torque/efficiency/RPM curves, and gear ratios

Tyre pressures.

Engine efficiency – I am guessing two different manufacturers? One has more power?

Have you confirmed:
Measured speed is correct (I bet this is between 5-10% high on at least one of the vehicles)
Measured distance is correct.
Displayed fuel economy is correct.

Temperature/air density/humidity make a big difference.

related

http://en.wikipedia.org/wiki/Lean_burn

A lean burn mode is a way to reduce throttling losses. An engine in a typical vehicle is sized for providing the power desired for acceleration, but must operate well below that point in normal steady-speed operation. Ordinarily, the power is cut by partially closing a throttle. However, the extra work done in pumping air through the throttle reduces efficiency. If the fuel/air ratio is reduced, then lower power can be achieved with the throttle closer to fully open, and the efficiency during normal driving (below the maximum torque capability of the engine) can be higher.

The engines designed for lean burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low exhaust hydrocarbon emissions than those found in conventional petrol engines. Ultra lean mixtures with very high air–fuel ratios can only be achieved by direct injection engines.

Also, what age are the cars?
Most cars these days have sensors that will lean of or richen up air/fuel mixtures depending on how the motor is running to get the best out of them.

You can look at fuel types as well, were both cars filled at the same servo? different brands can cause differences in mileage.

were both cars serviced recently? it’s surprising how much an oil change can alter the range of a tank of petrol, ail filter dirtl can cause a motor to run rich.

Lots of variables to play with

well your air fuel ratios are wrong. most cars work on an afr of 14.7:1.

http://en.wikipedia.org/wiki/Lean_burn

Lean burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean burn engines the air:fuel ratio may be as lean as 65:1 (by mass). The air:fuel ratio needed to stoichiometrically combust petrol, by contrast, is 14.64:1. The excess of air in a lean burn engine combusts more of the fuel and emits fewer hydrocarbons. High air–fuel ratios can also be used to reduce losses caused by other engine power management systems such as throttling losses.

At a guess, the higher revving Car 2 would have a smaller drive gearing than Car 1, which like small tyres take less energy to rotate, than large wheels, so the gearing would be more efficient to move Car 2 than Car 1.

You’re assuming 100% volumetric efficiency when making your calculation of the volume of air drawn into the engine. A 1.6 litre engine doesn’t necessarily draw in 1.6 litres of air/fuel every 2 revolutions.

pommiejohn said:

You’re assuming 100% volumetric efficiency when making your calculation of the volume of air drawn into the engine. A 1.6 litre engine doesn’t necessarily draw in 1.6 litres of air/fuel every 2 revolutions.

Yeah, that was what I was trying to say.

AwesomeO said:

pommiejohn said:

You’re assuming 100% volumetric efficiency when making your calculation of the volume of air drawn into the engine. A 1.6 litre engine doesn’t necessarily draw in 1.6 litres of air/fuel every 2 revolutions.

Yeah, that was what I was trying to say.

Oh yeah, I should have read the thread better.

it would be good to know what the motors are. there may be issues with the design that compromises fuel efficiency. plus gearing, final drive etc. body type. gross mass.

Boris said:

it would be good to know what the motors are. there may be issues with the design that compromises fuel efficiency. plus gearing, final drive etc. body type. gross mass.

There are too many variables between two cars to make meaningful calculations about fuel consumption IMHO.

pommiejohn said:

Boris said:

it would be good to know what the motors are. there may be issues with the design that compromises fuel efficiency. plus gearing, final drive etc. body type. gross mass.

There are too many variables between two cars to make meaningful calculations about fuel consumption IMHO.

Yesterday on xtreme 4 we’d they raided the fuel consumption of an old Dodge Ram from 8 mpg to 14 mpg, a lot of that was down to reducing weight.

Why two exact cars can have varying fuel efficiency

Car millage, wear & condition (engine & driveline)

Engine oil used & condition

Spark plugs used & condition

Condition of fuel system (injectors, filters, pump, etc.)

Tyre type, condition, pressure, alignment

Condition of suspension

Condition of cooling system

Weight of vehicles at time of testing

There probably the main ones

The_observer said:

Why two exact cars can have varying fuel efficiency

Car millage, wear & condition (engine & driveline)

Engine oil used & condition

Spark plugs used & condition

Condition of fuel system (injectors, filters, pump, etc.)

Tyre type, condition, pressure, alignment

Condition of suspension

Condition of cooling system

Weight of vehicles at time of testing

There probably the main ones

Quality of the fuel varies

wookiemeister said:

The_observer said:

Why two exact cars can have varying fuel efficiency

Car millage, wear & condition (engine & driveline)

Engine oil used & condition

Spark plugs used & condition

Condition of fuel system (injectors, filters, pump, etc.)

Tyre type, condition, pressure, alignment

Condition of suspension

Condition of cooling system

Weight of vehicles at time of testing

There probably the main ones

Quality of the fuel varies

we’ll take for granted that the fuel used for the example test is from the same pump on the same day :)

The_observer said:

wookiemeister said:

The_observer said:

Why two exact cars can have varying fuel efficiency

Car millage, wear & condition (engine & driveline)

Engine oil used & condition

Spark plugs used & condition

Condition of fuel system (injectors, filters, pump, etc.)

Tyre type, condition, pressure, alignment

Condition of suspension

Condition of cooling system

Weight of vehicles at time of testing

There probably the main ones

Quality of the fuel varies

we’ll take for granted that the fuel used for the example test is from the same pump on the same day :)

If the fuel is warm it will contract in the tank as it cools

If the fuel has water in it that could be a problem too

If you filled the two cars at the same time that would help

The_observer said:

Why two exact cars can have varying fuel efficiency

Car millage, wear & condition (engine & driveline)

Engine oil used & condition

Spark plugs used & condition

Condition of fuel system (injectors, filters, pump, etc.)

Tyre type, condition, pressure, alignment

Condition of suspension

Condition of cooling system

Weight of vehicles at time of testing

There probably the main ones

Millage was a good one. As an engine can be pulled apart and every component re-polished. This will markedly change the fuel consumption and performance. Mass produced cars have a similar problem to any mass produced items in that the cars made on any day of the week will differ slightly from the other days.
My father only ever bought one car during my lifetime with him and the day he did he started every car in the showroom and selected one. I want this one he said. I said but dad you are an old fogey, this car is the 186S version of the Kingswood. If you want a sports car why not the then new Monaro? He said simply. This one has the best balanced motor. The interesting thing was that 45 years later I talked to the Holden mechanic and out of the blue he mentioned that the car my mother was still driving, “had the best balanced motor ever to come into this town”.

with todays manufacturing techniques you can pretty well be assured that the products are very similar.

Boris said:

with todays manufacturing techniques you can pretty well be assured that the products are very similar.

Cue iRobot.

roughbarked said:

The_observer said:

Why two exact cars can have varying fuel efficiency

Car millage, wear & condition (engine & driveline)

Engine oil used & condition

Spark plugs used & condition

Condition of fuel system (injectors, filters, pump, etc.)

Tyre type, condition, pressure, alignment

Condition of suspension

Condition of cooling system

Weight of vehicles at time of testing

There probably the main ones

Millage was a good one. As an engine can be pulled apart and every component re-polished. This will markedly change the fuel consumption and performance. Mass produced cars have a similar problem to any mass produced items in that the cars made on any day of the week will differ slightly from the other days.
My father only ever bought one car during my lifetime with him and the day he did he started every car in the showroom and selected one. I want this one he said. I said but dad you are an old fogey, this car is the 186S version of the Kingswood. If you want a sports car why not the then new Monaro? He said simply. This one has the best balanced motor. The interesting thing was that 45 years later I talked to the Holden mechanic and out of the blue he mentioned that the car my mother was still driving, “had the best balanced motor ever to come into this town”.

I pulled apart the engine in a Hiace van I had once & had the components balanced at a local engineering shop that specialised in doing this.
The difference the balancing made was amazing.

>The difference the balancing made was amazing

tell me what was improved, I’m thinking of getting my B&S lawnmower engine done

transition said:

>The difference the balancing made was amazing

tell me what was improved, I’m thinking of getting my B&S lawnmower engine done

the crank, pistons & conrods, flywheel were all balanced.
The engine was smoother & quieter sounding. I changed the rings & bearings & gave
the cylinder a hone. Improved performance.

I’m not sure how this would translate to a lawn mower

>the crank, pistons & conrods, flywheel were all balanced.
The engine was smoother & quieter sounding.

Isn’t combustion sort of lumpy and varied anyway?

transition said:

>the crank, pistons & conrods, flywheel were all balanced.
The engine was smoother & quieter sounding.

Isn’t combustion sort of lumpy and varied anyway?

consider the effect balancing has on car wheel & tyre assembly

>consider the effect balancing has on car wheel & tyre assembly

no worries, I’l get my lawnmower motor balanced at the local tyre shop.

transition said:

>consider the effect balancing has on car wheel & tyre assembly

no worries, I’l get my lawnmower motor balanced at the local tyre shop.

you do that, then mow their driveway for them

On one of the arvo car tuning shows they were showing a fellow porting and polishing ports. On the intake side smoothing out the castings and more importantly opening the port up to the gasket dimensions added about 11cc to each intake.

The_observer said:

transition said:

>consider the effect balancing has on car wheel & tyre assembly

no worries, I’l get my lawnmower motor balanced at the local tyre shop.

you do that, then mow their driveway for them

Did anyone watch the “I love my car” show on TV?

There was a Cooper S that had been balanced by a company name starting with H? the guy on the show pulled the motor down and re-polished every component, renewed things like changing the radiator to modern materials.

>you do that, then mow their driveway for them

no worries, mate, might get a wheel alignment done while I’m there.

transition said:

>you do that, then mow their driveway for them

no worries, mate, might get a wheel alignment done while I’m there.

Now that would be an improvement for any lawnmower.

transition said:

>you do that, then mow their driveway for them

no worries, mate, might get a wheel alignment done while I’m there.

Ask about their range of alloy wheels for you BS

>Now that would be an improvement for any lawnmower.

yeah my push mower has no toe-in at all, and caster needs doing.

AwesomeO said:

On one of the arvo car tuning shows they were showing a fellow porting and polishing ports. On the intake side smoothing out the castings and more importantly opening the port up to the gasket dimensions added about 11cc to each intake.

?

>Ask about their range of alloy wheels for you BS

there’s a thought, while I’m near the local mechanic I might get extractors fitted.

transition said:

>Now that would be an improvement for any lawnmower.

yeah my push mower has no toe-in at all, and caster needs doing.

just bolt the BS engine onto the bottom of a shopping trolley

use it like a Flymo

transition said:

>Now that would be an improvement for any lawnmower.

yeah my push mower has no toe-in at all, and caster needs doing.

Ask for a complete overhaul of the wheel bearings.

transition said:

>Ask about their range of alloy wheels for you BS

there’s a thought, while I’m near the local mechanic I might get extractors fitted.

You have a two cylinder lawn mower?

>You have a two cylinder lawn mower?

no it’s a single, but I thought the other unconnected pipes would look intriguing

transition said:

>You have a two cylinder lawn mower?

no it’s a single, but I thought the other unconnected pipes would look intriguing

Mine has a BSA Lighting donk.

transition said:

>You have a two cylinder lawn mower?

no it’s a single, but I thought the other unconnected pipes would look intriguing

I say you should go for it.

It would inspire a poem or fifty

>I say you should go for it.

anyway, back to balance

http://en.wikipedia.org/wiki/Engine_balance

A bloke on another forum ported and polished the intake of his cloned honda engine on his mower and upgraded the fuel pump. Goes through damp/long grass like a knife through butter. Uses a tad more fuel though. :)

Carmen_Sandiego said:

A bloke on another forum ported and polished the intake of his cloned honda engine on his mower and upgraded the fuel pump. Goes through damp/long grass like a knife through butter. Uses a tad more fuel though. :)

Does he sharpen his own blades?

If you could afford one, could this be the lawnmower motor for you?

not sure what that bike is, reminds me though one my first go-karts had a BSA motorbike gearbox, 4 speed as I recall

Ariel Square Four.

1952 model, 1000cc.

roughbarked said:

If you could afford one, could this be the lawnmower motor for you?

>>>If you could afford one, could this be the lawnmower motor for you?<<<

That motorcyclist is wearing the very same model head protection I wear when ever I
mow the lawn with a Briggs n Stratton

:)

The_observer said:

roughbarked said:

If you could afford one, could this be the lawnmower motor for you?

>>>If you could afford one, could this be the lawnmower motor for you?<<<

That motorcyclist is wearing the very same model head protection I wear when ever I
mow the lawn with a Briggs n Stratton

:)

Need them on your shins too. My Briggs spun the crankshaft off and threw the whole rotor assembly out the back.. Just missed my shins.

roughbarked said:

The_observer said:

roughbarked said:

If you could afford one, could this be the lawnmower motor for you?

>>>If you could afford one, could this be the lawnmower motor for you?<<<

That motorcyclist is wearing the very same model head protection I wear when ever I
mow the lawn with a Briggs n Stratton

:)

Need them on your shins too. My Briggs spun the crankshaft off and threw the whole rotor assembly out the back.. Just missed my shins.

Obviously you’re BnS needed balancing

The_observer said:

roughbarked said:

If you could afford one, could this be the lawnmower motor for you?

!http://www.motorcycleclassics.com/~/media/Images/MCC/Editorial/Articles/Magazine%20Articles/2006/03-01/1952%20Ariel%20Square%20Four/Ariel-1CMYK.jpg

>>>If you could afford one, could this be the lawnmower motor for you?<<<

That motorcyclist is wearing the very same model head protection I wear when ever I
mow the lawn

If only Rodney had done the same thing, Bubblecar wouldn’t have to mow his lawn himself.

OCDC said:

The_observer said:

roughbarked said:

If you could afford one, could this be the lawnmower motor for you?

!http://www.motorcycleclassics.com/~/media/Images/MCC/Editorial/Articles/Magazine%20Articles/2006/03-01/1952%20Ariel%20Square%20Four/Ariel-1CMYK.jpg

>>>If you could afford one, could this be the lawnmower motor for you?<<<

That motorcyclist is wearing the very same model head protection I wear when ever I
mow the lawn

If only Rodney had done the same thing, Bubblecar wouldn’t have to mow his lawn himself.

I don’t know who Rodney was, but god rest his 4 stroke

The_observer said:

roughbarked said:

If you could afford one, could this be the lawnmower motor for you?

>>>If you could afford one, could this be the lawnmower motor for you?<<<

That motorcyclist is wearing the very same model head protection I wear when ever I
mow the lawn with a Briggs n Stratton

:)

Similar stance too?

>That motorcyclist is wearing the very same model head protection I wear when ever I
mow the lawn with a Briggs n Stratton :)

The ol’ B&S, jeeez pulled some them apart when just little kid, and assembled them from boxes of parts given me. Don’t miss it at all. Back in the day when had aluminium bore. Can’t remember the B&S having one bearing in them, not even a sleeve or bush, come some way since.

transition said:

>That motorcyclist is wearing the very same model head protection I wear when ever I
mow the lawn with a Briggs n Stratton :)

The ol’ B&S, jeeez pulled some them apart when just little kid, and assembled them from boxes of parts given me. Don’t miss it at all. Back in the day when had aluminium bore. Can’t remember the B&S having one bearing in them, not even a sleeve or bush, come some way since.

the Phantom Agents wore the same model Helmut that I wear when mowing the lawn using a Briggs N Startton mower.

Guns were their last resort, like a Briggs n Startton to mow the lawn

get the exhaust gas measured and see what percentages you get for carbon dioxide/ monoxide, all the other gases

The_observer said:

roughbarked said:

Need them on your shins too. My Briggs spun the crankshaft off and threw the whole rotor assembly out the back.. Just missed my shins.

Obviously you’re BnS needed balancing

indeed

wookiemeister said:

get the exhaust gas measured and see what percentages you get for carbon dioxide/ monoxide, all the other gases

I left that off my list -

the exhaust – modifications, condition, quality, design

the exhaust is the best indicator of performance I’d say

The_observer said:

wookiemeister said:

get the exhaust gas measured and see what percentages you get for carbon dioxide/ monoxide, all the other gases

I left that off my list -

the exhaust – modifications, condition, quality, design

probably one of the more important things to be neglected.

but then I went off at a tangent when you typed millage.

wookiemeister said:

the exhaust is the best indicator of performance I’d say

what comes out of it

wookiemeister said:

the exhaust is the best indicator of performance I’d say

extractors prove that.

roughbarked said:

The_observer said:

wookiemeister said:

get the exhaust gas measured and see what percentages you get for carbon dioxide/ monoxide, all the other gases

I left that off my list -

the exhaust – modifications, condition, quality, design

probably one of the more important things to be neglected.

but then I went off at a tangent when you typed millage.

what’s the metric equivalent of mileage ?

The_observer said:

roughbarked said:

The_observer said:

I left that off my list -

the exhaust – modifications, condition, quality, design

probably one of the more important things to be neglected.

but then I went off at a tangent when you typed millage.

what’s the metric equivalent of mileage ?

aged metres?

roughbarked said:

The_observer said:

roughbarked said:

probably one of the more important things to be neglected.

but then I went off at a tangent when you typed millage.

what’s the metric equivalent of mileage ?

aged metres?

kilometerage… sound queer

roughbarked said:

The_observer said:

roughbarked said:

probably one of the more important things to be neglected.

but then I went off at a tangent when you typed millage.

what’s the metric equivalent of mileage ?

aged metres?

anyway it slipped past like the telephone poles when they flicker like a picket fence.
by

Millage.. I meant.. the milling of the machined parts.

roughbarked said:

roughbarked said:

The_observer said:

what’s the metric equivalent of mileage ?

aged metres?

anyway it slipped past like the telephone poles when they flicker like a picket fence.
by

Millage.. I meant.. the milling of the machined parts.

balancing & polishing were mentioned a bit.

polishing is simply removing carbon build up.

there are additives available that can do that without pulling things to bits

The_observer said:

roughbarked said:

roughbarked said:

aged metres?

anyway it slipped past like the telephone poles when they flicker like a picket fence.
by

Millage.. I meant.. the milling of the machined parts.

balancing & polishing were mentioned a bit.

polishing is simply removing carbon build up.

there are additives available that can do that without pulling things to bits

You are talking to a watchmaker, mate.

Give me the tools and your car will really tick in beat.

roughbarked said:

The_observer said:

roughbarked said:

anyway it slipped past like the telephone poles when they flicker like a picket fence.
by

Millage.. I meant.. the milling of the machined parts.

balancing & polishing were mentioned a bit.

polishing is simply removing carbon build up.

there are additives available that can do that without pulling things to bits

You are talking to a watchmaker, mate.

Give me the tools and your car will really tick in beat.

I can dismantle a watch in no time flat !!

I’d just need you to put it back together again

The_observer said:

roughbarked said:

The_observer said:

what’s the metric equivalent of mileage ?

aged metres?

kilometerage… sound queer

kilométrage (no e)

http://www.collinsdictionary.com/dictionary/french-english/kilométrage

morrie said:

The_observer said:

roughbarked said:

aged metres?

kilometerage… sound queer

kilométrage (no e)

http://www.collinsdictionary.com/dictionary/french-english/kilométrage

May take the next generation to wrap their lips around that, because I’m all ears :)

I was going to by the car, but the kilométrage was outrageous.

The_observer said:

morrie said:

The_observer said:

kilometerage… sound queer

kilométrage (no e)

http://www.collinsdictionary.com/dictionary/french-english/kilométrage

May take the next generation to wrap their lips around that, because I’m all ears :)

‘fraid have only one of those.

roughbarked said:

The_observer said:

morrie said:

kilométrage (no e)

http://www.collinsdictionary.com/dictionary/french-english/kilométrage

May take the next generation to wrap their lips around that, because I’m all ears :)

‘fraid have only one of those.

>>>‘fraid have only one of those.<<<

ears??

BnS?

morrie said:

I was going to by the car, but the kilométrage was outrageous.

Thankfully I waited until the right car came up.
The kilométrage wasn’t outrageous
and by calculation I was aware that for a sixth of the least available average kilométrage, the price was outrageously cheap.

The_observer said:

roughbarked said:

The_observer said:

May take the next generation to wrap their lips around that, because I’m all ears :)

‘fraid have only one of those.

>>>‘fraid have only one of those.<<<

ears??

BnS?

the first one.

roughbarked said:

The_observer said:

roughbarked said:

‘fraid have only one of those.

>>>‘fraid have only one of those.<<<

ears??

BnS?

the first one.

blame Transition,,, his goodnight poems,,, & his love of BnS

transition said:

the compression ratios, and stroke and piston diameters for start be helpful

Not needed for the calculation. Neither are wheel diameter, air resistance etc.

Being 4-stroke engines there are always two revolutions per total cylinder volume. So given measured revs per minute at 100 km/hr and known engine volume all of “compression ratios, and stroke and piston diameters” drop out of the calculation. Similarly, given known fuel consumption at 100 km/hr, all the aerodynamic factors drop out of the calculation. Gear ratios, transmission losses and similar also drop out of the calculation. All that can possibly vary is:
1) Measurement errors, which ought to be only of order 10%.
2) Air-fuel ratio.

pommiejohn said:

You’re assuming 100% volumetric efficiency when making your calculation of the volume of air drawn into the engine. A 1.6 litre engine doesn’t necessarily draw in 1.6 litres of air/fuel every 2 revolutions.

Good. I was wondering about that. But could a 1.6 liter engine possibly draw in as little as 0.8 litres in two revolutions? That’s what would be needed to explain the high air-fuel ratio calculated for one of the cars. Wouldn’t that be a huge pressure loss on engine intake?

mollwollfumble said:

transition said:

the compression ratios, and stroke and piston diameters for start be helpful

Not needed for the calculation. Neither are wheel diameter, air resistance etc.

Being 4-stroke engines there are always two revolutions per total cylinder volume. So given measured revs per minute at 100 km/hr and known engine volume all of “compression ratios, and stroke and piston diameters” drop out of the calculation. Similarly, given known fuel consumption at 100 km/hr, all the aerodynamic factors drop out of the calculation. Gear ratios, transmission losses and similar also drop out of the calculation. All that can possibly vary is:
1) Measurement errors, which ought to be only of order 10%.
2) Air-fuel ratio.

Seems odd. Akin to saying my ute using 11L/100km vs my Lancer using 6L/100km is just down to air-fuel ratio and measurement error…

The_observer said:

Why two exact cars can have varying fuel efficiency

Car millage, wear & condition (engine & driveline)

Engine oil used & condition

Spark plugs used & condition

Condition of fuel system (injectors, filters, pump, etc.)

Tyre type, condition, pressure, alignment

Condition of suspension

Condition of cooling system

Weight of vehicles at time of testing

There probably the main ones

Not one of those has anything to do with the original question. Because all of those increase fuel consumption by increasing the revs per minute. My question was about how come lower fuel efficiency could come from lower revs per minute with nearly the same engine size. The only factor that I can think of that could do that is clogging of the air filter.

mollwollfumble said:

The_observer said:

Why two exact cars can have varying fuel efficiency

Car millage, wear & condition (engine & driveline)

Engine oil used & condition

Spark plugs used & condition

Condition of fuel system (injectors, filters, pump, etc.)

Tyre type, condition, pressure, alignment

Condition of suspension

Condition of cooling system

Weight of vehicles at time of testing

There probably the main ones

Not one of those has anything to do with the original question. Because all of those increase fuel consumption by increasing the revs per minute. My question was about how come lower fuel efficiency could come from lower revs per minute with nearly the same engine size. The only factor that I can think of that could do that is clogging of the air filter.

moll, what ages are both cars?

Most of the above will affect the air:fuel ratio the engine decides to use on engines after about 2000.
(*some pre 2000 cars as well)

mollwollfumble said:

pommiejohn said:

You’re assuming 100% volumetric efficiency when making your calculation of the volume of air drawn into the engine. A 1.6 litre engine doesn’t necessarily draw in 1.6 litres of air/fuel every 2 revolutions.

Good. I was wondering about that. But could a 1.6 liter engine possibly draw in as little as 0.8 litres in two revolutions? That’s what would be needed to explain the high air-fuel ratio calculated for one of the cars. Wouldn’t that be a huge pressure loss on engine intake?

Volumetric efficiency is a pretty much meaningless parameter at less than full throttle (although it has some bearing on other parameters).

Most vehicles are driven at part throttle most of the time, so draw considerably less air than their swept volume would, on first consideration, indicate.

>>>>>>>Wouldn’t that be a huge pressure loss on engine intake?

Do you mean a huge loss of effective compression ratio (and hence engine efficiency)? If so, yes. Manufacturers overcome this by advancing the ignition slightly on part throttle, so as to extract the greatest possible BMEP (brake mean effective pressure) from the engine.

Consider the drivers, too.

I always achieve much better fuel economy than Mrs V does in her very efficient and economical 1.3 L car. We drive differently.

Michael V said:

Consider the drivers, too.

I always achieve much better fuel economy than Mrs V does in her very efficient and economical 1.3 L car. We drive differently.

I can totally envision Mrs V as a hoon :)

mollwollfumble said:

transition said:

the compression ratios, and stroke and piston diameters for start be helpful

Not needed for the calculation. Neither are wheel diameter, air resistance etc.

Being 4-stroke engines there are always two revolutions per total cylinder volume. So given measured revs per minute at 100 km/hr and known engine volume all of “compression ratios, and stroke and piston diameters” drop out of the calculation. Similarly, given known fuel consumption at 100 km/hr, all the aerodynamic factors drop out of the calculation. Gear ratios, transmission losses and similar also drop out of the calculation. All that can possibly vary is:
1) Measurement errors, which ought to be only of order 10%.
2) Air-fuel ratio.

How about combustion efficiency/exhaust composition and temperature?

Divine Angel said:

Michael V said:

Consider the drivers, too.

I always achieve much better fuel economy than Mrs V does in her very efficient and economical 1.3 L car. We drive differently.

I can totally envision Mrs V as a hoon :)

Yeah, right. :)

She changes the throttle opening much more often than I do, which accounts for the differences in fuel economy.

Michael V said:

Divine Angel said:

Michael V said:

Consider the drivers, too.

I always achieve much better fuel economy than Mrs V does in her very efficient and economical 1.3 L car. We drive differently.

I can totally envision Mrs V as a hoon :)

Yeah, right. :)

She changes the throttle opening much more often than I do, which accounts for the differences in fuel economy.

Mrs V may be the lady who use to pull the choke lever fully out to hang her hand bag on

They shouldn’t install a handbag holder if they didn’t want us to use it.

Divine Angel said:

They shouldn’t install a handbag holder if they didn’t want us to use it.

Tell me about it sister

the “volt” engine is held at its most efficient rpm rather than be accelerated and decelerated all the time

I think that’s when an ICE is most productive – when its rpm is set within the right range for the engine, no doubt they did testing to discover which rpm was the sweet spot that took account for engine wear

it wouldn’t surprise me if the rpm might change over time to take into account engine wear

in company vehicles fuel efficiency does not concern me though anything over say120kmph quickly starts to eat fuel

I used to have an old Vauxhall viva, it was quite thirsty and became thirstier as the cam that worked the points wore away

wookiemeister said:

I used to have an old Vauxhall viva, it was quite thirsty and became thirstier as the cam that worked the points wore away

the dizzy cam simply opened the points.

Adjust point gap

how would the dizzy cam wear in the first place?

Divine Angel said:

Michael V said:

Consider the drivers, too.

I always achieve much better fuel economy than Mrs V does in her very efficient and economical 1.3 L car. We drive differently.

I can totally envision Mrs V as a hoon :)

:D with the funny comments out the window.

The_observer said:

wookiemeister said:

I used to have an old Vauxhall viva, it was quite thirsty and became thirstier as the cam that worked the points wore away

the dizzy cam simply opened the points.

Adjust point gap

how would the dizzy cam wear in the first place?

the cam was so worn that the points could no longer be adjusted

I sold it on to someone else before I went overseas

wookiemeister said:

The_observer said:

wookiemeister said:

I used to have an old Vauxhall viva, it was quite thirsty and became thirstier as the cam that worked the points wore away

the dizzy cam simply opened the points.

Adjust point gap

how would the dizzy cam wear in the first place?

the cam was so worn that the points could no longer be adjusted

I sold it on to someone else before I went overseas

you could have just bought a replacement dizzy from the wreckers

wookiemeister said:

The_observer said:

wookiemeister said:

I used to have an old Vauxhall viva, it was quite thirsty and became thirstier as the cam that worked the points wore away

the dizzy cam simply opened the points.

Adjust point gap

how would the dizzy cam wear in the first place?

the cam was so worn that the points could no longer be adjusted

I sold it on to someone else before I went overseas

What an unusual occurrence. Points heal was made of a wearing plastic, cam was case-hardened steel. Maybe the guy in the factory that day forgot to case-harden the cam. Perhaps one of the points heals in the life of the car had been contaminated with silica or some other hard abrasive. Unusual, most unusual.

>the cam was so worn that the points could no longer be adjusted

probably the shaft bushing.

Unusual, most unusual.

===========

Not in Wookieworld

The_observer said:

wookiemeister said:

The_observer said:

the dizzy cam simply opened the points.

Adjust point gap

how would the dizzy cam wear in the first place?

the cam was so worn that the points could no longer be adjusted

I sold it on to someone else before I went overseas

you could have just bought a replacement dizzy from the wreckers

couldn’t be arsed

>Being 4-stroke engines there are always two revolutions per total cylinder volume. So given measured revs per minute at 100 km/hr and known engine volume all of “compression ratios, and stroke and piston diameters” drop out of the calculation.

doubtful, such things influence the torque/power/efficiency curves.

Michael V said:

wookiemeister said:

The_observer said:

the dizzy cam simply opened the points.

Adjust point gap

how would the dizzy cam wear in the first place?

the cam was so worn that the points could no longer be adjusted

I sold it on to someone else before I went overseas

What an unusual occurrence. Points heal was made of a wearing plastic, cam was case-hardened steel. Maybe the guy in the factory that day forgot to case-harden the cam. Perhaps one of the points heals in the life of the car had been contaminated with silica or some other hard abrasive. Unusual, most unusual.

yeah my step father looked at it and thought it was bloody unusual too

I was going over seas so it was easier to just get rid of it

the viva was never an economical car, the body work was quite thick

wookiemeister said:

The_observer said:

wookiemeister said:

the cam was so worn that the points could no longer be adjusted

I sold it on to someone else before I went overseas

you could have just bought a replacement dizzy from the wreckers

couldn’t be arsed

crickey, what do you do when you get a flat tyre,,, go buy a new car?

jjjust moi said:

Unusual, most unusual.

===========

Not in Wookieworld

come for a holiday in wookieworld

The_observer said:

wookiemeister said:

The_observer said:

you could have just bought a replacement dizzy from the wreckers

couldn’t be arsed

crickey, what do you do when you get a flat tyre,,, go buy a new car?

I normally make sure the tyres are in good condition

the last flat I had was when my former crazy neighbour had suffered a flat and then decided to fuck my tyre as punishment for her bad luck

she used to breed these maine coon cats

we celebrated the day she left. according to someone we knew who lived with her that her old profession was a prositute

wookiemeister said:

jjjust moi said:

Unusual, most unusual.

===========

Not in Wookieworld

come for a holiday in wookieworld

spoiler

the robots go insane and try to kill all the humans