why are our cars so bad on gas?
engineering facts state that the pistons oppose each other therefore creating thrusting opposing forces, the conventional layout is more of a rotary inline motion using less resisting forces, this is the reason a rotary turbo diesel engine developed many years ago was shelved by ford as it was far to economical it was said at the time in 3 cylinder 900cc form in a mk3 escort it would return approx 90mpg, i cant be bothered to look it up but remember reading it in a engineering magazine while at college many years ago 
a bit like the evo which is basically the same car as the sti impreza but with an inline engine,this has just as bad mpg due to similar reasons
no i agree it may not be quite as economical as an inline, what i meant is the poor mpg is mostly down to the turbo and 4wd systems rather than the engine design.
a bit like the evo which is basically the same car as the sti impreza but with an inline engine,this has just as bad mpg due to similar reasons
a bit like the evo which is basically the same car as the sti impreza but with an inline engine,this has just as bad mpg due to similar reasons
Scooby Regular
Joined: Apr 2013
Posts: 4,224
Likes: 0
From: Berks
engineering facts state that the pistons oppose each other therefore creating thrusting opposing forces, the conventional layout is more of a rotary inline motion using less resisting forces, this is the reason a rotary turbo diesel engine developed many years ago was shelved by ford as it was far to economical it was said at the time in 3 cylinder 900cc form in a mk3 escort it would return approx 90mpg, i cant be bothered to look it up but remember reading it in a engineering magazine while at college many years ago
Joined: Apr 2002
Posts: 38,078
Likes: 310
From: The hell where youth and laughter go
8.0:1 thats the main problem.
Where modern stuff is using 10:1 and higher...even with forced induction competitors are well above 9.5:1
More squish = more efficiency. Back in the day (early 1980's) the most efficient petrol engines ran above 12:1 compression, but the introduction of NOX limits and reduced availability of high octane fuel put an end to that. Its only in the last decade that manufacturers have been able to get an engine to run with that much compression again without emissions or reliability issues.
Then we also have lean-burn, and stratified charge combustion. In lamens that is running a petrol engine too lean, saving fuel in the process. Most of the competition is using this whilst Subaru is still using homogeneous charge combustion or richer. Lean-burn is nothing new...it was pioneered in the 60's and seen in production in the 1970s and 80's. Again NOX emissions limits and poor fuel octane killed it so it disappeared totally in the 1990's. But its now come back in the last decade via direct injection and the massive amount of complexities that come along with it.
So, if you want your Subaru to be "good on gas". Raise the compression, fit direct injection - the current models already have tumble ports, but they must be working (many remove/disable it - you can't do that with a stratified charge engine as it'll misfire), change the combustion chamber shape to create a "pocket" that will concentrate the air/fuel mix by the spark plug (either by recessing the exhaust valve, or by using bowl-shaped pistons - like a diesel). And finally fit a NOx storage cat, NOx sensor, and a larger EGR system to get through current emissions. Only then will you get an engine with the efficiency and emissions friendliness of a Golf R....assuming VW haven't fudged the emissions figures on the R as well
Where modern stuff is using 10:1 and higher...even with forced induction competitors are well above 9.5:1
More squish = more efficiency. Back in the day (early 1980's) the most efficient petrol engines ran above 12:1 compression, but the introduction of NOX limits and reduced availability of high octane fuel put an end to that. Its only in the last decade that manufacturers have been able to get an engine to run with that much compression again without emissions or reliability issues.
Then we also have lean-burn, and stratified charge combustion. In lamens that is running a petrol engine too lean, saving fuel in the process. Most of the competition is using this whilst Subaru is still using homogeneous charge combustion or richer. Lean-burn is nothing new...it was pioneered in the 60's and seen in production in the 1970s and 80's. Again NOX emissions limits and poor fuel octane killed it so it disappeared totally in the 1990's. But its now come back in the last decade via direct injection and the massive amount of complexities that come along with it.
So, if you want your Subaru to be "good on gas". Raise the compression, fit direct injection - the current models already have tumble ports, but they must be working (many remove/disable it - you can't do that with a stratified charge engine as it'll misfire), change the combustion chamber shape to create a "pocket" that will concentrate the air/fuel mix by the spark plug (either by recessing the exhaust valve, or by using bowl-shaped pistons - like a diesel). And finally fit a NOx storage cat, NOx sensor, and a larger EGR system to get through current emissions. Only then will you get an engine with the efficiency and emissions friendliness of a Golf R....assuming VW haven't fudged the emissions figures on the R as well
Last edited by ALi-B; Oct 23, 2015 at 07:13 PM.
Thread Starter
Scooby Regular
Joined: Jun 2014
Posts: 566
Likes: 0
From: england
8.0:1 thats the main problem.
Where modern stuff is using 10:1 and higher...even with forced induction competitors are well above 9.5:1
More squish = more efficiency. Back in the day (early 1980's) the most efficient petrol engines ran above 12:1 compression, but the introduction of NOX limits and reduced availability of high octane fuel put an end to that. Its only in the last decade that manufacturers have been able to get an engine to run with that much compression again without emissions or reliability issues.
Then we also have lean-burn, and stratified charge combustion. In lamens that is running a petrol engine too lean, saving fuel in the process. Most of the competition is using this whilst Subaru is still using homogeneous charge combustion or richer. Lean-burn is nothing new...it was pioneered in the 60's and seen in production in the 1970s and 80's. Again NOX emissions limits and poor fuel octane killed it so it disappeared totally in the 1990's. But its now come back in the last decade via direct injection and the massive amount of complexities that come along with it.
So, if you want your Subaru to be "good on gas". Raise the compression, fit direct injection - the current models already have tumble ports, but they must be working (many remove/disable it - you can't do that with a stratified charge engine as it'll misfire), change the combustion chamber shape to create a "pocket" that will concentrate the air/fuel mix by the spark plug (either by recessing the exhaust valve, or by using bowl-shaped pistons - like a diesel). And finally fit a NOx storage cat, NOx sensor, and a larger EGR system to get through current emissions. Only then will you get an engine with the efficiency and emissions friendliness of a Golf R....assuming VW haven't fudged the emissions figures on the R as well
Where modern stuff is using 10:1 and higher...even with forced induction competitors are well above 9.5:1
More squish = more efficiency. Back in the day (early 1980's) the most efficient petrol engines ran above 12:1 compression, but the introduction of NOX limits and reduced availability of high octane fuel put an end to that. Its only in the last decade that manufacturers have been able to get an engine to run with that much compression again without emissions or reliability issues.
Then we also have lean-burn, and stratified charge combustion. In lamens that is running a petrol engine too lean, saving fuel in the process. Most of the competition is using this whilst Subaru is still using homogeneous charge combustion or richer. Lean-burn is nothing new...it was pioneered in the 60's and seen in production in the 1970s and 80's. Again NOX emissions limits and poor fuel octane killed it so it disappeared totally in the 1990's. But its now come back in the last decade via direct injection and the massive amount of complexities that come along with it.
So, if you want your Subaru to be "good on gas". Raise the compression, fit direct injection - the current models already have tumble ports, but they must be working (many remove/disable it - you can't do that with a stratified charge engine as it'll misfire), change the combustion chamber shape to create a "pocket" that will concentrate the air/fuel mix by the spark plug (either by recessing the exhaust valve, or by using bowl-shaped pistons - like a diesel). And finally fit a NOx storage cat, NOx sensor, and a larger EGR system to get through current emissions. Only then will you get an engine with the efficiency and emissions friendliness of a Golf R....assuming VW haven't fudged the emissions figures on the R as well
I used to get between anywhere between 19-22mpg on the urban cylce. Now I seem to get 15-16.5!!!
I knew there must be a reason for it and hadn't even thought about that, till you mentioned it... 'Cause it would have been fitted at about the same time as I realised that economy had worsened.
In the meantime, I fitted a brand new OEM lambda sensor...HOPING that was the reason...but no it wasn't, annoyingly.
Hmmn, I wonder if that IS the reason..............................
do you actually understand physics or indeed how a car works? By fitting a light weight crank pulley/fly wheel you're lowering inertia in the driveline, hence why revs rise/fall faster. The amount of air/fuel (thus throttle opening) required to maintain a given torque is basically independent of that, so you'll see a minuscule difference if any at all.Any difference would be negligible, one way or another.
Just that there was a 'binary'-like point at which my U/C fuel usage dropped from bad to terrible lol, and I sort of worked out that it could well have coincided at the point when I went from the OEM 11kg f/w to a 7.5kg machined one.
I was just clutching at straws, really.... Desperately trying to find a 'scapegoat' (despite how illogical/unlikely).
Last edited by joz8968; Oct 24, 2015 at 02:43 PM.
Scooby Regular
Joined: Jan 2011
Posts: 315
Likes: 21
With regards to the AWD being largely responsible for poor mpg, if you're on a long boring motorway journey would setting the dccd to maximum rear bias make any negligible improvement to mpg? Or is that wishful thinking?
But its very brave of you Matt to admit that the STi has a lighter flywheel then the WRX, making it lighter and faster!!!
Scooby Regular
iTrader: (3)
Joined: Aug 2000
Posts: 25,565
Likes: 2
From: 1600cc's of twin scroll fun :)
The DCCD deals with torque distribution so setting it to the rear wont do anything, it doesn't deal with the awd itself which contrary to popular belief, stays as it is no matter the setting.
Scooby Regular
Joined: Sep 2008
Posts: 5,314
Likes: 19
From: Wakefield
Not for performance it isn't, rotational mass and all that...or are you referring to 'fuel economy' again in a 2.0l turbocharged petrol car.....which is a pointless discussion as they are not built for that, they are a performance car not an economical one.
Last edited by The Pink Ninja; Nov 13, 2015 at 05:12 PM.
Thread Starter
Scooby Regular
Joined: Jun 2014
Posts: 566
Likes: 0
From: england
Hardly pointless when for the same amount of fuel put in you could own a v8 5l isf. A real performance car with over 400hp to begin with
Strange analogy being the ISF is twice as much to buy and a totally different style of car...Anyone buying an Impreza and then questioning fuel consumption bought the wrong car, I hear VW get 80mpg out of a diesel
Scooby Regular
Joined: Mar 2014
Posts: 121
Likes: 0
From: aberdeen
Interesting topic and funny at times, I agree, if you want or own an Impreza surely mpg is the last thing you should be thinking of. Even the n/a Impreza's are not exactly what you call economical due to the awd I'm only getting 22mpg with the supercharger, when the tanks empty I just fill it up with a smile because it's the car I want to drive I just don't care about mpg.
Scooby Regular
iTrader: (3)
Joined: Aug 2000
Posts: 25,565
Likes: 2
From: 1600cc's of twin scroll fun :)
As are most Scooby owners.
Studies have proved,the bigger the grin the heavier the right foot is.
People who get 40+mpg
Heads over to projects..........
Scooby Regular
Joined: Mar 2014
Posts: 121
Likes: 0
From: aberdeen
Like you say I'm proud to own and drive a scooby and I have got a bit of a lead foot,The project really was finished well over a year ago and it's always been a daily driver since I started the project but like you turbo guys I'm always looking for more power so I keep adding to the thread to let people know how it's going. Just really as an inspiration to the non turbo guys that good power can be had out of what is a good engine.
I've not had it on a dyno but it's quick ( in terms of forced induction n/a) difficult to say what bhp possibly 180 -200 but as you know it's the torque the s/c give you that makes all the difference. All I can go on really is 0-60 and I'm now down in the low 6 seconds, and just keep pulling until, Well you guys know the rest
it's great no lag, so it easily holds it own on the road, il keep pushing it until something goes bang then maybe throw throw in a 3.0 and supercharge that.
I'm proud it sort of 1 of a kind and it's all my own work but more importantly I did in a scooby
The best bit is when the muppets pull up along side you reving away like *****, like you turbo guys I just show them what a scooby's all about,
I haven't got 1 wrx or sti badge anywhere on my car because it simply isn't either it's something completely different, and I **** myself laughing when I see that kinda of thing going on.
(Sorry for the long post)
I've not had it on a dyno but it's quick ( in terms of forced induction n/a) difficult to say what bhp possibly 180 -200 but as you know it's the torque the s/c give you that makes all the difference. All I can go on really is 0-60 and I'm now down in the low 6 seconds, and just keep pulling until, Well you guys know the rest
it's great no lag, so it easily holds it own on the road, il keep pushing it until something goes bang then maybe throw throw in a 3.0 and supercharge that.
I'm proud it sort of 1 of a kind and it's all my own work but more importantly I did in a scooby
The best bit is when the muppets pull up along side you reving away like *****, like you turbo guys I just show them what a scooby's all about,
I haven't got 1 wrx or sti badge anywhere on my car because it simply isn't either it's something completely different, and I **** myself laughing when I see that kinda of thing going on.
(Sorry for the long post)
Last edited by mikeblackett; Nov 14, 2015 at 10:37 AM.
Agree with the last few comments. Honestly, if you're even looking at MPG figures in an Impreza, you may have bought the wrong car. I honestly don't care what MPG I get. If I did, I'd buy boring family diesel. I absolutely love driving my Impreza, which is part due to the fact that MPG figures aren't in the back of my mind. I understand that some people are all about economy, that's fine, and I've been known to try and get some of my previous cars to the highest MPG figure I can get (which has shown me some manufacturers clearly lie......Not mentioning any names *cough* Renault *cough*), but in the Impreza, I honestly don't care.
Joined: Apr 2002
Posts: 38,078
Likes: 310
From: The hell where youth and laughter go
Many good marques have died or been ruined by market forces where owners have complained about poor fuel consumption on a performance car. These type of people should be slapped the on the back of the head and shouted in their ear "fast cars use lots of fuel, what did you f**kin' expect!"
The death knell has been sounded for many V6 and V8 engines as well as supercharging for them to be replaced with boring and 4pots and diesels. The manual gearbox will suffer the same fate as the mainstream sheeple demand auto or DSG.
Last edited by ALi-B; Nov 14, 2015 at 08:11 PM.
