Aye, switch to the low boost map, it will instantly do 50 mpg by my calculations, especially if you drive carefully downhill with the wind behind you!
If it was that simple then all cars would be mapped with amazing economy off boost and as powerful and uneconomic as they need to be in boost. You don't need two boost maps for that! Any decent tuner can map both economy and power into the same map! That's what the throttle and load sensors are for. If you don't understand that then you don't understand efi and basic tuning principles.

 

Quite agree, I think for those that do understand, we already know how this test is going to pan out, but il never understand why people buy an Impreza then go to the bother of trying to increase mpg or in fact find out what's the best mpg they can achieve it just doesn't make sense.
Theres a reason why cars run in closed loop and target stoich =fuel economy

 

Fair comments,I personally am just at the beginning of learning remapping.
I would of thought a high boost aggressive map where say target boost is set to come in earlier,higher boost at less throttle % would use more fuel that a low boost map where target boost is lower and comes in later and only at wot? Of corse this is all open loop yeh.
If we're on open loop say 5% of the time would the low boost map produce better mpg?

What if closed loop was switched off,the car wouldn't keep trying to target 14.7 my low cruise and idle set to 15.2,that's 4% leaner,would this not increase mpg?

I'm not arsed about getting good mpg,if I was I wouldn't be running a big BHP classic as a daily drive,I just find all this very interesting,,,,so I await Lunchmoneys results

 

I don't see anything wrong with owning an Impreza and wanting to get reasonable MPG some of us own them for other reasons as well as the performance.

I happen to like the AWD aspect as well as the size and practicality of the wagon, and the fact it's not a big wallowey (is that a word) 4x4 my only other real choice is a quattro Audi estate, which are more expensive to buy and run, they also do nothing for me, where as I like the presence and look of an Impreza as well as it not being too big and having a reasonable amount of performance in standard guise, well PPP in my instance.

I'm not interested in modding and just want something relatively cheap to buy ie sub £5k easy and cheap to maintain with a bit of go and 4x4, not really much out there that fits the bill.

28mpg around town and 36mpg on a long run, then when I fancy a bit of fun I can throw it down a country road and not worry that I only get 15mpg for 10 mins.

 

Have you considered the leaner you make it the less power you make and so the more throttle angle you require to maintain the same speed? there is a sweet spot,subaru have done a pretty good job.

Boost targets set lower wont really make a lot of difference as you cant ever run less than the pre set WG pressure (circa .7 bar?).
the only real difference you can make, and my car is mapped thus, is increasing the closed loop threshold, my car still targets closed loop 14.7 well into boost (.3 bar) this way whilst labouring the car a little off boost (but still making some possetive pressure, as they do) you are still targeting 14.7 and not horsing in the fuel. But saying that its still only 13.5:1 open loop upto .7 bar for lean spoolup.
the most economic way to drive is off boost and with smooth throttle transitions, have you considered the amount of fuel wasted with unnecessarily sharp openings of the throttle (accel enrichment tossing loads of fuel in here).
Cold starts and temperature also have a massive effect, my car returns better economy whilst being garaged in the winter as its starting from a warmer temp.

 

I couldn't agree more, and TBH i find the impreza very good on fuel for what it is, 25-27mpg on my short 14 mile each way commute is excellent, 30+ on a run too, who can complain? driving style has a lot to do with it.

 

That isn't how the boost control works. You divert the pneumatic signal from the WG actuator via the boost solenoid so you can run lower than actuator pressure.

Running stoich up to 0.3bar isn't a great idea either as you will have to pull ignition to prevent the onset of knock. Running as close as you can to MBT will net the best efficiency and therefore economy and is a better route to follow than running very lean on boost.

 

Im fairly confident I know how the boost control works, and you cannot physically run LESS boost than the pre set actuator pressure. Perhaps you can explain how that is possible? My car runs a controlled 1.6 bar, but the actuator pressure is .9 bar. I CANNOT run less than .9 bar, regardless of the boost control settings...

Im sure my mapper knows what he is doing when running stoich at that boost level on light load, of course it goes richer at that boost level if you increase the load (ie difference between .3 bar half throttle and .3 bar full throttle.)

Car was mapped by Andy Forrest

 

So it will make some difference? If yes then the low boost mpg test is valid and should yield better mpg.

 

Three port or Two port BCS? Normally (two port) you "bleed" (not divert) air off the compressor-actuator line to increase bost pressure. If not bleeding any air at all then you can only run the pre set base boost level, not less.
Three port is slightly different in that you intercept the line pressure and can choose to send it to the actuator or not (so the actuator can see between 0-full boost) this helps with wastegate creep both during spoolup and up the revs where a conventional two port cannot full isolate the actuator and it will see some pressure, and may open slightly allowing for a slower spool or a drop in boost up the revs.
Or am I wrong

 

Not on an economical run. Have you considered the points I have made in the above post? accel, cold, afr?

 

Yes I have considered all your points,I was just quoting you when you say it won't make a lot of difference,which must mean it will make some difference Which is why the op started the thread.
I don't know how much the op is driving on boost as I'm sure you don't either?
But I'm guessing a low boost map will return better mpg than a high boost map.

 

Not another one of these pointless threads. If your that worried about Petrol, then either buy a second car diesel or LPG and job done. My gone thread has more point to it than this

 

definelty. Who does an economy test flat out though? less power-less energy-less fuel. thats physics.

 

I don't think the op is 'Worried' about fuel,he's just doing an interesting test.

Where did the op say he was doing a flat out test?
All he is doing is driving as he always does but with a low boost map.
Or am I missing the point here? If so I'll get mi coat!

 

The test is not accurate then.
Ill take my knowledge away with me.

 

True,It's never going to be accurate and as has been said,the right foot is the best way to control mpg.
Forums and threads wouldn't be much use without discussion and different views,in my eyes it all helps to have a different angle on things as it helps to see all the sides of the story.
Keep your knowledge here and please keep giving as it's always welcome and appreciated

 

Quote:

Originally Posted by ossett2k2

I don't think the op is 'Worried' about fuel,he's just doing an interesting test.

I’m not worried.

Quote:

Originally Posted by ossett2k2

Where did the op say he was doing a flat out test?

Exactly. Just driving as I always do.

Quote:

Originally Posted by boosted

The test is not accurate then.

I am fully aware.

 

After just short of 500 miles (two tanks of fuel) I filled up last night and took readings.

The MPG was surprising.

The previous 500 (approx) miles returned 22.84 MPG.
The 500 (approx) miles on low boost returned 20.25 MPG.

So this, not very, scientific experiment shows high boost is better for MPG

I suspect this may be due to my foot being on the throttle a just a few moments longer to achieve the same speeds.

What ever the cause, it was interesting to do (and read everyone's responses) but I will be staying on high boost as it's more fun and gets better MPG in my car

 

Cool
High Boooooost FTW!!!
I would take it to the mapper and get the boost increased,a Mega boost map might return even better MPG

 

Interesting....... ***** out map it is then