Further to actual MPG discussion on this thread I have filled up last night and switched to other map.
This wont be just a long drive, I will just use the car as normally do over the next week or two and when I fill up again I'll share my results.

At least one other person was interested in the results, not just me


I've already commented on my ECU,
But if anyone has any questions about my car or driving, just ask


Of course I realise this is just one man, one car and one tank of fuel, so it wont be the worlds most conclusive experiment, but it might bring an interesting observation.

 

Hi mate

It was me who was interested in the result

I've been thinking about duel maps for a while as I travel down to London a few times a year plus a fair few other motorway journeys. I am interested to see if this setup could save fuel on a 500 mile trip. It takes about a tank and half(ish) at the moment to get to London and back.

 

Look forward to seeing the results.
Subscribed

 

I hardly notice a difference between maps on mine have a 1 bar map and a 1.6 bar map on syvecs and both still pathetic on fuel so its just kept on the high power map lol

 

I have a feeling that will be my result as well. Time will tell.

 

Closed loop on a wide band made a big difference though but both maps still similar mpg just better off boost

 

I know some mappers just lower the boost target and leave fuel and ignition maps the same on both high and low boost.
A decent mapper will adjust the whole map(the proper way) So if it's done correctly you should see an MPG difference with the low boost map.
The closed loop leaner tune will defiantly see an improvement

 

Thats my thoughts same fuels tables but lower boost target, the lazy way to map, 850cc injectors though so probaly hard to get lower mpg, it dont bother me though but would feel the use out the weeker powered map if i got mpg gains.

 

When you start going for big power like you jay then MPG is the last thing on your mind I suppose.
Plenty of lazy mappers out there,but plenty of real good professional mappers too,just making sure you find one of the good ones

@lunchmoney,,are you going for a map on the rollers or a road map?
See if the mapper will show you the difference between the high and low boost maps,even get a pic or two of the boost,fuel,ignition,maf scale,injector scale,tables ect...
And see if he will let you have a peek at the datalog files too

 

+1
Been thinking about doing this myself!
Interested in results

 

The mapping was done a few years ago on road, so nothing new is getting done now. I've just never used the low boost one until now.

 

Wheels also DO make a difference. Big wide wheels with sticky semi slick tyres have alot of rolling resistance. I woukd expect to see a marked improvment with standard 17s on road tyres on a 500mile journey

 

Cool 😎
Be nice to see the test results.

 

Mine seems alot better on low boost. Be good see your results

 

In theory it shouldn't make a difference! mapped right to stoich should just mean that a higher boost map should be capable of giving more when your right foot asks for it, when the right foot isn't asking for it it should behave the same!

The only way to save fuel with a different cal would be to pull fuelling out, in which case you'll run leaner, run hotter, lose efficiency, risk det.

There might be a compromise to find? there might be a way to input exhaust temps into a motorway specific map which leans it off to a safe upper EGT limit? Theres some pretty advanced mapping requirements going on here though and if your venturing into lean then your risking venturing into det.

Im no expert, but I was origionally sold on the idea of having switchable maps to get a frugal map, but on investigation there didn't seem to be any replacement for a lighter right foot.

Interested to see if your findings differ though.

 

That is true.

So in the spirit of getting all the data together for this ad-hoc "experiment" here is some info about my car (none of which is going to change, the only item changed is the hi/low boost):
MY98 JDM STI;
Aftermarket ECU (I forget which);
3in decat exhaust
Undertray heat shield has been removed as it was falling to bits anyway;
18 in wheels with 215/35 tyres (good wet grip, cant recall exact brand), only about 3000 miles old;
No further mods.
Daily drive to work in traffic, no "spirited" driving
Occasional long journey.

 

Yes, I know. But I like to experiment

 

I've mapped mine so I can hit full boost at half throttle,boost comes in earlier so engine loads Higher at lower rpm(high boost map) I've had to add fuel and pull some timing on this.
So if mapping a low boost(economy map) in theory I should be able to lean the map back again. I'm definitely no expert but I would have thought if mapped correctly then a low boost map will save you fuel?

 

Wasn't knocking your efforts, just wanted to highlight your dabbling with det and ej's really don't like that.

 

Does AVCS increase MPG circa 10% on an Impreza?

 

This will be interesting to see. I put quite a few miles on my car taking in all types of raods and traffic conditions. I have four maps (0.5, 1.0, 1.3 and 1.4). I always run 1.4 so next time I fill up, I'm gonna swap to the 0.5 and see if there's a dfference.

Another test can't harm this thread...

 

If the off boost area on all maps is the same, unless altered specifically by the mapper, then it will return the same mpg when kept off boost.

I tried running 15.5 afr on my last 98 wrx and on a controlled run to work and back during the week (10 x 22 mile trips) it made maybe 1 mpg difference versus the previous week at 14.7. Both weeks were pretty much same conditions and driving style.

Not really worth it imho.

 

Forgot to say 14.7 returned 25mpg and 15.5 returned 26mpg. Problem is that it isn't the most accurate of testing.

 

Well it is worth it as there is more than one person interested in the results.
We are all fully aware it wont be 100% accurate as it is just me and my car. To test it completely we'd need 10000 identical cars, 10000 identical drivers and 10000 identical driving conditions. Then we could start. However as that cant happen I am doing it on my own. It makes no difference to you what map I drive in and how long I drive it for. I'm doing it anyway and will share my results once I've gone through a couple of tanks of fuel.

As an update I've been on holiday and the car has only done about 100 miles since switching, so I dont have any numbers yet.

 

Ok, excuse me for offering "my" findings and opinion.

 

what you have done is a far better idea than running a high boost and low boost map as comparison, after all we spend 99% of our time off boost in a closed loop cruise situation. I think 1 mpg is a good average improvement by leaning off the cruise mix.
Changing from hi to low boost maps isnt going to make any difference at all if your on an economy cruise off boost is it?

 

exactly!

I was trying to help by stating that the cruis area of any map will indeed be closed loop and therefore nothing to do with boost profiles, but what would I know.

 

Have you read all of the thread? We know! I am doing to assuage my own curiosity and have offered to share my results. To you guys saying there is no point in doing it, thanks for sharing your experience, hopefully I'll get the same results.

 

Can you confirm that you actually know that the off boost areas of your maps are actually different? If they are the same then there is no point doing any tests. If they are different then yes, its worth testing.

I'm not arguing with you, just trying at add information to the discussion. If you are running lean enough to increase mpg significantly it can have an adverse effect on engine components due to raised egt's.

 

Read post #7
I think Lunchmoney is trying to say if you read the whole thread then you would realize he already knows about the closed loop.
So "if" a decent mapper was used then the low boost map won't just be less boost.

HTH