[crabu2]

I hope someone can give me a good answer to this because I'm a bit confused on this....

The way I understand it .... the more air you pump into an engine, the more gas you need.. So a JB+ or the likes should cause a fuel economy reduction.

What gets me is when I hear people say they get better fuel economy with these box tunes when driving normally. How is that possible?

I see that when you're accelerating, you don't need as much throttle because you're making more power, but shouldn't there be a fuel hit even when not hammering on it? And when you're just cruising, and the turbo isn't spooling, wouldn't one be using the same amount of fuel as if there was no box?

Can someone give me some legit reasons/explanations on why I hear so many people say they get better mpgs with a box that increases boost?

Thanks!

[BimmerAg]

The JB+ and other units increase boost but typically leave it to the DME to retard timing when knock is sensed. Since the stock ignition timing is typically set to a conservative value, more advanced ignition timing can improve engine efficiency and fuel economy..

Flash tunes can provide an even greater benefit because they can advance the ignition timing close to the knock threshold where even more efficiency (and power) gains can be had.

[crabu2]

Originally Posted by BimmerAg

The JB+ and other units increase boost but typically leave it to the DME to retard timing when knock is sensed. Since the stock ignition timing is typically set to a conservative value, more advanced ignition timing can improve engine efficiency and fuel economy.

but something like a jb+.. do they increase timing too, or just pump more air in?

[BimmerAg]

Originally Posted by crabu2

but something like a jb+.. do they increase timing too, or just pump more air in?

They usually don't increase timing, but with more boost the stock DME would typically retard timing Since the JB+ doesn't change timing at all, it's effectively advancing it compared to where a stock map might be at the same boost level.

[BEM-S4]

I need to hire a fuel truck as a support vehicle for my cars. Post- Dinan on both of them fuel economy way down.

[The Wind Breezes]

Timing is already advanced for optimal power under low load situations, so that's not a factor. The only way a tune will give you better fuel economy under low load is if you lean out the air fuel ratio. Removing your cat will help a little bit too, and a lot of people do that in combination with a tune. More info on fueling, these cars are probably pretty conservative with regard to "protective fueling" which means richer AFR depending on how hot the DME thinks things are. You wouldn't necessarily have to be under high load to incur that, but I'm not very knowledgeable about the N54 / N55 DMEs so I couldn't say how they're mapped. You can observe for yourself the air fuel readings with a logging program. The upstream o2 sensor is wideband stock.

In my last car I experimented with running slightly north of stoich under low RPM / load. Yes, it will give you better fuel economy, but you NEED an EGT gage to do it safely otherwise you're playing with fire.

One interesting thing about direct injection is you can use a method called stratified combustion which gives a locally stoich combustion that's overall lean with respect to the total air in the cylinder. This gives really good fuel economy under low load but the emissions are "unacceptable" so manufacturers don't do it. The DME is capable of making it happen, but it's not a simple remap to enable this and 99% of people getting a tune care mostly about power, so I don't know any aftermarket tuners who offer that feature.

[crabu2]

So the bottom line is these boxes aren't going to give anyone any better fuel economy... If anything, they'll make it worse because of the fun factor...

[bimmer456]

I would think running lean would improve fuel economy but is "Playing with Fire" as said earlier. The MPPSK has no effect on fuel economy or emissions, just fun factor. Perhaps the JB4 tuners can learn how to do this map to get CARB 50 state certification.

[Vigilante375]

Honestly, I think it comes down to your driving habits and where you drive (city or highway). Unless you're running FBO and max PSI, then I wouldn't think you'd get better MPGs. If its a fairly conservative tune, you might see 1 or 2 MPG gain.

With a canned tune and nothing else, I couldn't see why it would be possible. As long as it's on the "lowest" setting. But again, it's not going to be anything phenomenal.

[crabu2]

Originally Posted by Vigilante375

Honestly, I think it comes down to your driving habits and where you drive (city or highway). Unless you're running FBO and max PSI, then I wouldn't think you'd get better MPGs. If its a fairly conservative tune, you might see 1 or 2 MPG gain.

With a canned tune and nothing else, I couldn't see why it would be possible. As long as it's on the "lowest" setting. But again, it's not going to be anything phenomenal.

how can you get better mpg is the question. because when you increase boost, you're going to increase fueling.

You're saying one might see 1 or 2 mpg increase with a canned tune.. I don't see how that's possible because if your putting your foot into the throttle for more power, which means worse mpg, your basically just running on a stick tune.

[Vigilante375]

Originally Posted by crabu2

how can you get better mpg is the question. because when you increase boost, you're going to increase fueling.

You're saying one might see 1 or 2 mpg increase with a canned tune.. I don't see how that's possible because if your putting your foot into the throttle for more power, which means worse mpg, your basically just running on a stick tune.

Well, think about it this way. You have a base tune from a JB4, give you an extra.....4 PSI plus everything else it changes in the ECU/ECM. If you're light on the throttle, driving normal at highway speed of 60. Then in theory you shouldn't be using that much more fuel or making that much more power since you're just cruising along.

Thats where people probably say they are getting better MPGs. And to throw this in the loop. In my manual 135i that is stock, I see an increase of 4 MPG if I drive around 75 MPH as compared to ~65 MPH. Now why the hell would I see an increase of 4 MPGs when the RPMs are higher? Turbo'd cars just don't make sense sometimes with their fuel economy.

I normally see 24-25 MPGs driving 65 MPH but when the couple of times I've done some 75MPH trips, I see just over 29 MPGs.

[RM7]

Lots of factory tunes run on the rich side to deal with every possible situation and provide adequate cooling to the turbo and engine. You can often "unlock" power and efficiency by leaning out some, but there becomes a fine line where you may start to significantly accelerate wear on engine components in the pursuit of more power. You may not encounter the extreme conditions every day where the factory tune is "protecting" the components, but it's also there for a reason, which means that tuners really need to know what they are doing when they go messing around with this stuff. Sometimes your injectors won't support the flow rates required for more airflow, sometimes the fuel pump will be the weak point, or the fuel rail, cooling in extreme environments and use, etc...

On the flipside, most any time you tune, you will have more boost available earlier, which will mean more fuel is used in acceleration, which will generally mean less mpg. Depending on your driving habits and the engine, this may not be significant though or you may be able to minimize it.

[insanecoder]

I wouldnt put much weight on the mpg after a piggyback
who knows what calcs the DME used to calc the mpg
those calcs assumed correct sensor values which are now suspect with the piggyback

[crabu2]

Originally Posted by insanecoder

I wouldnt put much weight on the mpg after a piggyback
who knows what calcs the DME used to calc the mpg
those calcs assumed correct sensor values which are now suspect with the piggyback

That makes a lot of sense.. but the bottom line is that you can't get better mpg with any piggyback tune because none will remap fueling or bump up timing.. It seems on turboed engines, all they do is increase boost and let the factory tune handle everything else that might be needed for the increase in boost.

Would you agree?

[davis449]

From personal experience, no flash tune has ever resulted in better MPG.

[BimmerAg]

Originally Posted by The Wind Breezes

Timing is already advanced for optimal power under low load situations, so that's not a factor. The only way a tune will give you better fuel economy under low load is if you lean out the air fuel ratio. Removing your cat will help a little bit too, and a lot of people do that in combination with a tune. More info on fueling, these cars are probably pretty conservative with regard to "protective fueling" which means richer AFR depending on how hot the DME thinks things are. You wouldn't necessarily have to be under high load to incur that, but I'm not very knowledgeable about the N54 / N55 DMEs so I couldn't say how they're mapped. You can observe for yourself the air fuel readings with a logging program. The upstream o2 sensor is wideband stock.

In my last car I experimented with running slightly north of stoich under low RPM / load. Yes, it will give you better fuel economy, but you NEED an EGT gage to do it safely otherwise you're playing with fire.

One interesting thing about direct injection is you can use a method called stratified combustion which gives a locally stoich combustion that's overall lean with respect to the total air in the cylinder. This gives really good fuel economy under low load but the emissions are "unacceptable" so manufacturers don't do it. The DME is capable of making it happen, but it's not a simple remap to enable this and 99% of people getting a tune care mostly about power, so I don't know any aftermarket tuners who offer that feature.

Good points. For stratified combustion, the engine-out emissions are actually fairly similar to those of stoichiometric combustion. The problem is that typical 3-way catalysts lose efficiency very quickly at lean AFRs. Basically if manufacturers wanted to run a gasoline engine with stratified combustion, they would need similar emissions equipment as diesel engines have. Mercedes is actually bringing a stratified charge engine to the US that will use a Lean NOx trap to store NOx emissions at light loads. It will then run under stoich operation at high loads and the trap will release the NOx to be taken care of by the 3-way catalyst. This is supposed to result in a 7% improvement in overall fuel economy.
http://www.greencarcongress.com/2014...140207-mb.html

[The Wind Breezes]

Originally Posted by BimmerAg

emissions

Thanks for the additional info, that's interesting.

[insanecoder]

Originally Posted by crabu2

That makes a lot of sense.. but the bottom line is that you can't get better mpg with any piggyback tune because none will remap fueling or bump up timing.. It seems on turboed engines, all they do is increase boost and let the factory tune handle everything else that might be needed for the increase in boost.

Would you agree?

Well there are some what-ifs and I do not know what the end result is because you really need to know how the ECU is responding and I dont do this fulltime
the theory is:
if AFR is going lean you may get better output and thus efficiency but the tradeoff is your engine reliability will be down

in theory if the ECU is doing its job keeping AFR at stoichiometric then alls equal your efficiency should remain the same theoretically but in the real world you will likely experience losses (ie more blow thru and other losses)

I would say the only real way you get higher efficiency via boost is by going lean and thats damaging
but again with piggybacks its hard to know whats going on

[RM7]

Originally Posted by insanecoder

Well there are some what-ifs and I do not know what the end result is because you really need to know how the ECU is responding and I dont do this fulltime
the theory is:
if AFR is going lean you may get better output and thus efficiency but the tradeoff is your engine reliability will be down

in theory if the ECU is doing its job keeping AFR at stoichiometric then alls equal your efficiency should remain the same theoretically but in the real world you will likely experience losses (ie more blow thru and other losses)

I would say the only real way you get higher efficiency via boost is by going lean and thats damaging
but again with piggybacks its hard to know whats going on

ECUs do not keep turbo engines stoiometric under boost.

[Vigilante375]

Honestly, if you're going to boost the power of a vehicle in any shape or form. MPGs shouldn't be a concern.

All I'd want to know is what I'm doing going to put more wear and tear on something else so I can upgrade it at the same time, how much more power I'm going to be making and how reliable will it be plus getting good parts at a reasonable price.

[crabu2]

Originally Posted by Vigilante375

Honestly, if you're going to boost the power of a vehicle in any shape or form. MPGs shouldn't be a concern.

All I'd want to know is what I'm doing going to put more wear and tear on something else so I can upgrade it at the same time, how much more power I'm going to be making and how reliable will it be plus getting good parts at a reasonable price.

that in already know... my question was because I've seen many people say they get better mpg with a tune when driving normally. that didn't make sense.. and the replies here confirm my thinking... performance tunes won't give better mpg, just because you're not on the throttle.

[eluded]

If a tune is reducing back pressure (down pipe, exhaust, larger exhaust piping, etc. ) than in theory you could get better miles per gallon.

However if it's just electronics I doubt anyone could tune the timing and what not to give you slightly better gas mileage that you would notice.