Is DI always more fuel efficient?

[redhat]

My main topic of discussion is -- does direct injection always net the "end-user" better fuel economy?

Let's take two engines, both 5.3. One is a Direct Injected Gen V 5.3 and the other is a regular port-fuel injected Gen IV 5.3. Both equipped with Variable Valve Timing. The DI motor has higher compression.

I know in terms of performance, that is a no brainer... but how's about fuel economy considering everything else is the same.

I am in the beginning stages of a new project and at a choosing which path I am going down. I am trying to decide if the DI engine could net better MPG.

 

[SC Maintenance]

If you follow the newest data from Toyota (who actually got a lot of it from Ford when they swapped data on GDI / Hybrid tech) - you will find that GDI has a sweet spot depending on the injector size.

So this is why you see Toyota and the newer Ford's - among others - running GDI + MPI.

At idle, MPI. Its more efficient, and also helps with intake valve cleaning.

Mid range - GDI only. There sized to be most efficient in this zone.

WOT - they can turn both on. This is because to optimize the GDI injectors, there undersized for WOT situations.

So GDI only is going to have to give up something because it can't be sized properly for every range. I think this is actually why you see things like dilution with a lot of GDI only engines - the injectors are to big to be efficient at idle. Especially on turbo GDI.

Not sure if this answers your question?

 

[GMBoy]

I actually don't think there is any real world difference between GDI and regular FI. I own both styles and even if I could claim additional fuel mileage it just is not worth all the trouble they bring. I will take simple and reliable of complex and troublesome even if there was a 5+ mpg difference. You will end up paying back those fuel savings in valve cleanings and timing chains etc.

 

[redhat]

If you follow the newest data from Toyota (who actually got a lot of it from Ford when they swapped data on GDI / Hybrid tech) - you will find that GDI has a sweet spot depending on the injector size.

So this is why you see Toyota and the newer Ford's - among others - running GDI + MPI.

At idle, MPI. Its more efficient, and also helps with intake valve cleaning.

Mid range - GDI only. There sized to be most efficient in this zone.

WOT - they can turn both on. This is because to optimize the GDI injectors, there undersized for WOT situations.

So GDI only is going to have to give up something because it can't be sized properly for every range. I think this is actually why you see things like dilution with a lot of GDI only engines - the injectors are to big to be efficient at idle. Especially on turbo GDI.

Not sure if this answers your question?

This is helpful, thank you

 

[redhat]

I actually don't think there is any real world difference between GDI and regular FI. I own both styles and even if I could claim additional fuel mileage it just is not worth all the trouble they bring. I will take simple and reliable of complex and troublesome even if there was a 5+ mpg difference. You will end up paying back those fuel savings in valve cleanings and timing chains etc.

If 5+mpg were on the table that would be enough for me to go that way. GM LTx are usually decent with their intake valves and chains. Especially if someone ran a catch can on the PCV side.

But if the difference is nominal and not even able to be seen, then yes I agree PFI + simplicity would be my choice as well.

 

[redhat]

I guess here's another question.

Does the MPG help come more from VVT implementation versus DI over port-fuel? Is the DI more so for emissions?

 

[Rmay635703]

I actually don't think there is any real world difference between GDI and regular FI. I own both styles and even if I could claim additional fuel mileage it just is not worth all the trouble they bring. I will take simple and reliable of complex and troublesome even if there was a 5+ mpg difference. You will end up paying back those fuel savings in valve cleanings and timing chains etc.

The primary advantage of GDI would be to run extremely lean at extremely high compression like a diesel,
functionally lean burn is illegal so GDI is mainly to support higher compression with lower emissions though the jury is out on whether more soot and VOC is actually worth lower nox at higher compression.

 

[bonjo]

GDI adds additional comlexity to the fuel system such as high pressure pump
Can develop LSPI
Cleaning the inlet valve from deposits is more involved
In europe the reapperance of GDI has been since manufacturers switched to small size turbo engines to replace their diesel ones

 

[4WD]

But can some of the GDI shortfalls be aided by the newer transmissions? Whilst our 2017 5.3L is good driving unit with a similar GDI engine - our 2022, mated to the 10 speed is a smoother power train - and gets a couple MPG better …
There is the DFM that’s different - but the slow RPM at highway speed matters as well …

 

[Jetronic]

If you follow the newest data from Toyota (who actually got a lot of it from Ford when they swapped data on GDI / Hybrid tech) - you will find that GDI has a sweet spot depending on the injector size.

So this is why you see Toyota and the newer Ford's - among others - running GDI + MPI.

At idle, MPI. Its more efficient, and also helps with intake valve cleaning.

Mid range - GDI only. There sized to be most efficient in this zone.

WOT - they can turn both on. This is because to optimize the GDI injectors, there undersized for WOT situations.

So GDI only is going to have to give up something because it can't be sized properly for every range. I think this is actually why you see things like dilution with a lot of GDI only engines - the injectors are to big to be efficient at idle. Especially on turbo GDI.

Not sure if this answers your question?

Mitsubishi went with always port injected, and GDI used when needed.

 

[JTK]

In terms of fuel economy and power/performance, I noticed zero difference between my port injected 2016 model year VQ35DE and 2019 model year GDI VQ35DD. Same engine. Different fuel management.

I get it though. GDI allows for more horsepower in a smaller package. It's also makes emissions management easier, which I believe is the reason for it these days.

 

[barryh]

My own port injected C class Mercedes had slightly better official fuel economy than the first iteration of the same engine with direct injection although later versions did boast better figures. What they achieved in reality is another matter but I doubt they could have improved much on mine.

There was one other difference which shouldn't be a surprise. The direct Injection version was noticeably nosier and that's a backward step for the newer car.

In the end direct injection was about emissions and brings no worthwhile benefit to the car owner, only more complexity and potential problems and expense.

 

[demarpaint]

In the end direct injection was about emissions and brings no worthwhile benefit to the car owner, only more complexity and potential problems and expense.

+1

 

[Vercingetorix]

The fastest cars at LeMans all use direct injection, at least everyone I could find info on. Not positive about Cadillac. Toyota, Porsche, Peugeot, Ferrari and BMW, all direct injection. Pretty sure all F1 teams as well. Don’t think any of these have to pass any emissions tests.

 

[pbm]

If you follow the newest data from Toyota (who actually got a lot of it from Ford when they swapped data on GDI / Hybrid tech) - you will find that GDI has a sweet spot depending on the injector size.

So this is why you see Toyota and the newer Ford's - among others - running GDI + MPI.

At idle, MPI. Its more efficient, and also helps with intake valve cleaning.

Mid range - GDI only. There sized to be most efficient in this zone.

WOT - they can turn both on. This is because to optimize the GDI injectors, there undersized for WOT situations.

So GDI only is going to have to give up something because it can't be sized properly for every range. I think this is actually why you see things like dilution with a lot of GDI only engines - the injectors are to big to be efficient at idle. Especially on turbo GDI.

Not sure if this answers your question?

That's an excellent explanation that I didn't know.

While it would add to the cost of a new vehicle it seems worth it to implement the dual GDI/MPI technology on all new vehicles going forward. On a side note....I am impressed with Ford's technical research on this and in other areas (they were the first 'domestic' brand to go the 5w20 route and also did studies on extending OCIs etc....) but, unfortunately, that research doesn't always lead to superior engineering (as witnessed by the disastrous DCT in the Focus/Fiesta that were otherwise very good cars).

 

[Trav]

Mitsubishi went with always port injected, and GDI used when needed.

Mitsubishi was the first production car with DI in 96/97. Many companies used the Mitsubishi GDI system under license.

 

[BMWTurboDzl]

My main topic of discussion is -- does direct injection always net the "end-user" better fuel economy?

Let's take two engines, both 5.3. One is a Direct Injected Gen V 5.3 and the other is a regular port-fuel injected Gen IV 5.3. Both equipped with Variable Valve Timing. The DI motor has higher compression.

I know in terms of performance, that is a no brainer... but how's about fuel economy considering everything else is the same.

I am in the beginning stages of a new project and at a choosing which path I am going down. I am trying to decide if the DI engine could net better MPG.

Power + Fuel Economy. They go together. DI allows for precise metering of fuel and wide tuning ability depending on the PSI of the system along with the number of pulses/sec that the injectors can perform.

VVT helps with low range torque and emissions.

The issues most people worry about with DI are overblown and largely the result of old technology and/or poor tuning from specific automakers. They're also not speaking from experience but second/third/fourth hand information.

Now what has happened is that with ever tighter emissions standards you're seeing these dual MPI-DI systems because DI is a littler dirtier at start up and low rpm. Europe has added OPF (Otto Particulate Filters) which is basically a DPF for gasoline on top of this.

 

[BMWTurboDzl]

Mitsubishi was the first production car with DI in 96/97. Many companies used the Mitsubishi GDI system under license.

Not the Mercedes Gulwing from 1950s?

 

[dfarr67]

When I was shopping around in 2015, I found power and economy was comparable between the two, it came down to other features and the manufacturer. My impression was it allowed higher compression which allows higher efficiency and emissions.

 

[Trav]

Not the Mercedes Gulwing from 1950s?

That was a Bosch mechanical Di system similar to the ones used on WW2 aircraft and diesels for many decades long before MB put it on a gasoline engine. I guess technically neither were the first as some went back to the early 1900's but Mitsubishi was the first to use what we know as Di with electrically fired injectors and an ecm in a mass produced car.