# Gas Direct Injection - what are the pitfalls for airplane conversions?

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#### Nims11

##### Well-Known Member
With GDI using highly compressed fuel, it seems likely that this would prevent its use at higher altitudes. But I'm not sure about this, perhaps the common rail system and injectors are built strong enough to be stable even at higher altitudes. Does anyone have knowledge about this?

The reason I ask is because some auto makers are starting to produce turbocharged, light weight, powerful GDI engines that, on paper anyway, seem to have great potential for airplane conversions.

#### Himat

##### Well-Known Member
With GDI using highly compressed fuel, it seems likely that this would prevent its use at higher altitudes.
Why should it be any problem?
The difference in altitude pressure is probably only a fraction of the fuel pressure.

#### Jay Kempf

##### Curmudgeon in Training (CIT)
With GDI using highly compressed fuel, it seems likely that this would prevent its use at higher altitudes. But I'm not sure about this, perhaps the common rail system and injectors are built strong enough to be stable even at higher altitudes. Does anyone have knowledge about this?

The reason I ask is because some auto makers are starting to produce turbocharged, light weight, powerful GDI engines that, on paper anyway, seem to have great potential for airplane conversions.
Direct injection is one of the largest improvement in combustion efficiency to come along in a long while. It pretty much is superior in all ways except slight complexity issues and a few failure modes that were tested to death than all things that came before it. No problems at altitude like any other electronic fuel injection system. It still uses MAF and/or MAP like any other system and the injection pressure is way above cylinder pressure contained and so it isn't going to be affected by atmospheric changes.

#### BoKu

##### Pundit
HBA Supporter
...perhaps the common rail system and injectors are built strong enough to be stable even at higher altitudes...
The atmospheric pressure difference between sea level and outer space is less than 15 PSI.

Thanks, Bob K.

#### TFF

##### Well-Known Member
Direct injection is hard to make without a lot of technology. Fine machining, materials that dont coke or melt, control, very high operating pressures. It is great if you can use someone else's parts in your own stuff, but to whittle something out in the back yard is not going to happen.

#### ekimneirbo

##### Banned
I think the new direct injection engines use a very high pressure pump that is engine driven.....so I don't know of any way to have a backup pump.
Also, if I remember correctly, most of these engines are operated at high compression ratios which could be a potential problem. I assume these engines have been tested to reasonable altitudes since someone may drive up Pikes Peak someday, but wonder how they might operate if taken to
even higher altitudes with thinner air.

#### rv6ejguy

##### Well-Known Member
GDI injection strategies are closer to diesel than SI port injection EFI. Without an OEM solution, you are looking at aftermarket ECUs such as Bosch Motorsport or Specialist Components- both very expensive. Without a lot of knowledge about system programming, engines and a dyno, you have little hope of making this work IMO.

As we discussed by PM, most modern OEM ECUs are so intertwined with chassis sensors, security/ key interlocks etc., your chances of making it run outside the original car without all the sensors and OEM wiring intact are minimal. You'll have a no start condition or a dozen codes thrown leading to running issues/ limp mode intervention.

#### rv6ejguy

##### Well-Known Member
I think the new direct injection engines use a very high pressure pump that is engine driven.....so I don't know of any way to have a backup pump.
Also, if I remember correctly, most of these engines are operated at high compression ratios which could be a potential problem. I assume these engines have been tested to reasonable altitudes since someone may drive up Pikes Peak someday, but wonder how they might operate if taken to
even higher altitudes with thinner air.
Most OEMs are using MAF and baro compensation in the solution so no problem at any reasonable altitudes people would be flying at without O2. That won't be the problem. The problem will be to get it to even run in the first place with many missing chassis sensor inputs I think.

#### Himat

##### Well-Known Member
As we discussed by PM, most modern OEM ECUs are so intertwined with chassis sensors, security/ key interlocks etc., your chances of making it run outside the original car without all the sensors and OEM wiring intact are minimal. You'll have a no start condition or a dozen codes thrown leading to running issues/ limp mode intervention.
There is one option that is not easily executed.
Reverse engineer or by other means get to know the ECU program code. With this information it should be possible to reassemble a new ECU code that only contain the engine relevant program. I did read someone that did this with a Land Rover TD5 ECU, if this is possible with more recent car ECU's without inside information I don't know.

#### pictsidhe

##### Well-Known Member
Altitude won't hurt it all, unless you get done to the lower flow limit of the fuel injectors, but unless you try idling at 60,000 feet, that's not going to be an issue anyway. If you're idling at 60,000 feet, you're probably worrying about other things than your engine idling badly... If you run an oem setup on a dyno and read the injection and ignition timing map, you could use an aftermarket ecu in case of seatbelt sensors or other such silliness. Injection pressures are in the diesel range, but plenty of people mess with those systems.

#### rv6ejguy

##### Well-Known Member
There is one option that is not easily executed.
Reverse engineer or by other means get to know the ECU program code. With this information it should be possible to reassemble a new ECU code that only contain the engine relevant program. I did read someone that did this with a Land Rover TD5 ECU, if this is possible with more recent car ECU's without inside information I don't know.
This has been done with GM ECUs in the past on various conversions, not always with successful conclusions. I can think of two crashes and one engine meltdown showing its not always easy to comprehend all the interrelations of code.

I think many people don't appreciate how sophisticated modern ECUs have become, years ago some had MILLIONS of lines of code. Good luck with deciphering all that, trimming the fat, reassembling and revalidating the code without some inside information. Most OEMs are not going to help either. In fact, some OEMs now have individual PIN codes just to access memory on a certain ECU. Another protection strategy is to erase memory if someone tries to access it without the proper code.

Of course anything can be hacked with the right talent and time spent. You need to find the right guy though. You could scope fuel and ignition inputs and data log it all on a dyno to see what they are doing, then possibly duplicate that with an aftermarket ECU however I don't see the point in using a $6k ECU on a$1500 junkyard GDI engine and going to all that trouble. Using an existing, proven port EFI engine would be hours and dollars ahead IMO.

#### akwrencher

##### Well-Known Member
HBA Supporter
Ross, you are probably one hundred percent correct. However, my crystal ball see's a new project in your ECU future in a couple years...:gig:

#### rv7charlie

##### Well-Known Member
If the goal is a high-HP setup, the likely solution is a manufacturer's 'street rod' crate engine & controller, that doesn't need all the chassis/trans sensors. GM sells controllers at a very reasonable price for the LS motors right now. It seems highly likely that they will do the same for the DI Corvette engine in the near future (if it's not available already).

Might be a bit tougher to find something like that for a low (<200 HP) engine, though.

Charlie

#### rv6ejguy

##### Well-Known Member
Ross, you are probably one hundred percent correct. However, my crystal ball see's a new project in your ECU future in a couple years...:gig:
We've been approached by a couple of engine vendors to work on that and it may be something we do in the future if the demand warrants it. Right now the big markets for us in aviation are equipping legacy carbed engines with port injection. There are thousands out there and that will continue to keep us busy for a long time to come. Seeing a lot of demand for Lycoming stuff and to a lesser extent Rotax. Hundreds of Subarus are flying with our stuff to- replacing the OEM EFI system.

#### proppastie

##### Well-Known Member
Log Member
A friends son, was putting different chips in a modern VW, I thought these chips can be purchased in Hot Rod mags. Some as I understand it are programmable. Not my field, but you might find help at the local race track. My only suggestion is to use a proven docile airframe to test at altitude. (C-150, C-172 PA 28, etc). Engine/product development is "Experimental" talk to your local FISDO after your test stand tests.

#### BoKu

##### Pundit
HBA Supporter
A friends son, was putting different chips in a modern VW, I thought these chips can be purchased in Hot Rod mags...
The majority of those tuner chips are crap.

#### rv6ejguy

##### Well-Known Member
Let's remember that tuner chips or reflashes these days, are still usually in the original car chassis. Remove the engine from a 2008 and up or so put it on dyno or test stand or aircraft without all the chassis sensors hooked up. Doubt it will start in most cases and for sure you are going to have lots of error codes thrown if it does start. A lot of cars have a digital key code these days so the ECU won't run the engine without the receiver or ignition lock in the loop.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
I know something about this too. Engine codes for GDI's are very complicated, with late injection (during the compression stroke) to prevent pre-ignition and other woes. To program one from scratch would require instrumented cylinders to identify the operation regions where late injection is needed and then to check that the injection profile is safe.

#### BobbyZ

##### Well-Known Member
A lot if it depends on the cars aftermarket support in the tuner community.I deal with VW/Audi and the Bosch ECU code is pretty much out there for the most part.I can also get software that is essentially a hack of the ECU that easily bypasses the immobilizer and factory settings and can rewrite the maps within reason.

Having said that I'd be doubtful that you could successfully adapt it to aircraft use and even though it is possible you would lose the ability to have quite a bit of redundancy that is needed for aircraft.

Now if all the naysaying hasn't scared you away yet there is hope.It's been found that you can convert most any direct injection back to a normal FI system with little performance loss (I've swapped a few VW's) and the losses can be gained back by more boost and fuel What is usually lost is the fuel economy and some drivability.

As far as redundancy goes it is not that hard to do with normal FI fuel pumps but it is almost impossible on a direct inject system unless you can add another engine driven pump.In a vw system I cant see it being done without redesigning at the minimum new cams and cylinder head so it would be a monumental undertaking to say the least.Whereas with a aftermarket style ECU you could relatively easily design a setup with a backup ecu and sensors.

Last but not least I'd hate to have those kinds of fuel system pressures in a gas engine stuffed under a aircraft cowling 10,000ft in the air but that's just me.

#### mel

##### Member
Hay all, From the late 1930`s through WW11 and the fifties DGI mechanical was used on the big round engines. Water was also used and both worked great. Those engines had no problems with altitude 30000 + feet. After it was figgered out the systems were reliable.

Mel