What Are Air Injectors?
Air injectors, are, as they sound, a set of injectors that inject air instead of fuel. They are commonly used to control the boost pressure output by a turbocharger.

What do they look like?
There are various types available, but the most common ones are as follows.

There are however many types available nowadays, including ones that only run a single injector.

How do they work?
The air injectors have an input to the top of them from the turbocharger and an output on the bottom to the wastegate. The injectors are wired to the ecu so they can be controlled.

The ecu air injector map is mapped against boost, rpm and air temperature. The injectors initially stay closed, keeping the wastegate closed too, encouraging the turbo to spin to speed as fast as possible. When the desired turbocharger pressure is aquired during mapping, the injectors are pulsed so that they open at that point, allowing air to flow to the wastegate. This of course opens the gate, bypassing some exhaust gas from the turbine wheel, slowing the compressor and leveling or dropping the boost pressure depending entirely of course on how much air we allow through. The beauty of this system is we can use a relatively weak actuator to achieve very large boost levels and we can accurately program boost curves into the system.

Any downsides?
Yes, if the injectors fail, due to the “Bleed On” configuration, the turbo will run whatever boost it can until something either stops it or something fails due to the fact we have blocked the pipe to the actuator.

 

i know you use air specific injectors, but why cant you use normal fuel injectors but without the fuel obviously?

is there a reason why?

 

Indeed there is.
A normal fuel injector is designed to have its coils cooled by teh fuel flowing through it. An injector like this will, and does, burn out in no time at all if left to operate only air.

 

Nice work Stu,

 

interesting stuff ive always wondered wot the hell air injectors were

 

cheers stu, answers my question lol

 

In your experience Stu , how many times have you seen these type of set ups fail, to give everyone the likely probablilty of such a problem

cheers

PAUL

 

i was gonna get some air injectors but opted for a turbo smart boost controller (not fitted yet)


which is the best way to go


the reason i got the boost controler was for reducing boost levels in the lower gears

 

Unbeatable IMO. Air injectors are old fashioned.

 

Just in case anyone doesnt know what "bleed on" means and its implications.

Basically the way the injectors work is that they totally and utterly STOP the actuator from seeing any boost when they are closed, so this means that until they are opened to "bleed on" (ie allow through them) some of the boost the actuator will never ever operate, its just like you have pulled the pipe off of it, so consequently you could end up running 3 bar of boost when you only want 1.5 bar, which is obvioulsy potentially very dangerous to the engine.

This is why some people are against the use of air injectors, because they dont "fail safe".

Typically people will notice if this happens though of course


Trouble is that if you want to eliminate "wastegate creep" by hiding the boost totally from the actuator, you have no choice but to accept that a failure will result in the actuator never seeing the boost.

If you use a "bleed off" type (like an after market boost controller does) instead and it fails, then it means that you will drop down to whatever your actuator setting is, which is obviously a lot safer.

 

one thing to remember on boost controllers is the soloniod response time as well as the boost threshold they opperate in when choosing one

 

In fact it is MUCH worse and allows far more boost than if the pipe was simply pulled off.

 

Oh, now this one we could have a discussion on, lol

Cause arguabley you are correct, in terms of the life of the engine.

But in terms of overspooling the turbo (due to leaking air from the pipe thats come off with no resistance), its actually not as bad, so it depends what you care more about, your turbo or engine

 

No no...
What i am saying is, if you pull the pipe off a -31 it will run around 32psi on your average YB engine, even if you plug the pipe.

If the air injectors fail on the same engine it will run 50 - 60.

 

Why?

Surely either way the actuator wont operate at all, so why the difference in boost?!

Yet again, your depth of knowledge exceeds mine im afraid Stu!

 

Well, basically, your 8psi actuator spring will hold the wastegate shut until the turbine housing pressure reaches or exceeds 8psi (Theoretical, as its different due to teh size of the wastagate penny).

However, with its the actuators signal connection blocked and airtight or with its slight calibrated bleed, 8psi pressure is not enough to operate the 8psi spring due to the depression that is created behind it within teh capsule and thus in essence, the spring rating is increased which is of course why you can run far more boost with air injectors in the first place.

Does that make sense?

 

oooohhh,thats a technical bit of stuff there! can you not have an emergency bypass? one that will induce beed off instead of bleed on? say if you plumbed in a switch that measured the pressure differential between inlet and exhaust of the air injector lines,if it goes above the level set it opens a valve which bypasses the injectors completely so youre running 0 boost (or whatever it would normally go to!)

 

i get it lol

so if no pipe on actuator then its at atmos, but with A/I vaccum stops it opening.

but 5 odd psi will make the car fast as fuck, for about 3 seconds lol

 

itd be like getting a hand pump for a bicycle and trying to pull the plunger with your finger over the end of the hose,then without!

 

Brilliant Vision, explains it perfectly.

 

would the bypass be viable for safety?have i explained enough what i mean?

 

Yes.
This is used quite often in racing, its known as a blow off valve and is simply a valve designed to open at a set pressure. Alternatively, you need some electronic way of cutting the ignition, or warning you, such as my Dynojet AFR meter.

 

nicely!they work a little different to how i thought so this was a good thread!glad it forced me to think of ways to get around the flaws too,i like subjects i can think about because im interested in them! are these solely ecu based?ie must they be run off the main engine ecu,OR could they be run off a separate module (ecu if you like) that simply monitors the engine parameters and alters boost accordingly.guess what im asking is,is this for p8 boys only?

 

Air injectors work with all levels of Weber Marelli.

 

 

Ive actually always wondered this! Thanks!

 

So effectively its just an actuator/bleedvalve all rolled up into one?

What are the advantages of air injectors? Do they help to hold boost better?

 

Always wondered the above ^^^ cheers for the info

 

Yet another interesting read Stu

Steve.

 

why can you not have a boost limit in the ecu so that if it sees, say 28 psi, tthen it cuts the spark?
then surely it won't overboost and blow the engine

 

You can, but your in the region of a greens conversion there and no one uses air injectors with greens anyway. The statement was aimed at folk running 2bar plus.

 

Good bit of reading that

 

Good easy to understand essay lol.
Always wanderd what the fuck they were and now I know. Cheers Stu.

 

that matters on wot / or who set the air injectors up.

as some i've seen have 0.8 or 1.2mm jets on the lower body of the air inj's, so any positive boost can escape duein gear changes, and also changes the amount of boost at same air inj duty in the map.

on mine i have no jet now, but the bottom alloy bolt on the air injectors bodie has a slight groove in the thread, so it still releases the positive boost when the air injectors are shut.
Mine are ford motorsport ones. dont know if newer ones differ.

if your cars runnin over 29.5 psi and mapped for this, and then the air injectors fail, your need a 5 bar map sensor to relieze this. as 3 bar map sensor only reads to 29 - 31 psi (matters on sensor)

 

very good read!

 

oooh they are my old ones

 

so when u going to discuss antilag then stu ?

reall intrested in runnig it in the future and was wonderin whats involved ?

gud job on the air injector discussion

bri

 

BTTT

 

Very good read this

So i understand what they are and what they are used for so say i now want to go and fit a set to my motor.

Say the car is running an Ahmed 803 set up do i just ditch the Amal Valve and use these instead?

Where dose the wiring come from, the oridinal plug off the Amal Valve? and is it spliced into two for the "2 injector" type?

Im guessing that once fitted it would involve a trip to the likes of you Stu to get them set up?

Thanks,

 

You will need a chip with air inj map built in.

and yes you just split the amal valve wiring into a pair of plugs.