View Full Version : Injectors

17th August 2000, 22:04
Could some one tell me the colours of the scooby injectors and which MY they came from , as I`ve been advised to get a set of STI3 injectors for my STI2 .
Cheers Dave

20th August 2000, 15:23

the standard STi II injectors are grey, and will flow about 380cc static. This is not sufficient for high power (OK for torque though).

You can get some yellow injectors, they'll flow 480cc and you'll be fine for some serious power. I wouldn't go beyond 350BHP without doing some internal work... also flowing the headers will allow you to make more power for the same boost :) If you want to go mental, you have a good starting point, the EJ20G closed deck block used in the STi II is one of the strongest Subaru ever made; with good internals and a some careful attention to the heads you'll be OK for 400BHP. To safely put out that kind of power, I'de recommend you upgrade the fuel system and get fit 550cc injectors (interestingly yellow!)

There are also some other yellow injectors, 440cc flow but triple spray, which might be worth a look, used on the later STi cars, but they may not fit your fuel rails; Bob has more details on this :)

Hope this helps,


Bob Rawle
20th August 2000, 21:24
Later Phase 2 injectors definately won't fit, standard STi3/4 injectors (440 as Pat says) or twin turbo legacy injectors (480cc) will fit straight in. Don't forget to release the fuel pressure or you will hydraulic the engine.

When you look at the data log check duty, map, rpm and tp. If you are running version 6 software then there are a couple of extra logs that will help there. Relate the above together, duty should not exceed 85%, on your car you will be struggling over 1.25 bar I think. Don't try and run it at anything higher than 85% duty until you get the injector issue sorted.


[This message has been edited by Bob Rawle (edited 20 August 2000).]

20th August 2000, 21:34
At idle, what kind of injector on-times to EJ20 see with 550cc injectors? 480cc? Just curious.


Bob Rawle
20th August 2000, 22:19
Shiv idle injector on time is next to nothing .. 1% duty or less whatever the injector rating, whichever ecu is used (assuming its mapped properly)

With all the tuning you have done is it different over there ?


21st August 2000, 05:09
Bob-- I was asking what the injector on-time was at idle with those various injectors. The answer should be in milliseconds, not in percent. Bigger injector, less on-time.


PS. I'm asking for typical on-times. Presumably viewed through a Link monitor screen. Assuming proper tune, of course. What's the confusion?

[This message has been edited by shiv (edited 21 August 2000).]

Jan Shim
21st August 2000, 07:43
Pat / Bob:

any idea if the Link ECU supports 550cc injectors ? Has anyone tried these with the Link before ... i've been told that idle might be difficult to tune and i'm prepared to take that risk but i must know their compatibility with the Link.

Pat, my Ver 4 Japan spec WRX block according to the VIN plate is EJ20GDW6NE but an identical engine from the same model was removed to fit JUN Stroker Kit and the blocks didnt look closed deck to me, even the dealer didnt think it was.

21st August 2000, 08:47

If someone spills the beans regarding injector on-times (at idle), we can figure out if the 550s will introduce idle problems. And what needs to be done to solve them.


21st August 2000, 09:15

Sorry, I'm not an expert on injectors but I don't think there should be a problem with running 550cc injectors if the ECU is tuned properly. I am currently running 550cc injectors, Skyline BNR34 fuel pump, and a custom tuned HKS F-Con V Pro for ignition and fuel curve tuning on my STI Ver IV..

21st August 2000, 18:53
Thanks for the info guys , now for the next question anyone know where I can get hold of a set of either STI3/4 or twin turbo legacy injectors (pref second hand if they cost too much new)? also how much are the said injectors?
Cheers Dave

Bob Rawle
21st August 2000, 19:28
Jan, you just use exactly the same procedure to set up 550's as any other size, adjust master to get the required resolution in the zones whilst not exceeding 80/85% duty.

Obviously the bigger injectors will have a courser resolution and this is why idle setting may be more problematic.

Dave, Subaru dealer is the best bet. Part no for legacy twin injectors is 16611AA231

No confusion Shiv, genuine question, Link works in duty, can work out the pulse times but no real need as any size injector can be adjusted in. Wondered if your techniques were maybe different to ours somehow.

Closed deck blocks not general after MY96 afaik Jan so not suprised to hear it was not.


21st August 2000, 20:43

The reason I was talking in on-times is because that is standard when discussion the injector activity in itself. For high resistance injectors, the minimun on-time that they can reliabably operate at, without binding up (stalling) is, depending on design, 1.7-2.2ms.

Low resistance injectors (used without ballasts), on the other hand, can operate down to 0.9-1.2ms.

If one is experiencing a overly rich idle that cannot be tuned out, it is more than likely that he is brushing against the mechanical inefficiency of the injector. It cannot pulse any shorter, despite directive from the ECU. This, as you probably know, will NOT be displayed on the Link engine monitor screen, which assumes that the injector has no such mechanical limitations. It is only appearant to the user during tuning (i.e. if you go any leaner with at idle, the engine speed with bounce and, at times, even stall).

When this point is reached (and i suspect it will be with 550cc high resistance injectors and stock injector drivers), there are a few solutions:

1. Live with an overly rich idle and possible cat failure/clogging by setting the min. injector on-time setting (if so equipped) to 1.7 to 2.2ms and a/f ratio targets richer.

2. Raise the idle speed.

3. Upgrade injector drivers and install low resistance injectors (no ballasts).

All things equal, a set up equipped with low resistance injector drivers can run 40-50% larger injectors before running into low speed driveability problems.

Just figured I'll tell you where I was coming from with all my questions...


21st August 2000, 22:08
Thats nearly word for word from the RC guys.. http://bbs.22b.com/ubb/smile.gif

Indeed you are correct Shiv...

Most guys who run larger injectors or aftermarket ecus over here dont run cats anyway...*we are rebels* haha

But I will let you know about the crappy 550 injectors I have... as I will be fitting them soon http://bbs.22b.com/ubb/smile.gif


Bob Rawle
21st August 2000, 22:22
Thanks for the explaination, when you talk about stall assume you are meaning electrical not mechanical, 12 ohms is not that high, used to work at 20/23 when designing abs solenoids, coil charge time is the culprit though. 480 cc injectors at 30/40 percent more fuel pressure works ok at idle with Link so I guess that bodes well for 550's, J ... hurry up and put them in and lets see ... for real mapping fun fit a 3 bar map sensor maybe ?

Link idle normally shows injector duty as zero, the master modifies the injector base pulse width but as you say there are limits. Pays your money.


21st August 2000, 23:03
Just a couple of data points:

Both my 1.8 turbo Miata and 2.5L turbo Impreza run 550cc low resistance injectors. At a reasonably stoich 750rpm idle, the Miata sees on-times of 1.0-1.1ms. The big block Subaru sees on times of 1.1-1.3ms, both well below the typical min. on-times typically associated with high resistance injectors. I suspect that a 2.0L EJ20 will have some idle issues when using high res. injectors. Then again, if you guys aren't running cats, I suspect you don't care about running rich at idle. In the US, we get fined rather heavily if we prove to be "gross polluters." Forces us to be a little bit more environmentally-minded. Most of people I know tend to complain when they smell noxious gas fumes at idle.

As for mech. vs. electrical inefficiency, it depends on which end you look at-- actual disk/pintle movement or the force which drives it. Like two hands in a hand shake.


Jan Shim
22nd August 2000, 06:42
Shiv, why do you say running rich is ok if we arent running cats ? I do not have a single cat in my 3" exhaust system but i'm still worried about something called Bore Wash where excess fuel floods the bore.

Before i knew about this term and its effects, i couldnt care if my LambdaLink was showing 3rd green during idle but these days i am more careful and able to get idle to amber or no lights depending on electrical loads.

Bob, is this something i would expect with the Apexi 550cc injectors ie difficulty to balance between stable idle and lean idle ? At present with my 380cc ones, values for Offset, Volt, 6 idle zones (Fuel & Ignition) and IAT have to be kept low in order to enjoy a lean idle. The trade off is the RPM needle hunts for about 5 seconds each time i start the engine. http://bbs.22b.com/ubb/wink.gif

22nd August 2000, 07:25
Hi Jan, it's true that bore wash can eventually lead to excessive cylinder wall wear and reduced ring sealing. The excess fuel literally washes the lubricating oil, causing slight metal on metal contact. As I understand it, this is a big consideration for cars that experience long durations of sustained rich run conditions. But unless you intent to let your car idle rich for long periods of time, I don't think it will be a problem. Then again, I'm not an expert on this situation. I do know, however, that this is a serious consideration for many serious engine builders.


22nd August 2000, 12:24
Hey Bob...

So you like a challenge ? http://bbs.22b.com/ubb/wink.gif

I've had the 3 bar MAP and 550's for ages.. just need to get around to fitting them...

And after the fun with Marks car *cough*.. it should be interesting... lol

In relation to idle.. I think my car would be the prime example to use... 550's... upped fuel pressure (albeit slightly)... MAP sensor... light weight flywheel..etc...

Shiv.. you are right about bore wash.... but requires a lot of fuel ... most of the fuel is ignited/burnt anyway... its only when the fuel mixture becomes really saturated it comes a problem. http://bbs.22b.com/ubb/frown.gif

But yeah.. something to consider...


Jan Shim
22nd August 2000, 13:08
How much exactly is your definition of "a lot of fuel" Looking at the LambdaLink, if at idle the last green light (AFR 11:1) is on permanently, would that constitute a lot ? http://bbs.22b.com/ubb/confused.gif

22nd August 2000, 20:23
That firefoxs is full of it.

22nd August 2000, 21:08
Indeed.... http://bbs.22b.com/ubb/biggrin.gif

And everyone believes me... haha


22nd August 2000, 21:36
Siv...if there was enough unburnt gas at idle to actually pemit bore wash, would you not foul the plug first before ever doing damage to the motor/

ane yes, 11:1 is a bit rich i'd say!

Firefox...how come your bank is taking so long to get bak to mine!?!

23rd August 2000, 00:23

Not really. You can still run with fouled plugs. Depending on the fouling severity, the engine would typically misfire under load. If this wasn't the case, there would be no such thing as bore wash http://bbs.22b.com/ubb/wink.gif


23rd August 2000, 14:02
Hi all!

the "problem" with big injectors is that they are big :) But seriously, it takes time to open an injector; there's no point in providing a 0.2ms pulse to it because no fuel will come out! So, typically you'de expect a pulse width of about 1.6ms at idle (depends on the injector, of course).

The problem is that the injector opening time is not a constant, and varies as a function of battery voltage.... in order to reduce the error in fuelling, the pulse width must be long in comparison to the standard deviation of the injector opening time... in case this isn't clear, let's say there's a 0.1ms standard deviation and the typical value is 1.3ms to open. If the pulse is 1.6ms then it could supply 0.2ms (if it takes 1.3+0.1=1.4ms to open) to 0.4ms (if it takes 1.3-0.1=1.2ms to open) worth of fuel, that's a huge error (like, err, *double* the amount of fuel)! Now assume that the pulse width was 3ms, then fuelling time would be 1.6 to 1.8ms, much lower error.... but far too long for idle.

The same applies to injectors whether they be large or small; but of course a large injector will flow more fuel in the same time. A long-ish pulse on a small injector may well give the right amount of fuel, whereas on a large injector it would run rich. I've seen an AFR plot of an engine at idle, scary stuff... AFR varies between 10:1 and 17:1 with the same pulse width (but of course different opening times).

The problem is agravated by homogenisation / atomisation problems at idle... the fuel pressure regulator will drop the fuel rail pressure on manifold vacuum to reduce the amount of fuel injected to try to cope with this limitation of the injectors, but this in turn increases fuel droplet size. You can't really win.... well, you can user EGR to give a better burn at idle... more charge means better swirl and squich, but there ain't no EGR on UK Scoobs..... you could of course use *TWO* injectors per cylinder.

When using two, a small one may be used during idle / high vacuum. This will not be able to flow a lot of fuel but it doesn't have to. Then when the loud pedal is prodded the injector time on the small (or primary) injectors will rise. Once it gets to (say) 13ms the time may be cut back drastically, as the second set opens up as well. Because the primary injection time is reduced drastically, the secondary (large) injectors don't need to operate near the high error point, they can go straight in at, say 5ms, where error is quite small. Getting a good balance in the transition region is tricky, but once setup it will provide the best of both worlds, good atomisation at idle with a fairly consistent charge, but also flow a bucketload of fuel under full chat :)

Another feature that may help idle quality is air assisted injectors. Basically, idle air comes not through the main manifold branches but through little enclosed channels which open just above the injector. This increases air velocity at this point and can be very effective at improving atomistaion and mixture homogenisation.

To get a good idle with 550cc injectors in an EJ20, it would be necessary to raise the idle to 1000RPM, maybe more, and run highly retarded timing, so that the amount of charge being inducted is quite large (compared to standard); this would allow the required injection pulse width to be supplied without over-enrichening the charge. It doesn't make efficient use of the charge, but at least it won't idle like a dog or wash the bores. It will heat the manifold more than standard, though.

As always, what I've said could be complete and utter cobblers.... treat accordingly :)



23rd August 2000, 15:25
Be very careful about too high an idle speed, been there done that, had trouble getting an MOT!

Ok if youve got a friendly MOT station, but I didnt have, and they always saw the 1300 RPM idle as a way to get some work.

Not sure what the max allowable idle speed is, but its there to do with the emissions testing.


23rd August 2000, 20:51
16611AA231 is stock frozen at english dealers but quote 102.60+ vat each

25th August 2000, 14:19

Can your lot (GGR) get hold of these injectors, and, if so, how much would they be?


29th August 2000, 06:29
Shouldn't be a problem, they will have to come from Japan. Call me at work or mail me.
You do know that that part number is for WRX and STI v3,v4,v5 and 22B don't you.

29th August 2000, 17:18
Thanks Simon. http://bbs.22b.com/ubb/smile.gif

I am looking at other injectors at the mo because those ones would be a fairly expensive way to get less than 10% increase in capacity. If I'm changing the injectors, I would want to get a set with more... what's the word... hmmm... potential. http://bbs.22b.com/ubb/smile.gif


29th August 2000, 20:30
You didn't ask me?, How do you know they are too expensive?

31st August 2000, 11:40

I wasn't meaning any offence, honest. I have been quoted a price of 102.62+VAT each injector from subaru uk, I just assumed that these parts will cost a similar amount through GGR... My point was that spending the best part of 500 in total to gain less than 10% increase in flow seems quite expensive.

Of course, if you can get me the same part for significantly less then I would be happy to hear from you... maybe you could post me your price off-line? http://bbs.22b.com/ubb/smile.gif

Again, sorry, I wasn't having a go at you guys there. http://bbs.22b.com/ubb/smile.gif