Multiple injectors per cylinder

Right,m this is something I wondered about before and as Kev just mentioned it in the engine management thread I thought I'd pose a few questions about it.

I can see lots of benefits, running smaller injectors so idle and off boost fueling can be controlled more accurately is the main reason this interests me, but is there a proper standalone that could control this? Could you have it run 4x injectors up to certain revs/manifold pressures and then switch to 8?

Any disadvantages?

Yes Emerald can do it so the manual says! Usually only employed when the big injectors lose resolution at idle.

Yeah quite a few standalones can do it, against rpm or MAP, or both. Some will also fire the second set sequentially.

There are some REALLY good injectors around at the moment, which perform very well at low pulsewidths, so you may not need to go twin injector

kevhaywire wrote:There are some REALLY good injectors around at the moment, which perform very well at low pulsewidths, so you may not need to go twin injector

Are their cost prohibitive though? I mean would it necessarily be better to run one set of injectors over two?

Are there any other reasons, apart from smoother idle, to running two sets of injectors? I saw a mk2 with and S2 lump in it on another forum last night and the guy had the standard in-port injectors but additionally 5 further injectors that were actually mounted in the plenum, opposite where each of the runners were. I'm unsure of how you could actually be sure that the fuel from those additional injectors would actually be evenly distributed into the cylinders, especially when forcing the air in there with a turbo...

Also a custom 8 injector rail would be needed.

The old RS500 Cossies used to come with 8 injectors as standard, but that was purlely to bollock enough fuel in there to get the 500 odd hp required by the track cars...not even sure if all the injectors were rigged up on the road-going versions. They had a pectel ECU, L6 I think. I'm sure there's plenty of stand alone ECU's out there that can fire 8 injectors in pretty much any order you fancy.

Yea plenty can do 8 injectors and the cossies did use the Pectel ECU and the RS500 did have the 8 injector rail but they are like rocking horse poo.

mrbeige wrote:Are their cost prohibitive though? I mean would it necessarily be better to run one set of injectors over two?

Not that expensive imo. Most common injectors can be had for around $65. The Bosch EV14 is currently one of the best injectors around and it's not expensive from the US. Snake tongue spray patter too, so ideal for your 16V head.

One set of injectors is always preferable to 2 sets. Less chance of fuel leaking, less chance of injector failure, easier wiring, easier plumbing and easier intake design, not to mention easier mapping. There is a transition in the second set of injectors kicking in, which needs to be carefully mapped so it feels seamless to the driver.

mrbeige wrote:Are there any other reasons, apart from smoother idle, to running two sets of injectors?

I still think it's viable with K jet valvers. If you're going standalone, then I wouldn't bother personally. Back in the 70s/80s, injectors were pretty schitt by today's standards and they were forced to use 2 sets. OEMs have now pushed injector technology so far (because of emissions), you can get a high impedance 1000cc Bosch EV14 to hold a 14.5AF idle on a 1000cc bike engine with < 1.8ms pulsewidth.

The EV14 is used in the new M5, M3 engines etc, to name but a few:- [You must be registered and logged in to see this link.]

There is a MUCH better injector now though, the Denso 1220. It's a brand spanking new design and is being used in the 2009 Mazda RX8. It's atomisation is seriously next level. The finer the fuel atomises, the more fuel is burned (instead of wasted washing the inlet walls) and the smaller injector you can use.

I've got a set of 1220s on order The tips need modifying though to hold the O ring captive, but it's nothing major. I'll dish the details when they arrive.

mrbeige wrote:I saw a mk2 with and S2 lump in it on another forum last night and the guy had the standard in-port injectors but additionally 5 further injectors that were actually mounted in the plenum, opposite where each of the runners were. I'm unsure of how you could actually be sure that the fuel from those additional injectors would actually be evenly distributed into the cylinders, especially when forcing the air in there with a turbo...

I would imagine the boost would blow all the fuel to the furtherst cylinder from the throttle? He must have some kind of ports inside the manifold? Or he could be using pencil stream injectors that atomise upon impact with the valve?

$65 dollars isn't overly expensive as it goes, basically about £150 for a set of four, that you known to be good.

cheesey wrote:I would imagine the boost would blow all the fuel to the furthest cylinder from the throttle? He must have some kind of ports inside the manifold? Or he could be using pencil stream injectors that atomise upon impact with the valve?

That was my first reaction, very lean on the cylinder closest to the throttle. I've got a feeling I saw a melted piston on that thread somewhere too, that would suggest he actually had that issue.

Yeah, you need some guide of mechanical guidance with secondary injectors. Simply blasting them into an open plenum is problematic!

2 banks of injectors was as mentioned before an old skool method of tuning. Due to early day primitive spray patterns causing poor atomisation on cars requiring large cc injectors at idle and low rpm operation the bad spray patterns of the larger injectors on low duty cycle would cause fuel pooling in the manifold. This was subsequently overcome by running a bank of small cc injectors close to the cylinderhead port for idle and low rpm use, switching over either partially or fully to a second bank higher up the intake runners once port velocity was high enough to help atomise the poorer fuel spray pattern.
Realistically with todays advanced injector technology you can comfortably map a nice idle and low rpm with big 1000cc+ injectors no longer requiring the extra need for 2 banks.

...That well maybe but they still look the bolloxs when fitted onto the engine:D .
I rigged the Pectel super 8 ijection system onto my turbed
'raddo,the Weber/iaw is still 1 of the best injection systems out there IMO.
I bought the system off eBay last year, Weber L8 ecu,Pectel sub loom,
sierra Cosworth 4x4 loom for £550,8 injectors robbed off a mate's
scrapped Volvo T5 (Bosch orange top 335cc injectors) free,Lancia delta
int. EVO-1 inj. loom,free.(i decided not to use the sierra loom as my car was already running iaw,loads more work involved.
Ok,there's a bit involved regarding fitting the various sensors,crank chopper pulley etc but it's not rocket science and remember,if you buy 1 of the newer injection systems you ALSO have to map the bugger aswell involving the use of a rolling road adding ANOTHER $3/350...
something that isn't needed when using the ecu off say a delta EVO-1,
or even the older HF 1600cc twin-cam turbo delta.

Good work, but the average person new to turbos isn't really going to know all that stuff by name or understand it enough to simply go onto ebay and buy it.

I personally feel there is no need for all of that when 1 box, 1 loom and 1 set of injectors fullfills all of the requirements.

I've played with Pectel and Motec ECU software and it's deliberately horrible in a "we can send one of our race consultants to you at £500 p/h to help set it up" kind of way.....

Pectel is for racing cars on racing car budgets.

The rest of us use lower grade kit and get just as good results.