View Full Version : 4cyl + FAST efi + boost = 8 injectors? (got questions)

02-03-2006, 08:39 AM
I'm trying to wrap my mind around this turb0'd Ecotec 4-cylinder project, and need some help as well as some questions answered...

I've got a FAST efi setup (pre-XFI version) and I'm trying to figure out how to manage the fuel while under boost. I originally was gonna use the stock GM harness and piggyback a seperate "Portfueler" setup, but I found out I can't use the regular GM harness/ecu, and a modified to work harness/ecu is gonna cost me another $1300 and is not programmable. I was wanting something that would kick in an additional set of injectors whenever the engine starts seeing boost, so I called FAST to see if my unit could do that...they transferred me to one of their tech guys in Michigan (a Dave H? I think) and he said "no", but recommended running 2 sets of 4 injectors of the same size, firing together. But I guess my question is, I've read of guys having horrible idle quality and fighting injector sizing because they were trying to get one that was big enough up top while keeping the idle happy? Will I be in this same boat, or will a dual set of 4-injectors get me where I need to be?? This is my first foray into EFI, so be gentle...

(Oh, and by talking to the guy supplying my turbo hard parts I'm hoping to see ~30psi and 500hp with this combo when I crank it up for play time.)

Fuelie Fan
02-03-2006, 10:09 AM
He told you that? I can't say that I agree. If you're not staging them, Having two 35's or one 70 (numbers for reference only) per cylinder will result in the same commanded pulsewidth and therefore the same idle quality issues.

Generally, It's not the SIZE of the injector, it's the length of the pulse that affects idle quality.

Say you have two engines, one's a 454 making 500 hp N/A and the other's your engine. Since injectors are sized by peak hp requirements, they will need the same injector size (if you run two sets of 4).

The 454 has a lot of cylinder to fill at idle, and also is probably decently efficient at low rpm's, so it's going to need a larger percentage of the injector's max flow rate to idle. Your engine, on the other hand, has tiny cylinders, no boost, and probably is less efficient at low rpms (I'm figuring your torque/hp peaks are higher in the rpm range). So, your engine needs much less fuel at idle, which means very small pulsewidths.

Injectors are not perfectly linear. If you only apply voltage to them for 1 microsecond, the pintle will never open. In fact, most injectors have a minimum of nearly 1 millisecond. that's when it just STARTS to flow any fuel. It takes approximately 1.5 ms for most injectors to become repeatable, some as much as 2ms. If your fuel requirements results in pulsewidths below 1.5ms, the fuel delivery will be unsteady and hence you have a rough idle.

02-03-2006, 02:01 PM
That doesn't sound very promising. Great, I was trying to avoid redundancy (from both a price and complexity stand point) but it sounds like a piggyback system might be in my future unless I can find a workaround...

02-03-2006, 02:49 PM
Hey, didn't you post a while back that you were gonna start playing with an Eco setup? Ever get a tunable ecu/harness up & running?

Fuelie Fan
02-06-2006, 10:51 AM
The company that I was working for folded. however, an ex-customer is picking up the pieces (he bought all the equipment and IP) and trying to put something together, I don't know if Ecotecs will be part of his plan or not. I may do some contracting for him.

I have an ecotec sitting in storage, basically untouched. I got spark working one night, then found out I had other priorities (finding a new job) the next day.

02-07-2006, 04:44 PM
I talked to a couple more efi companies today...and they told me the same *2 sets of 4-injectors* story...not staged, running 8-inectors. And I have yet to find a setup other than the GM/Delphi Mefi setup that will function with the stock Ecotec crank/cam sensors...

Bummer about the job, FF...I hope you land on your feet!

02-07-2006, 05:50 PM
You might want to give these guys a call:


I lifted this from their website
Injector Compatibility

SDS will drive most low impedance (1.7 to 3 ohm) or high impedance (12 to 16 ohm) injectors. The injector impedance must be known when ordering so that we may supply the correct injector drive harness for those injectors. The system is intended to work with port type injection only (one injector per cylinder) or for some 4 cylinder high boost applications, SDS can drive 2 injectors per cylinder if they all have the same impedance and flow rate. This is called the staged injection option.Please note: we cannot supply injector connectors for late model Japanese cars using non-standard Bosch type connectors. We can graft on your old ones if there are a couple inches of wire left on them or the user can perform this work.

I have used their system on some turbo cars and found them to be knowledgable and friendly.

Fuelie Fan
02-08-2006, 08:38 AM
Well, I must be missing something, because I can't see how it'll be a big improvement if they're firing at the same time, for the same length of time. MAYBE because the second set is further upstream? MAYBE because you get a better "average"? By this I mean that, being below the repeatable pulsewidth limit, on any event one injector could be provide less than expected, but the other could be injecting more than expected, and the net result is, on average, the amount that you expected? Pure conjecture. I'm going to have to think about it some more.

I've used SDS systems before, I don't recall them having a TRUE staged injection control, what they are describing is the same as what Chevy454 has heard from others.

I seem to be outnumbered on my opinion, so I guess all you can do is give it a shot.

I've heard that Haltech can control the Ecotec directly using the stock crank sensor.

02-08-2006, 09:58 AM
FF: I hear ya totally, man...I know little about efi but what you says make sense *to me*. Also, didn't mean to come across above as saying one way was right/wrong, just relaying messages...

Fuelie Fan
02-08-2006, 03:44 PM
Wasn't taking offense, just being humble about my skills and experience. If so many other people are recommending it, there's probably some benefit, but I have a hard time seeing (in my head) how it will be worth the hassle. I'd definitely have to see it in action before I spent the time to modify my intake.

Thanks for the well wishes, by the way. I did get a new job down in Southern California with a company called MillenWorks, which is pretty cool but completely different from what I used to do

02-08-2006, 04:26 PM
My bad, I thought the SDS could be operated in a 'staged' set up. It seems to me that someone would have come out with this by now...Let me see if I understand you correctly...You want to run say a 500cc injector (sorry I dont know what that converts to in lbs.) for good drivability and idle qualities.... When boost kicks in a secondary set of injectors would fulfill fuel requirements. Am I on the same page as you?

02-08-2006, 05:35 PM
Right on, Patrick...

Fuelie Fan
02-08-2006, 06:12 PM
There's a few companies that have true injector staging. I don't have my demo software packages with me, but I'm pretty sure motec, haltech, autronic, and AEM all do. Possibly EMS as well. Not sure about Big Stuff, never used it.

03-11-2006, 02:04 PM
I think the newer injectors are more capable of good idle at low pulsewidths than the injectors from a few years ago.
You may be able to get by with just a single set of injectors. Increasing fuel pressure with boost should help, though it is considered a crutch.
Have you tried looking at what GM uses? I think they are working on some turbocharged Ecotecs, maybe they've got a simple solution?