sjordan

Ok guys,

For my upgrades I am told that I will need secondary injectors. So my question to everyone is this. What is the best way to control them?

I have heard that getting a ecu replacement is a bad thing.

Will the S-AFC be able to control secondaries?
Would the e-manage by Greddy be a better choice for controlling secondaries?

Also instead of secondaries could I just upgrade to 1600's? If I do this will the S-AFC be ok here?

NZConvertible

Depends on your upgrades. The stock injectors are good for nearly 300hp, but the stock pump isn’t. Why? It’s expensive yes, but not bad. Ah, now I see your confusion. You already have secondary injectors, which a lot of people upgrade. You already have two 500cc/min primary injectors and two 500cc/min secondary injectors. The 1600’s would be for the secondaries, but no, the S-AFC can’t handle much above 1000cc/min injectors.

sjordan

Ahh so doing something like a 1000cc on my secondaries would be fine with a S-AFC correct?

NZConvertible

What upgrades are you planning? What is your HP target?

Rpeck

Who says a S-AFC will not control more than 1000cc Secondaries? I'm not questioning you; I just want to know thats a fact, I planned on getting 1100cc injectors and using a S-AFC, should I scale down to 1000's? My ECU has been reprogrammed to run at 83% duty cycle, does that make a difference?

sjordan

Ok mods as of right now:

Street Port
Cone intake
HKS BOV

Mods this week:
Downpipe
TestPipe
HKS Catback exhaust
FCD
Walboro Fuel Pump
Cold Air Box

Future Mod:
Upgraded Turbo
Greddy FMIC
Electronic Boost Controller

So as you can see I am doing all those mod's this weekend I figure that I should do the fuel mods before I do the Turbo Upgrade.

So if you guys had this setup what would you do for fuel upgrading? I rather not run a Haltech.

BTW this is all on a 1990 TII and the engine was rebuilt about 7,000 miles ago by Don Marvel (marvelspeed.com)

NZConvertible

I seems to be the agreed on limit for FC’s. It’s to do with the size of the stock injectors and the fact that the S-AFC’s correction is limited to ±50%. The bigger the injector the more you have to tune them down, so if the injector’s too big, there won’t be enough correction available to get the correct mixtures, and it’ll always be too rich. You might get away with 1100’s, but don’t quote me... You’ve got that a bit mixed up, that’s not how EFI works. The duty cycle is based on airflow and RPM, and varies from a few percent at idle up to nearly 100% if you’re crazy. You shouldn’t exceed 80%; otherwise injector accuracy goes to ****.

Rpeck

What I was told is that; the stock ECU is programed to run a MAX duty cycle of ~55-63% A aftermarket, or in my case reprgrammed ECU can be tuned to raise the max duty cycle of the EFI system. My ECU is now programmed to run at a absoulute max of %83 duty cycle if needed. And that should only kick in that high if I run around ~18 PSI of boost. So if a stock setup is set at 60% duty with 550cc injectors and the S-AFC is tuned to at +/- %50 that would be a max of 1100cc’s.

However if the ECU is allowing %80 of the normal duty cycle, the S-AC at +50 should be able to control at least 1300cc’s worth of injectors. Does any of that make sence? Also I was told you should NOT exceed 85% duty cycle do to the heat produced only, The ND injectors RX’s use are very accurate to all extreems, but will not hold the heat of a constant high duty cycle.

NZConvertible

I’ve heard that too, but I believe RETed and others have proven this wrong. 63% is only enough for ~230hp, and many people exceed this with the stock ECU and injectors. I may be misunderstanding you, but I still don’t think you understand duty cycle (correct me if I’m wrong). It’s not “set”; it’s being continuously calculated by the ECU based on airflow and RPM.
If you’re installing larger injectors, you tune them down (reducing pulsewidth), to correct for their higher flow. To get the same quantity of fuel from an 1100cc/min injector as a 550cc/min injector, you’d have to use a –50% correction, which is the max the S-AFC can do. This will not give you the ability to go any leaner, so you miss out on some tuning opportunity. Factory tuning is always on the rich side, so leaning it out a bit means more power. I don’t think you’ve got this quite straight in your head. Running a higher duty cycle doesn’t mean the S-AFC can control larger injectors. True, except that all injectors become inaccurate past that, because the injector’s opening and closing time becomes a factor.

Rpeck

Well, I am not sure how much sense this makes, but this is what my head is thinking; Lets use 60% for the stock # and 80% for the modified ECU # .. just for simplicity.

Stock ECU set at 60% duty cycle no S-AFC adjustments = 550cc of fuel.
Stock ECU set at 60% duty cycle with full +50 on S-AFC = Control of in theroy up to 1100cc.

Modded ECU set at 80% no S-AFC adjustments = 660cc in fuel the 20% gives you another 110cc’s of fuel in theroy. More duty=more fuel right?

Modded ECU set at 80% +50 on S-AFC gives you 1320cc’s of fuel push. Or should be capable of contling close to 1300cc’s

Am, I comepletely off on how all this works? More duty pushed more fuel correct? More Duty + S-AFC should push even more fuel.?


I don't have a great grasp on EFI systems .. but his just makes sense to me. Isn't this kinda how stand alone systems can contol so much fuel? much the same way?

1FastT2

iTrader: (1)

I have to say that going stand-alone (Haltech) fuel injection was the best thing I have done to the car. It runs great and you never have to worry about running out of fuel. Im running 550cc primaries and 1600cc secondaries and it runs great . If your planning on doing alot more work to the car I suggest going this way, if not then a piggy back computer will be fine.

NZConvertible

Dude, you’re stuck on this idea that the duty cycle is a set number. It’s not! I’m also quite sure the stock ECU is capable of exceeding 60%.
The stated size in the injector (e.g. 550cc/min) is the flow you’d get if the injector is held open, i.e. a duty cycle of 100%. So if that injector is pulsed at 50% duty cycle, you should get around half that amount (275cc/min).
To correct for larger injectors, you need to make the engine think it’s getting less air than it is so it reducing the pulsewidth accordingly. So if you replace the 550’s with 720’s, without correction you’ll get 720/550 = 31% too much fuel. By telling the engine it’s only getting 550/720 = 76% of the air it actually is (by applying a 100-76 = -24% correction) the amount of fuel injected is correct. Note that the duty cycle is completely irrelevant in this calculation! It’s only the size of the injectors that matter.
1100cc/min injectors would require a –50% base correction, before any tuning is done. But you won’t be able to tune them down any further, which might be a limitation.

Rpeck

I KNOW the duty cycle is not a set number. I was just using set/round numbers for simplicity. But the MAX duty cycle is, I am sure very close to a set number. I think I am going to go with 1000cc injectors to be safe. I am damn glad I haven't ordered them yet. I am ordering them on Wendsday of this week.. Doa!

I understand what you are saying & I am alot more clear on this subject now, thank you.

Now in saying that I still have the idea that; even if a aftermarket ECU only gives you a 10% boost in duty cycle .. that is 10% more Fuel! correct?

Or does duty cycle incorperate the A/F mixture into the equasion? If I have a higher "max" duty, is the system going to put in a higher load of air? or is it just putting in more gas? Now I am speaking it terms of optimal MAX duty cycle.. i know the injectores are NOT stuck at 80%

NZConvertible

The ECU doesn’t use duty cycle; it calculates a fuel injector pulsewidth, i.e. the duration it will be opened for. Put very simply, the ECU measures the amount of air and the RPM, and then looks up its maps to get the pulsewidth the tuners decided was required for the appropriate A/F ratio. There are also corrections applied for temperature and pressure. It then opens the injectors for the amount of time required.
The duty cycle is just the percentage of the time the injector is open. At 6000rpm, one revolution takes 10ms, and the injectors are fired once per revolution. If the injector pulsewidth is 3ms, that’s a 30% duty cycle.