I believe the SAFC can control injectors up to 50% bigger than stock right? At least that's how the Honda guys figured it...so a car that had 550's can control up to 825's in theory.

 

No. With an s-afc, a car that had 550cc could run 1,100cc. (550cc / (50%) = 1,100cc)

I had 650cc injectors on my Mitsu 3000GT VR4 (stock injectors were 360cc).

(650-360) / (650) = about -44% correction. (which was around where I was at on my s-afc).

 

I don't know where you are getting your math from but I am not understanding it.

50% of 550cc = 275cc. So the answer is 825cc. You are putting in 200% of 550cc to get 1,100cc.

Jonny

 

Thanks for your concern, I am well aware of the w-58 "threshold" and have no immediate desire to explode it. On thread topic and for the moment I've got fuel issues: Do they fit existing 2jzgte fuel rail or do I need another rail?Like your sig numbers, w58, T67 putting down 464 @20psi (on CA 91oct?) A good target for me.

Thanks guys, a couple of choices, that exactly what I needed to know.

 

How you get precision 650cc that fit with the stock fuel rail? Do you know have parts # for it that would fit for the gte fuel rail? Let me know. I've been looking for new injectors that fit on the stock rail.

 

825cc injectors: (825-550) / (825)= -33% correction, theoretically.

550cc is 50% of 1,100cc.

Double the stock injector size. at -50% correction on the s-afc, u could run 2x larger than stock injectors. I'm speaking from experience.

I ran 650cc on my 3000gt, controlled by an Apexi S-afc. Stock was 360cc.

(650-360) / (650) = -44% (which was approximately the correction I used on the s-afc).

Get it?

Tell me I'm wrong.

 

I didn't say you were wrong - I said I didn't understand your math. So thank you for explaining it so I could better understand, but then you decided to be a **** at the end. Way to go

Jonny

 

(New Injector - Original Injector) / (New Injector).

(825-550) / (825) = -33%.

Although the car has larger than stock injectors, by using a -33% correction on the s-afc (give or take a few percentage at each RPM point) the ECU still "thinks" it's got stock injectors. 67% of 825cc is 550cc.

Eh, it's difficult to explain. Sorry if I was being an ***.

 

I wasn't saying that they could handle 200% of the stock size, but rather 150%. So a car that came stock with 550's could handle 825's...I don't see what you two are arguing about.

 

Your math is completely wrong. Sure 550 is 33% smaller than 825 but 825 is also 50% larger than 550.

(825-550/ 550) x 100% = -50%

100% of x = x * 1.0
90% of x = x * .9

...and so on. It also goes the other way so that

110% of x = x * 1.1

Something 50% larger than 100% is 100% + 50% = 150%

When you divide x / the % or in this case 50% what you're really doing is x * ( 1/.5) which becomes x * 2 which is clearly wrong.

The point is you got the values mixed up as to what plugs into where with your percent error formula in relation to what you're comparing.

 

Yup you're math is completely wrong.
550cc / 50% might be 1100cc but thats not the right calculation; you're basically calculating 200% of 550.

50% larger injectors is from the perspective of the original injector size. at 550cc stock injector mapping; 50% bigger injectors is 50% OF 550cc tacked onto 550. So its 775cc since 550/2 = 225, 550+225 = 775
At 330 it is 495 since 165 is half of 330.

Thats cool you ran 660s on your VR4 with such small stock injectors, that doesnt make the math right unfortunately. Running rich is doable, running lean is not. In fact the car will autocompensate to a large degree when under closed loop.

 

The ECM will compensate +/- 20%. It also has short term and long term fuel trim. ST is +/-10% and LT is the full +/-20%. When ST exceeds 10% it affects LT. You can check this by measuring Vf. If the ECM thinks no adjustments from the factory settings are needed, Vf will be 2.5v. +5v is rich and 0v is lean.

Most importantly - these trim factors get applied even in open loop, so whatever the O2 sensor tells the ECM in closed loop, the ECM applies in open loop. This is why it is so challenging to get a Toyco ECM to leave the fuel alone after you trim it with a piggyback. If you try to trim fuel in closed loop, it just adjusts ST or LT (or both) until you are back at stoichiometric, AND it applies that same factor when you are in open loop, so all your tuning results in a net gain of zero. This is why they have a TPS input - so you can make WOT/open loop changes without having the ECM correct.

 

I got that info from 3SI (3000GT forums). I used those calculations on my 3000GT, on a handful of other 3000gt's, on my brother's eclipse turbo, on my friend's SC300, another buddy's turbo eclipse, a couple MR2's, and some other cars as well. I'm not saying i'm a pro tuner or anything, but I've installed and tuned numerous cars with an s-afc successfully over the past few years.

If my calculations are, in fact, wrong- then how was I able to successfully control 650cc injectors on my 3000GT VR4? (stock size = 360cc).

There were guys on 3SI running 720cc injectors on their VR4's. 720-360 divided by 720 is 50% correction- which was in the ballpark of where they were at.

When I had 550cc injectors on my VR4, I was at -34% correction or so. When on 650cc injectors, I was in the -43% or so. When my buddy was on 720cc injectors, the s-afc was almost maxxed out to -50%.

Car ran just like it did when it was stock. Stoich a/r when it was idling, cruising, and low/partial throttle- and a solid A/R when i was at WOT and full boost. Not too lean, not too rich- just right.

I was under the impression that the percentage of negative correction was:

(New Injector cc- Old Injector cc) / New Injector.

I'm speaking from personal experience(s).

 

http://www.team3s.com/FAQ-AFCtuning.htm

I used this as a basic reference when installing an apexi s-afc on my VR4.. back in 2002

 

Actually, using an SAFC to control large injectors does "work" to control JUST the A/F at a basic level, but you need to understand what's going on beyond the A/F that you're correcting. Since the SAFC doesn't control PW, and only alters airflow, you're gonna run into much bigger problems with too large an injector, and that's timing advance. The stock ECU has timing maps that are ALL airflow based. The less airflow the ECU sees, the more it'll advance the timing. So while you can look at the A/F and be at a perfect 11.5, if you pull out too much airflow, the timing will advance itself A LOT. Pulling out 50% fuel on an SAFC is dangerous, and most people don't even realize that the cylinder pressure is increasing because they don't know what the SAFC is doing when used under conditions like that. If you're going to use an SAFC to tune with very large injectors, use an AFPR to basically "trim" the injectors capacity at WOT. The drawback to this is that the bottom portion of the map becomes hard to tune, but I'd take an erratic idle over a blown motor any day of the week. I do professional dyno tuning on AEM's, Motec's, ecu reflashing, and have done pretty much all the piggybacks, and have seen this happen way too much.