Bigger injectors?
Re: Bigger injectors? 80% is the general rule of thumb, if you stay under that, your probaly fine.
if you continually go over that, at wot, and high RPM's, its time to start looking into larger injectors.
Ryan
if you continually go over that, at wot, and high RPM's, its time to start looking into larger injectors.
Ryan
Re: Bigger injectors? I just ran into this problem myself. Looks like I may need to look into 30#'s after adding just a cam and headers.
https://ls1tech.com/threads/showflat...=7&fpart=1
https://ls1tech.com/threads/showflat...=7&fpart=1
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Joined: Nov 2001
Posts: 9,246
Likes: 3
From: Troy, AL
Re: Bigger injectors? I've learned to trust what's happening in the REAL world rather than in the world of not proven (and oftentimes disproven) calculation and theory. 
For street and drag racing purposes, stock 26.4 lb injectors are safe at 450 RWHP with an A4. (I made 480 with an A4 on slicks.)
For stock 28.6 lb injectors, make it 490 RWHP with an A4.
In M6 cars they'll go even higher due to less drivetrain losses.
In my '02 I have stock 28 lb injectors. I make 423 RWHP NA and I wouldn't be at all scared to run a 75 FWHP dry shot of nitrous on top of this.
***ALL FIGURES ARE ON A DYNOJET CHASSIS DYNO***
For street and drag racing purposes, stock 26.4 lb injectors are safe at 450 RWHP with an A4. (I made 480 with an A4 on slicks.)
For stock 28.6 lb injectors, make it 490 RWHP with an A4.
In M6 cars they'll go even higher due to less drivetrain losses.
In my '02 I have stock 28 lb injectors. I make 423 RWHP NA and I wouldn't be at all scared to run a 75 FWHP dry shot of nitrous on top of this.
***ALL FIGURES ARE ON A DYNOJET CHASSIS DYNO***
Re: Bigger injectors? Well, according to my O2's (I know they aren't the most accurate), My AFR is falling off at about 6100 RPM and has a slight dip right before I shift at 6400 where my injectors hit 95.5% duty cycle. I'd rather be safe and get bigger ones, but that's just me.
TECH Senior Member
Joined: Nov 2001
Posts: 9,246
Likes: 3
From: Troy, AL
Re: Bigger injectors? Gillbot, if you are truly out of fuel system capacity, then something is wrong. You're nowhere near what that system should be able to pull. If you adjust your WOT mixture richer from 6100+ with LS1Edit, what happens? If nothing happens then yes, you're maxed out. If it does in fact get richer, you obviously are not.
And, are we talking about a major change (like going from 12.8:1 to 13.8:1)? If you're using your car's O2 sensors for fuel/air then you really don't know the answer to this question. In fact, you could be running rich and not know it.
Is your fuel rail pressure still at least at 55 PSI at all times?
If not...
Pump bad?
Filter restriction?
It's not always the injector's fault when mixtures go lean. The pump in my '00 ran out of capacity before my injectors.
BTW, I do agree that it's always better to be safe than sorry. But you do have to ask yourself if what you are doing to correct a problem (and if you really have a problem at all) is really the right thing to do...as in going to bigger injectors when in actuality the problem is that the fuel pressure is dropping to 45 PSI at WOT, for example. In that case, the bigger injectors would be a bandaid at best.
And, are we talking about a major change (like going from 12.8:1 to 13.8:1)? If you're using your car's O2 sensors for fuel/air then you really don't know the answer to this question. In fact, you could be running rich and not know it.
Is your fuel rail pressure still at least at 55 PSI at all times?
If not...
Pump bad?
Filter restriction?
It's not always the injector's fault when mixtures go lean. The pump in my '00 ran out of capacity before my injectors.
BTW, I do agree that it's always better to be safe than sorry. But you do have to ask yourself if what you are doing to correct a problem (and if you really have a problem at all) is really the right thing to do...as in going to bigger injectors when in actuality the problem is that the fuel pressure is dropping to 45 PSI at WOT, for example. In that case, the bigger injectors would be a bandaid at best.
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TECH Senior Member
Joined: Nov 2001
Posts: 9,246
Likes: 3
From: Troy, AL
Re: Bigger injectors? Oh, and you are correct, your injectors are a VERY poor indicator of what your WOT mixture is actually doing. You might be very suprised to see what your mixture is actually doing if you get it on a wideband...I know I was! 
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Verdad Gallardo Re: Bigger injectors?
Gillbot, if you are truly out of fuel system capacity, then something is wrong. You're nowhere near what that system should be able to pull.
If you adjust your WOT mixture richer from 6100+ with LS1Edit, what happens? If nothing happens then yes, you're maxed out. If it does in fact get richer, you obviously are not.
And, are we talking about a major change (like going from 12.8:1 to 13.8:1)? If you're using your car's O2 sensors for fuel/air then you really don't know the answer to this question. In fact, you could be running rich and not know it.
And, are we talking about a major change (like going from 12.8:1 to 13.8:1)? If you're using your car's O2 sensors for fuel/air then you really don't know the answer to this question. In fact, you could be running rich and not know it.
I can't honestly answer how large the swings were since I don't have a wideband handy to tune with. I'm sure with wideband tweaking, the duty cycle may come under control but I'd rather have too much injector and run a little fat rather than go lean. 
