i have a question. our ecu does it control the injector output(duty cycle) to compensate for rich and lean conditions? Is this how it puts more or less fuel into the engine? and if so, is there an ideal size of injector to use to minimize the duty cycle our injectors see and also minimize fuel pressure. for example...can we use a steady 30 psi with say 370 cc injectors to run our turbo cars without a boost dependant fuel pressure riser and just an idle fuel pressure regulator. i just don't like running 110 psi of fuel pressure, man that is alot, even if it is just for a short time.
thanks
lates
james

I'm sure there is. Our ECU can control +/- 25% duty cycle to compensate for a rich/lean condition. If you lower the static fuel pressure to say 30PSI, you may be able to run a 310cc/min injector with no electronic help.

(235cc * 25% = 298cc/min)

>i have a question. our ecu does it control the injector
>output(duty cycle) to compensate for rich and lean
>conditions? Is this how it puts more or less fuel into the
>engine?

Yes, the ECU changes injector duty cycle to adjust fuel. Bigger injectors let you spray the same amount of fuel in less time (lower DC). Assuming that the stockers have to run at 100% DC, you would want to choose a new injector to spray the same fuel at less than 85% DC. Go with too big of an injector and you will run into problems with inaccurate control at low fuel flow conditions (idle, cruise).

and if so, is there an ideal size of injector to use
>to minimize the duty cycle our injectors see and also
>minimize fuel pressure. for example...can we use a steady
>30 psi with say 370 cc injectors to run our turbo cars
>without a boost dependant fuel pressure riser and just an
>idle fuel pressure regulator.

You still must use a 1:1 regulator at least. Remember that the amount of fuel sprayed in has to do with the pressure across the injector. That is fuel pressure minus manifold pressure. So in order to supply a constant amount of fuel, you must match every Psi of boost with one Psi of fuel. I still recommend using greater than a 1:1 ratio (2:1, 3:1...). This takes some of the load off of your S-AFC. I had nasty bogging problems when I tried to run a straigh 32 psi fuel pressure, just using the S-AFC to adjust fuel with boost. Putting in the 2:1 disk helped so much.

> just don't like running 110
>psi of fuel pressure, man that is alot, even if it is just
>for a short time.

You can easily keep your fuel pressures down to a more sane level with some bigger injectors (60 psi seems way more sensible doesn't it). I'm seriously making a VFAQ that will help you definitively answer your questions...I need a few more days though. You'll be able to calculate all the numbers you'll need.

Corbin

'95 ESI-T
HRC+FMIC+ETC...

Corbin.. it's in demand.. hook up the VFAQ. I need to picture the figures. I got desperate.. and sold the DFI to a guy in my crew for only 500 w/ calmap. I have stock injectors in my ride right now.. the 450cc's are long gone.. sold the AFC.. still have the 12:1 regulator.. so basically I'm starting over.

You're in luck I spent 8 hrs today finishing it up, uploading, and altering my site layout (and many more hours before that). It takes so long because I'm always revising the text and pictures to be easy to understand. I'm not going to make any more VFAQs for a long time :). Lemme know if anything doesn't make sense.

Technical information page:
http://www.geocities.com/vttalon/tech.html

Installation page:
http://www.geocities.com/vttalon/install.html

Corbin

'95 ESI-T
HRC+FMIC+ETC...

I really have some work in front of me reading all of that.

I wish you had a similar VFAQ for a good tuning method you recommend as well. (am I demanding or what?!?! ;-) ) I've heard of different methods including using your EGT and a/f meter as well as using datalogging methods through the use of timing.

Either way, thanks for all the work! I've spent like the last 1/2 hour reading all of it, and I know I'll have to read it several times to get a grip on all of it! Terrific job! :-)

Yes indeed. I have my work cut out for me to calculate if my fuel system is up to par now....

Thanks

Well, after playing with those numbers this afternoon, I've quickly noticed why the use of FPR's becomes somewhat less effective for 300+HP.

Even trying to keep your injectors at a more reasonable size(not so large that idle becomes impossible), I find that HP at the 300+HP level requires big ole 550's at least. And that's if you don't mind pushing fuel pressure of about ~80psi's or so.

I guess if you were shooting for ~300 HP(at the crank) which is probably something like ~15 psi in a large turbo, you could push the 440's to their limit, but you'd be using fuel pressures close to 100psi. Not to mention, your fuel pump(s) BETTER be up to the task.

Moreover, for any of you guys _just_ using ONE walbro fuel pump on stock injectors, boosting 7-8+ psi, chances are more than likely you're probably going a little lean.

This formula usage is great for goal planning. There's certainly little reason in my mind to getting injectors any larger than 370cc's or so if you plan on staying less than 10 psi or so. Moreover, if you upgrade your internals and want to push some serious (300+HP), get some 550's or even 625's or maybe even some 700's if you want to get some crazy times.

Now only if we can find some cheaper methods to control these big ole injectors off boost. Stand alone ECU's are $$$. It seems a lot of companies are devising ecu help to control big injectors. Hopefully somthing can be worked out for us, since I've noticed most of the companies are making these products for Hondas.

It's certainly a challenge for turbo kit owners to stay out of the dangerously lean world. Between small injectors with one fuel pump and a fuel mapper that clamps voltages way too low, it's amazing there aren't more of us blown up! :-(

(thanks for the info again Corbin...it's any eye opener)