Should I get larger injectors?

Hoytster

I don't dare do that to my Knob
Dirt-Old 20+Year Member
Dec 30, 2002
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Cornwall, PA
I got my Tweecer in the mail yesterday, got it installed and started down the road to do some data logging.

I was surprised to see my 24lb injectors were pegging past 100% around 5400 RPMS. Does this mean I should get a bigger injector, or can other factors skew this reading? I want to start tuning the car but I know it will be counter-productive if I need to go to a bigger injector.

My combo is listed in my sig.
 
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I highly recommend bigger injectors. Most HCI combos should be injectored to 30 pounds anyway, IMO.

A lot of guys get away with an adjustable fuel pressure regulator as a band-aid, but that is not the "right" way to do things. The 24 pound level is an easy way out because the stock cobra tune is setup for 24s... loading that cal and working from it is fairly simple.

If you have the patience to hammer out a tune with the TwEECer, then skip the 24s and go to 30 pounders.

Hell, I'm strapping on a 125 shot soon, and even with my grocery-getter stang I think 30s are correct. The propensity to ping, STOCK, in our cars should be considered when you're on the fence. Besides, 30s will also allow some breathing room in case you decide to upgrade to a hotter cam / track heat type combo.

Adam
 
With aftermarket heads, cam, intake, and all the supporting stuff

and

when talking about a na combo.

I've always believed 24's are right at the limit :(

or

in some cases, 24's are too small :eek:

Keep in mind, I'm talking about using stock fuel pressure here :)

I base that belief from using many of those inj size formulas you find out there

and

from talking to many other self tuners in the past year or so and hearing some of their experiences when using 24's.

Its the amount of airflow that dictates the size of inj one should choose :nice:

I wanna make it clear we are talking about more airflow than a typical bolt on combo. Something around 300rwhp or better.

Sidenote +++ recently Don 95Vert posted Ford uses fuel pressure that is a couple of pounds less than our inj's are rated for. That means you are not getting the all of the inj rating no matter what size inj you run if you use stock pressure :eek:

Another thing for Tweecer users :D

Once upon a time ... the inj duty cycle was known to be off

or

It was a bug in the Tweecer software.

Don't know if V1.30 had the fix or not.

For me ... I don't need no software to tell me what my caculator has told me

and

other peeps have told me about 24's.

See my sig and you'll see I practice what I preach :rlaugh:

I'm not telling you to move to 24's as you already have them :nono:

Maybe you should run 3 to 4 pounds more pressure as your permanent default fuel pressure setting before you get started on your tune :shrug:

Thoughts from other members about this as a solution for 95Black50 :shrug: :shrug: :shrug:

Grady
 
I'm not against spending a couple hundred bucks to move up to 30's if it's going to make a more "stable" combo. Since I had the 24's stock I had just thought I could get away with them.

When I was planning this combo I had set a goal that I would not skimp on any details that would affect the power, driveability, and longevity of the vehicle. I'm not the kind of person that likes to drive components to and past the edge. I would rather see an injector duty cycle at or below 80% at max RPM so I know I have a little more breathing room if things go wrong.

Looking at everyone else's combo's it seems that I might have better success running with the 30's with the type of combo I'm running.

Maybe a few pounds of fuel pressure would help my 24's support my combo, but if they're pegging past 100% at 5400 it makes it hard to beleive a few pounds would bring the duty cycle down to a level that I'm comforable at running at 5800-6000 RPM.

Final5-0, your comments and suggestions have been appreciated throughout my project. You bring up some very good points, and seeing that your combo uses 30's (with great success) pushes me toward that side of the desicion even more.

I'm going to be running at the track for the first time tommorow, and of course I'll be logging. I want to get a baseline of how she performs before, and then after the tune. Maybe I can post the logs and see if that can help shed more light on this problem. I've only had this tweecer for 2 days now and I know I don't have a handle on the whole datalogging thing like many other members on this site do.
 
95Black50 said:
I'm not against spending a couple hundred bucks to move up to 30's if it's going to make a more "stable" combo. Since I had the 24's stock I had just thought I could get away with them.

When I was planning this combo I had set a goal that I would not skimp on any details that would affect the power, driveability, and longevity of the vehicle. I'm not the kind of person that likes to drive components to and past the edge. I would rather see an injector duty cycle at or below 80% at max RPM so I know I have a little more breathing room if things go wrong.

Looking at everyone else's combo's it seems that I might have better success running with the 30's with the type of combo I'm running.

Maybe a few pounds of fuel pressure would help my 24's support my combo, but if they're pegging past 100% at 5400 it makes it hard to beleive a few pounds would bring the duty cycle down to a level that I'm comforable at running at 5800-6000 RPM.

Final5-0, your comments and suggestions have been appreciated throughout my project. You bring up some very good points, and seeing that your combo uses 30's (with great success) pushes me toward that side of the desicion even more.

I'm going to be running at the track for the first time tommorow, and of course I'll be logging. I want to get a baseline of how she performs before, and then after the tune. Maybe I can post the logs and see if that can help shed more light on this problem. I've only had this tweecer for 2 days now and I know I don't have a handle on the whole datalogging thing like many other members on this site do.

Thank you for the kind words Chris :)

Since you be a noob tweec geek, lemme give you a thing or two to think about ... OK :D

The move to 30's will take you a while to get everything dialed in just right but at your power level... I do think its a wise move :nice:

Here are a few things to start your research on that will help you.

Lets talk about your C&L maf :)

With you being just two days old, (in Tweecer age that is) I'd be willing to bet you are using your maf in cheat mode.

First thing you'll need to do is load in the transfer curve for your C&L ... if no other C&L users fill you in here, you can get the details at the Tweecer site as there are a lot of C&L users there.

Now lets talk about those 30's :)

Use the following items to load in 30lb values

low slope - scalar
high slope - scalar
inj offset vs batt voltage - function
breakpoint - scalar

EEC Analyzer can help you tremendously with the above items :nice:

That should be plenty to get you started when you decide to work with the 30's and your C&L curve ;)

Again ... I'm not all that sure the inj duty cycle you see in your dlogs can be trusted. Search around on the Tweecer site to confirm unless one of the other members can verify my concern here is valid or I'm romin around way out there in left field :rlaugh:

You know what Chris? ... It just came to me :banana:

You could always juice up the pressure by about say 6 pounds and see if the duty cycle goes down :shrug:

Then again, if it ain't accurate, how is that gonna help :scratch:

Sorry for the senior moment :chair: I'd better press on :D

We have gotten quite a few self tuners here so be sure to search around a bit for some excellent research.

I got a little bit of stuff on my site as well that could help I reckon.

Good Luck at the track tomorrow Chris :nice:

Since its your first time ... hope you have lots of fun :banana:

Grady