Bowtieman4life

iTrader: (1)

At what point do I need to move up?

CMNTMXR57

403rwhp here with stock injectors. In 98 they were 28lb/hr units.

Really, lb/hr isn't as important as the amount of duty cycle the injector works at at WOT. Once it starts getting over 80% duty cycle, it warms the fuel too much.

Team ZR-1

Cannot understand why people do not see that a stock injector on a modified engine would NOT be the best for performance when stock injectors are too small for even a stock engine such as a Z06.

If the simple known math is done,
assume a 28 lb injector:

28 * 2.04 = 57. 12 (HP per injector) * 8(injectors) = 456 FWHP (at 100% duty cycle) *.80 (80%) =365 FLyWheel HP.

So at 26 lbs = 339 FWHP with a 80% duty cycle.

Now those numbers may be OK for farting around crusing but for hauling around the high end of PE mode, they are too small, induce knock and lower WOT timing.

That hardly supports 400 Rear Wheel HP for best performance.

Also by having a larger injector allows a wider tuning window to solve ping/knock, use of smog gas, and low PE/WOT timing issues and the MPG increases since the PCM does not have to always go richer to solve the lean conditions so in long run PCM can shorten the injector pulse width overall and you gain MPG.

WICKED SS

iTrader: (36)

I have some for sale if your interested. 28lbs

Racehead

How can the above formula be accurate when I'm making 427 rwhp on the stock 28 lb injectors ? Assuming a 15% drivtrain loss that puts the duty cycle of my injectors at exactly %110, going by the above formula ? Atapped my car on the dyno, didn't actually check duty cycle, but timing,KR, and fuel mixtures were all ideal??

Team ZR-1

A dyno does not require the same amount of engine load as on the street, nor does it require injectors to be maxed out for more then maybe the last 10 seconds of maybe a 30 second pull.
A dyno pull only uses about 5 of the 23 fuel trim cells and thus does not have to deal with the effect of the other cells increasing leaner LTFT averages as it would in real world driving.


Nothing says an injector cannot run static at 100 % duty cycle, it just does not do it well over time.
That simple math has been used since injectors have been around and as an example the G.M C5R using 44 lb injectors ( I also use same injector and can get close to 80% when racing) , your RWHP is due to the NOS and as your N/A numbers show that is 100 HP less then with the NOS.
As to knock, you might have some type of PCM tuning and they have shut off knock functions.

Use a PCM scanner, drive hard (100% engine load) going up a hill and see what the duty cycle is.

jimmyblue

iTrader: (11)

The only thing that precludes running a bigger
injector (presuming you are going to tune for
it) is the PCM's low-pulse-width drive and the
injectors' low-pulse-width fidelity / matching.

I know some PWM ICs have trouble with minimum
pulse width "snapping" between zero and some
few-% minimum. This would potentially make for
rough running, surging, etc. if our PCM has a
similar low-end constraint and if you are
flirting with it.

With injectors, any discrepancies in actuation
time and narrow-pulse spray volume are going to
be more significant percentages of fuel delivery
as you run to lower pulse widths.

Thing is I've never seen any good info on what
a given injector species can be expected to do
in these respects, or what the PCM's minimum
good pulse width is (any deviations and
degradations aside, even).

I guess the best way to go is to figure up what
will get you to the magic 80% and live with
whatever happens down low (although maybe you
can find someone who knows the narrow-pulse-
width differences between the various injector
choices, or at least one choice that's no-prob).

Team ZR-1

You'll notice on a average the P.W GM has set to is about 3.xx mSecs.
Being the PCM is only a 16.7 Mhz CPU and all the extra bus and clock time for OBD-II and CAN data exchange the PCM has better control of injectors if PW is longer and reason I think GM used the injector size they did.

I have been using 44 lb injectors all this year and see via PCM scanning PW average about 2.5 and works OK but lower then that causes problems esp on decel where fuel trims go lean but overall with good PCM tuning methods the larger injector assures it is not the injector that is causing ill AFR when needing the most performance of powertrain yet idles just fine.

TomQ

ahh nuts

really hard to decide when you haven't seen at what duty cycle your inejctors are under different load conditions...

Vents

iTrader: (9)

John,

thanks for that good info, i learned.

99 Black Bird T/A

iTrader: (4)

So what does all this mean if you at 400+rwhp one should expect more rwhp and better performance with 30lbs injectors and a good tune?

felton316

Maybe, but I think its more peace of mind knowing that your're not pushing the stocker 110% waiting for it to fail. After seeing some of John's (Team ZR-1) scans, I also decided to go with the C5R injectors for my head/cam/bolt on's car. I'd rather have the ability to supply the extra fuel, if ever needed, then be pushing the stockers to full load at 6800 rpm's to find out they can't cut it.

JR2

MSCLCAR

The formula John used indicates I should be running 32lb injectors, since I dyno at 350rwhp (or 425fwhp). That seems pretty big for a stock motor with bolt-ons. And how much tuning is required? Can I get there with my Predator? And athwhat point do you need to change out the stock fuel pump?

By the way John, where is Team ZR1 located? The website doesn't say.....

Mark

TomQ

they are at Santa Clara, CA

Team ZR-1

Mark,
that is not really large, consider a stock ZR-1 Corvette has 16 injectors, each are 22 lbs, that comes out to 44 lbs per piston under load and that is for 405 FWHP.
Its not that the injector is flowing more fuel all the time, its only when the engine demand needs it, thus your assured under the worst engine load the injector will be be the delimiting factor.
Its a simple change via PCM tuning to change the injector flow table.
You not only get better performance, better gas mileage but the injectors are not been overworked with large pulse width on times.

In your case go with the SVO 30 injector, that gives you 36 lbs at a 80% duty cycle and this way with the HP you have the duty cycle will be below the 80% rule and if you add a few more mods the injectors will be able to support them.

The C5R injector which is like 44 lbs has been used on supercharged engines such as Grand National and SC380o cars.

Team ZR-1

There is no need to SEE the pulse width to make a choice on injector size, the simple math I listed above gives you a clear idea if you rather force your injector to be in a static state with high pulse widths or go with an injector that can flow more when required with shorter pulse widths which is less demanding on injector's coil and the PCM.

Consider if your using 26 lbs, a supercharger that only is adding another 100 HP starts with 42 lb injectors and I've seen some using 55 lbs so clearly a 36 lb injector would be fine for most modded engines until you get into the 450 RWHP range.

MSCLCAR

Thanks for all your help John,

By the SVO 30, I assume you mean the Ford injector? And I do not believe I can amke this simple PCM flow table adjustment with my Predator tuner. I am asking James @ RWTD now to see. If not, where are you located? Our only C5 / F-body shop up north closed a couple months ago. A bunch of us have been looking for a place to get custom tunes, etc.

Mark

99 Black Bird T/A

iTrader: (4)

Team ZR1,

Can you show us a dynograph from a ~400rwhp car where just the 26-28 lbs injectors were upgraded to SVO 30's or 36 lbs injectors and the tune tweaked for the new injectors? I like to see what difference it made on the dyno.

Thanks

Team ZR-1

Correct Mark the SVO 30 at our fuel pressure is like 39 lbs at 100% DC and 36 lbs using the 80% DC rule.

If as example your LTFTs have averaged 10% too lean,
and new injector could flow 30% more, minus the 10% lean equals the new injectors are about 20% too rich, thus you tune your injector flow table in PCM up by 20% and end up close to a zero LTFT average.
Then fine tune certain fuel trim cells that are still a bit lean.

I am in Ca, and if you have a PCM scanner and do some good recording wih all types of engine loads, and you sent me that and the PCM or a flash file via LS1edit I then can custom tune for the PCM recording data would allow me to tune as what the raw data is showing.
Without a decent PCM scanner recording then its a crap shoot and would be tuning in the blind.

Team ZR-1

Here is an example of a fairly stock C5 with some mods but with stock injectors and then changing to SVO 30 injectors.
Notice with stock injectors (bottom graph) lines have lean wiggle and then the top runs graph with the SVO 30s how smooth the lines are and the increase in HP and TQ



There was a 1 week lag between stock injectors dyno run and installing the SVO 30s and allowing PCM to recal out after the custom PCM tuning changes for the larger injectors and its dyno run.