bufmatmuslepants

iTrader: (3)

Has anyone tried running 60psi instead of 43.5 instead of getting 30 lb injectors for example? Stock injectors are about 28s when running 60psi, has anyone gone that route who was on the brink of stock injector limit? I'm guessing my new motor will make between 375 and 400rwhp, which is on the brink, and I am debating the advantages of 60psi atomization vs 30s on stock pressure.

SS RRR

iTrader: (2)

I thought the PCM countered any fuel pressure adjustment if it is above stock pressure?

Catmaigne

iTrader: (6)

The PCM has no idea what fuel pressure you have, it just assumes 43.5 psi and stock regulator.

I honestly wouldn't. The stock multec injectors have a crappy spray pattern to begin with and upping the pressure might make it worse. Bosch III's are pretty cheap and widely available. I've been using the white 36# GTPs for years.

Shownomercy

iTrader: (1)

Base ~55psi here.

SS RRR

iTrader: (2)

I don't remember where I read that from. Probably the same ones who said it was a good idea to put a resistor in the air temp sensor for more fuel because more fuel is more powerz...

ACE1252

The PCM will counter the higher pressure with the fuel trims unless you account for the fuel pressure change by changing the fuel injector flow rating in the PCM.

For example, the Ford injectors I run are 30lb at 39.15psi. However since our pressure is 43.5psi, that puts the fuel injector flow rating actually at 31.68lb(if I recall properly).

The kicker to getting the injectors working properly is having accurate fuel injector characterization data. Ford Motorsports is the only OEM, that I know of, that puts out that data with their injectors.

You can get the steady state flow numbers calculated...but the short pulse adders and injector offsets are nothing but guesswork without that characterization data.

Catmaigne

iTrader: (6)

Well yeah, you'd have to adjust the injector constant any time you're flowing more fuel than stock, regardless of base pressure.

Another problem I see with upping the base pressure on stock injectors is that the regulators are not constant, they vary with manifold pressure. Swapping regulators and changing the base pressure dramatically could require more involved idle and part throttle tuning which just seems like a pain in the ***.

You can get all of the injector data for the Bosch GTP injectors (0280155811 and 0280155737, avoid fakes) because they were used in plenty of supercharged 3800s and ASA Corvettes. The data is out there in those stock tunes and has been posted across the web, but I honestly feel like they run better with stock LT1 offset and pulse width tables.

Catmaigne

iTrader: (6)

Other options are the Bosch red tops aka Ford SVO 30s. They can be had off of some turbo Saabs in the junkyard.

ACE1252

My trims were skewed badly with the stock short pulse adders and offsets. Once I got the calculated values in based off the Ford data things started looking much better. The windows version of Autotap had me chasing my backside for a while. LTFT on bank 2 is not reported correctly. The old DOS version seems to report okay.

I have not compared it to my Tech 1 though. I need to do that to see how accurate it really is...

Shownomercy

iTrader: (1)

LS1s run higher base fuel pressure than old LT1s and with 1:1 regulators just fine. Not sure why you can't do the same with an old LT1.

Is it a simple matter of cranking pressure and hoping for the best? No. But this is not nearly as challenging as its being made out to be here..

AgFormula02

iTrader: (13)

couple points:
f-body LS1s run a constant fuel pressure. There is no change to pressure based on manifold vacuum in the stock system.
The stock ls1 tune has different injector flow rates vs manifold vac because rail pressure is constant but manifold pressure changes, and final flow is based on differential.

Back to LT1 world:
Yes you can bump up fuel pressure some.
It will help better atomize fuel.
You should be able to go up to 50-52 psi and be OK.
If you do not tune for it:
-you will be rich at open loop and wot
- you will be OK at closed loop but l-trims will be skewed.
Gas mileage will suffer and you risk cylinder wash down if you get too crazy with pressure.

bufmatmuslepants

iTrader: (3)

All of this was assuming adjusting the injector flow rate constant properly in the PCM, so it's literally the same as if you put in 30s on base pressure and put 30 in the injector flow rate, but using 28.18 on 60psi instead.

This may not be what I do, more than likely I'll get some other injectors like Catmainge suggested, just seeing if anyone has done it.

cardo0

Yea, I needed higher pressure after may cam change but had a local tuner do with the dyno for tuning. Can't recall but it's North of 50psi. Tuner is familiar with LT1's and TunerCats program but I don't know how much he changed the injector constants - like normally done. We did have to put a better fuel pump to make that press.

What I'm saying it's not a big deal if you know what you're doing. But a trap if you try looking at FORD injector constants to tune a Chevy!

SS RRR

iTrader: (2)

And to think you could have used stock injectors at stock fuel pressure with a stock pump and everything would have been just fine...

BALLSS

like some of us on this forum I have been wrenching/modifying my LT1 for about 20 years and like many have H/C, etc requiring larger than stock injectors. All of course require a PCM adjustment. One thing my tuner said "make sure your FP is 43.5 lbs" so "his tune" would be correct for the 30 lb Ford red top injectors. He said raising FP to get the larger injectors to work is not the way to do it.

yeah there are other ways to skin that cat but from everything I have learned and read over 20 years about the LT1, keep the FP stock. If for some reason a stock (non adjustable) FPR does not get you 43.5 (say 41ish which is still within range for stock injectors) your tuner may advise a adjustable FPR so you can set it dead nuts on 43.5 which is optimum for his tune with larger injector modifications in the PCM

Yeah there are more exotic or track only builds that go outside of those lines....but I don't think this thread is about one of those builds.

ACE1252

I don't think there is anything wrong with bumping up the pressure as long as you get the all the injector data right. That is the part that can bite you...which is why so many say just get bigger injectors. Even then, injector data is a concern.

The other thing might be reliable fuel pressure regulators. I've read over the years of several brands not working right.

If I recall, NoMercy corrected me on the ZR1's fuel system. I assumed it was single pressure, but it's a dual pressure system.

ACE1252

Cardo0, as usual, you have NO earthly idea what you're talking about when it comes to LT1 PCM tuning.

Your logic is like saying an LS swap into a Mustang will not allow the car to run down the street. I assure you, it sure as *%$! will go down the street if you know what you are doing.

Don't know why I even bother feeding this troll....

cardo0

I just drove my car again and it's running great while it doesn't use any FORD injector data . Something a flake would use to tune a Chevy would be data from the wrong injectors and try and tell others they need stupid data. Something a real flake would do.. Just as he has to tell everyone he has a degree otherwise no one else would be able to realize that from his BS. More like he's a flake and a half as he has to wear his credentials on his sleeves hoping someone believes him.

ACE1252

The truth hits a little too close to home doesn't it big guy? Apparently so with that mouth full.

You'd do well to listen to this advice....best to keep your mouth shut and let people think you're stupid rather than open your mouth and prove it.

As far as the mention of my degree in my sig....worked 40+ hour weeks full time while taking night classes and adjunct teaching PLC programming/Home electric power classes to get that degree. Lots of work went into it. So yeah, I'm proud of it and display it.

I have two more degrees that I don't display. However, I'll strongly consider displaying them just for you buddy.

muddyjimmy

iTrader: (15)

I run 24lbs Bosch III injectors @ 60 psi on my heads & cam LT1. With proper tuning it works just fine.