I've been searching quite a bit on the boards lately, trying to find a decent answer regarding what a good fuel pressure setting would be for a stock L98 setup and some 24# SVO injectors. Even better would be a general formula or ratio for what the SVO injectors flow given a certain fuel pressure. So far all I've found are some general wishy washy answers that don't really come to any conclusion. Numbers from 37 to 46 have been thrown out there, and I've heard one person say some SVO injector at TPI fuel pressures will flow like a Bosch 26# injector will. I can't remember the specific rating that was for. Anyway, I know that I need to reprogram my PROM for the new injectors for them to really fix this issue, but until then I wanted to band-aid it by dropping my pressure. I was thinking that 30 to 35 PSI was a decent range from the generalities I've gathered, so that's where I'll start the "bidding." Anyone have some other input from close experience with the same issue?

 

new flow/old flow = sqrt( (new pressure)^2/(old pressure)^2)

simple as that. Off the top of my head i don't rememeber what SVOs are rated at, definitely either 39.5 or 37.5 psi. GM is rated at 43.5.

 

Why not just try running the pressure up and down and find out what works best for your car? IM not trying to be a jerk... just seems like the best way to do it.

 

Maybe even burn a PROM to properly compensate for the new injectors flow rate at the stock pressure!

 

Ed,

Your equation is correct if you do not include the 2s.

Squaring the numerator and squaring the denumenator, then taking the square root of the whole thing is same as doing nothing.

New fuel flow rate = sqrt(new pres/old pres) * old fuel flow rate

I believe that what I have above is correct.

 

If they are rated at 39.5psi then you should start at about 34psi to get 22#/hr, if they are rated at 43.5 psi then you should start at 37psi.

 

oops. Figures i'd flake just trying to recall something like that. It did seem a little funny, lol

 

Thanks for the help guys. I think I'll just set it at about 35PSI and see how that goes for starters. And I am planning on burning my own PROM for it, but I just don't have the equipment or software for it yet, and don't have the money for it yet, so this is just an easy fix until I can work it better.

 

This is probably no help but, here it is anyway.
http://users.erols.com/srweiss/tableifc.htm

 

no ford and chevy injectors as well as doge and some other "bosch style" are all rated at the same PSI. If there is any difference it would be like going from 22# GM to 24# ford, but that is just the difference between 22# and 24# not the difference between ford and GM. see this post on the subject. https://www.thirdgen.org/techbb2/sho...hreadid=120342

 

Not to be an a$$, and not to say you are wrong or right, but where did you get the information on this subject that led you to your conclusions?

 

I got it straight from the flow bench man

 

IROCSS I believe said the same thing. He saw on a flow bench that they all flow the same. Apparently the standard pressure for testing is 3 Bar which is 43.5psi

 

yeah thats it just like in my link its the SAE standard.

 

Hmmn, interesting. I had some email conversation with Rich at cruzin performance.

The info I gleaned was Ford injectors are rated at 36.5psi??, and GM at 43.5psi.

Rich is "The Man", IMO.

Regardless of SAE spec's, that's only useful to compare things equally...i/e I've seen new injectors for GM cars, new injectors for Ford cars, and new Accel injectors (all in the box) and nothing came with them specifying the rated flow was at any industry standard.

That said, only real way to know would be to measure flow on the FMS injectors and GM injectors at the same SAE Standard, and compare the results.

Doeas anyone know who has done this?

 

I know you guys all love him but what I saw is what I saw and what I saw was a a couple of 19# chevy a couple of 19# ford and a couple of 19# dodge injectors all on the flow rig they were all untouched (just clean) and flowed within a few grams per second of each other. and all were flowing 19# at the same rail pressure.

 

So, if what you are saying is true, then there are several hundred people on this forum alone that have installed the SVO injectors and after doing so have had to lower their fuel pressure or change their injector constant so they didn't run too rich and by your information they shouldn't have had to. I'm sorry, but I don't buy it. There are way too many people with real world experiences that prove that the injectors flow at different rates.

 

My injector constant for my 30# SVO injectors fell at 33.5#/hr when I got the BLM's reading like they used to.

 

Tough ****, Im not asking for your approval and if this is so then howcome aftermarket manufacturers dont list a different 19# for chevs and fords? see I can find lame evidence too. Its as lame an analogy as racing your buddies 12 second car and winning then claiming yours is a 12 second ride. I have seen people put in totally stock replacement injectors that had to fool with the FPR does that mean stock GM injectors flow differently too?

 

You don't have to take what he is saying personally, the guy is just skeptical. And from what he is seeing, he is finding it hard to believe the info you are putting out.

If you were to have, like say.... annotated pictures or printouts to back up what you claim, it would be a lot easier to understand and have faith in. But earlier you stated that they are all rated with the same rail pressure, but you didn't know the ambient rail pressure that is the actual standard. Things like that foster doubt. I truthfully don't know for sure if you are correct either and as much as I believe you are a competent individual and a man of your word from previous conversations with you, there are waaaayyy too many self-proclaimed experts on the net these days and it behooves oneself to be skeptical . Raw data would do wonders for the doubtful .

I have the 30# SVOs on my 355 right now and did the math for a 43.5psi GM rail pressure and a 39.5psi rail pressure for the FMS injectors to come up with 33# for my injector constant. I then proceeded to fine tune the rest of the calibration from there and my engine combination isn't all that stock so it is difficult to say if that converted injector constant is appropriate or not. But I can say that I didn't have to make whole-sale changes to the VE tables in principle, so maybe that figure is pretty close.... But the numbers are close and there are plenty of other variables, so I really don't have anything concrete enough to weigh in on this with any kind of confidence .........