Wilson

SVO 24# @ 43.5 psi = 26.5#? How did you guys come out with this number? Some other board told me SVO 24# @ 43.5 = 25.8#.

Im confused on what my Injector flow rate (#/per hour) should be?

I currently run it at 25.8# Injector flow rate with 46 psi and im still showing a lean condtion in the BLM's. Im kind of afraid to go with 26.5#. Wouldnt this make my BLM's run leaner?

TRAXION

It was figured out by grabbing the appropriate formula out of an automotive book that deals with subjects like this. Plug the numbers into the formula and there ya go.

Tim

I8AStang

When I do the calculation I get approx 25.7. What you are looking for is the ratio diff the pressure makes in flowrate. It affects it as the square root of the actual ratio. When I do the math with ford fuel pressure of 39, and gm of 43.5 I get (43.5/39)^(1/2)=1.07. When you multiply this by 24 you get 25.7 . If you are seeing a lean condition, I definately wouldn't increase this to 26.5 . How much of a lean BLM are you seeing. The value people are quoting might be based on actual flow testin, instead of calculations though. One thing I noticed is you have made some changes that could affect VE of your combo. I would leave your injector constant where it is, and make small changes to you VE tables.

james_85Z28

since the only variable is the line pressure:

SQRT(43 PSI / 39 PSI) x (24 lbs/hr SVO) = 25.2 lbs/hr

this also works for those who have 30 lb/hr SVO injectors.

EDIT: doh! I forgot the square root

http://www.rceng.com/technical.htm

man tough crowd

a73camaro

BIG TIME!!!

New flow rate = Old flow rate * (New Pressure / Old Pressure)^0.5

or

New flow rate is equal to the Old flow rate times the square root of ratio of New pressure to Old pressure.

This comes from Bernoulli's equations regarding fluid flow where pressure energy, transitional energy, and gravitational energy are combined.

Transition energy has a velocity squared term (fluid flow), pressure energy relates linearly.

Take the square root of the above energies, and flow comes out linear and pressure varies as the square root.

Warlock

Ok, lets clear this up... a73 is right on with the formula and I8AStang is right, but goofed a number.

the 24# SVOs are rated at 39psi
so if you were running gm stock pressure (43.5), you would use a73's formula and come up with an injector constant of 25.35

However, you have stated that your pressure is 46. Using the same formula, your correct injector constant would be 26.07

With that said, if you are using a constant currently of 25.8 and all of you BLMs or the average of them are lean, increasing the constant to 26.07 will make it even leaner. Bad move.

Make sure you are not just looking at 1 BLM cell. If you are indeed averageing on the lean side, DECREASE the injector constant slowly to get you average closer to stoich, then fine tune your tables ignoring what the constant in a perfect world SHOULD be.

james_85Z28

I forgot the square root and have since updated my post

Grim Reaper

I've always heard 24# SVOs are rated at 38 psi.

86TpiTransAm

Personally I've seen 4 different numbers so far. Wilson says he read 25.8 somehwere, I8AStang is saying 25.7, james_85Z28 says 25.2, and Warlock says 25.35. Now Glenn is saying he heard that SVOs are rated at 38psi, not 39psi.

So many variations and it's no wonder people get confused easily.

Warlock

Go with my answer...

No idea who told wilson
I8AStang is wrong because Sqrt(43.5/39)= 1.056117709 not 1.07
James rounded his Sqrt before multiplying by 24 so he is close, but not quite right
And while I would normally defer to Glenn on most subjects and doubt I will ever know this stuff as well as he does, he has simply heard wrong in this case.

Wilson

Stock GM fuel pressure is measure by removing the vaccum line on the AFPR right? Then you set the AFPR at 43.5 right? Im going to back down my fuel pressure to 43.5 tonite and use Warlocks injector constant of 25.35. I'll let you know how that goes. I'll post some data logs in csv form tonite. :lala:

86TpiTransAm

Yes.

I8AStang

The general consenses is it is the ratio of the square root of the pressure changes. this does in fact come from the Bournoulli equation. The difference in everyones numbers seem to come from differences everyone is using as their pressures. Is it 38, 39, 43,44,45, 43.5 etc..... I'm fairly sure I can't measure and set pressure to closer than 1psi, and production line variation is at least that great(the spec I have in a shop manual is a 4psi range I believe). People aren't wrong because there mulitipliers ar .02 off. To anwer the guys original question, if it is already lean do not increase this number, math shows it should be between 25 and 26.

Craig Moates

Bernoulli...sort of. Just think of the fuel injector as a valve with a particular Cv constant which describes its resistance to flow.

No one's getting sonic flow here, no real phase changes, and flow is incompressible (liquid), so it's easier. The flow-pressure correlation should follow the square root relation directly. We use this all the time at work to calculate flows through orifices & what-not. Just adjust the flow at one pressure to the flow at some other pressure. It's just an orifice of variable opening duration after all.

Warlock

In case you want to be lazy...use the calculators here:

http://www.rbracing-rsr.com/fuelinjectors.htm