romanc2003

Hi,
I have 1987 928S4. I installed 24lb ford injectors and an adjustable fuel pressure regulator. If anybody did this mod, could you let me know what is the fuel pressure for this mod?

Oh! Sharktoberfest was great!!!
it was good to see who is who because I always talk to them over the phone or web!

Thank you for all the people who made this great event!!!

John Speake

Hi
Find out at what fuel pressure your 24# injectors are rated at.

The relationship between fuel pressure and flow is a square root one, so doubling the fuel pressure changes the flow by sq root 2 or 1.4 times.

I believe the S4 injectors are rated at 36psi, but are run at 55psi, so you need to factor that in as well. In other words they are running at the equivalent of 44lb injectors at S4 fuel pressure.

You can do similar sums to work out the idle fuel pressure you will need for your 24lb units.



regards

dr bob

The orifice in the injector is not a smooth hole with square corners, so the flow prediction may not be exactly the square root of the DP. There is a large area where the flow may better be defined as choked, ....


Without getting into flow dynamics for 2-phase flows of liquids and vapors, gotta ask: Why did you change to the bigger injectors?

jpitman2

I thought LH ran at 2.5bar/37psi std for all implementations, and higher outputs were achieved with higher flow injectors, rather than unusual pressures.....?? No?
jp 83 Euro S AT 49k CIS

romanc2003

John,
Thank you for the info but You lost me....

dr bob,
Well, I have E-rams and modified exhausts. I was thinking bigger injectors give more HP. (find out I was wrong...) And in near future, I'm planning to install NOS or supercharger. So bigger injectors were kind of in process of supercharging or nos.

John Speake

Sorry, I made a complete mess of my mail - that will teach me to try and do calculations after a bottle of wine, late in the evening :-)

S4 injectors are of course rated at 19lb at 36/37 psi (thanks John P), which makes them effectively run like 23lb injectors.

So, find out what pressure your Ford injectors are rated at. If you let us know that, I will calculate what you should set the idle fuel pressure to..... when I'm sober :-)

Regards

romanc2003

John,
Here is info for my 24lb injector.

Injector Advertised Flow Rate (lbs/hr): 24
Injector Advertised Flow Rate (cc/min): 255
Quantity: Sold as a set of 8.
Injector Impedance: 14.5 ohms
Driver Type: 12V saturated circuit
Overall Height (in): 3.045
Seat to Seat Height (in): 2.563
Manifold O-Ring Outside Diameter (in): 0.545
Fuel Rail O-Ring Outside Diameter (in): 0.523
Outside Diameter (in): 0.982
Injector Plug Style: Bosch/Amp Style

For "19lb injectors". The fuel pressure should be at idle---47psi, without vacumme and engine running---55psi, right?

Thank you for all your help!!!

John Speake

Hmmm, tells us everything except the rated pressure for that flow rate...

I assume your injectors are FMS-M-9593-A302 ? I can't find the rated pressure, but their 30# ones are rated at 43psi. If we assume the 24lb are the same, then you need to adjust the idle fuel pressure to 35psi.

You are correct, static fuel pressure S4 is 55psi and idle is 47psi... I should have known better to reply on my memory. So that means the S4 injectors look like 22lb.

Bob had a good question, unless you are going for substanial power increases, why fit 24lb ? You could just use a RRFPR.

romanc2003

John,
Thank you for all your help!
If I can't install NOS, I probably go back to stock size injectors.

Thanks again to you all!

tv

What they said!!!! I think???

FlyingDog

So if there is a vacuum leak, the car will run rich?

dr bob

If there is a vacuum leak at the FPR, the car will run rich, since the FPR is fooled into thinking that the whole manifold pressure is higher.

If you have a leak where the only ill effect is bleeding air into the manifold, the car will hunt for correct mixture as it reads the oxy sensor reading and corrects for the lean condition. If too much air gets in, beyond the range where the brain can correct, the car will run lean, have a rough idle, and may stall especially after a trailing throttle run.

romanc2003

I found flow rates for ford and accel injectors:

Ford Motorsport 19.0lb/hr @ 39psi (Part no. FMS-M9593-C302)
Ford Motorsport 24.0lb/hr @ 39psi (Part no. FMS-M9593-A302)
Ford Motorsport 30.0lb/hr @ 39psi (Part no. FMS-M9593-B302)
Chevy LT1 24.0lb/hr @ 43.5psi (Part no. 17124248)
Chevy LT4 28.0lb/hr @ 43.5psi (Part no. 17124251)
Accel 19.2lb/hr @ 44.1psi (ACC-150119)
Accel 21.1lb/hr @ 44.1psi (ACC-150121)
Accel 24.4lb/hr @ 44.1psi (ACC-150124)
Accel 25.6lb/hr @ 44.1psi (ACC-150126)
Accel 29.4lb/hr @ 44.1psi (ACC-150130)

Imo000

Are you for real or is this someone just trolling around for fun ?

romanc2003

I posted flow rates for FYI.

I'm still in research stage for NOS....
But I'm getting answers like this: "NOS is for toy cars, not for the porsche..."
Well, this car is my toy....
Thanks