Fuel Injector Experts

[lucheski]

How much fuel pressure can I reliably run through a fuel injector?
One place said less than 100psi another said 65psi another said 80psi
I want to hold off buying #24s and run #19s at high pressure

Do I NEED #24s for this
Here is my combination

Sterling Hypereutectic Pistons
Port and polished Lower Intake
1969 351W Heads (30 hours of hand porting)
60cc combustion chambers machined to 50cc
10.5:1 Compression Ratio
Ford Racing F-303 Cam
1.84/1.54 Valves
Harland Sharp 1.6 Roller Rockers
A9L Mass Air Computer
70MM Cobra Mass Air Flow Sensor for #19s
Port and polished Lower Intake
Chromed Cold Air Intake Kit
Custom H-Pipe with Flowmasters

[1989GT]

Anything above 80 PSI and you risk the injector sticking open. I would say that you're fine with 19's but you could use 24's with closer to stock fuel pressure. You'll be fine either way. Are you running a stock ported intake? Also I thought the cobra MAF was "calibrated" for 24lbs injectors.

[lucheski]

Thanks for the info, I took a minute to study your profile, how much pressure are you running in your combination?

I know what you mean about the cobra maf. I bought that cobra MAF on ebay, the seller has cobra mafs for #19s on there all the time. But mine hasnt arrived yet, so we'll see how it works.

[tmoss]

Anytime you have to run over 44psi (3 bar) on an injector to get a good air/fuel ratio, it's time to move up to the next size injector. The Bosch Design II "pintel" style injector that came stock on our cars flows about 20-21# @ 44psi, and the Bosch Design III "disc" type injector like came on newer SUV cars like the Explorer flow 21-23# @ 44psi.

[1989GT]

I'm running 53 PSI on the stock injectors. I'm getting ready to upgrade to 24's though. Just haven't put them in yet. Of course I'm porting my heads right now so I figure I'll need the 24's by the time I'm done. Also I don't agree with tmoss' statement, injectors need a certain amount of pressure to produce the spray pattern they were designed to produce. So if you up the injector size too soon you'll run too low of a pressure and get a poor spray pattern. But also the EEC determines injector pulse width so say I'm running 40 psi with my current combo the EEC would take readings from the MAF, O2's and others to determine the pulse width, running 53psi just makes the pulse width shorter or closer to stock which makes it easier for the EEC to adapt to. So really if you wanted you could leave your fuel pressure stock and be fine... of course there are limitations as to what the EEC can adapt to. But like I said you're fine with 19's but you'll be fine with 24's too.
-Ryan

[tmoss]

Originally posted by 1989GT
Also I don't agree with tmoss' statement, injectors need a certain amount of pressure to produce the spray pattern they were designed to produce. So if you up the injector size too soon you'll run too low of a pressure and get a poor spray pattern. Ryan

Any basis for your statement? Bosch injectors produce a good enough pattern for good atomizing as low as 30-32psi if the injector is clean and were only DESIGNED to be used to 44psi.

Yes, you can run more but what affect does that have on the magnetic circuit that lifts the pintel? It makes it lift later (and possibly not a high depending on fuel pressure) and it closes sooner as it has to overcome more pressure to open and has more pressure assisting in closing it - the injector was not DESIGNED to run at that high a pressure. F/S guys run 100% duty cycle at high pressures to feed their 340-350 "stock" engines with 19# injectors, but they only do it 1/4 mile at a time - they are not street engines.