Fuel Pressure Question..42lb Injs

[eades5.0]

I have been running my 42s for quite some time with my base fp @39psi. After some research I'm reading that guys are sayin 42's dont spray correctly till like 42-44psi...how true is this?
I've had zero probs, but would like to know for the record.

Also what is the max fp you'd recc. me running. If I do go lean on the dyno, I will turn the fp up...whats the max you guys recc. like 50psi?
I know this would be a bandaide, but would hold me over untill I do a fuel system.

Thanks
Chris

[blown1989saleen]

with your 331 and boost, I can tell you right now your gonna max them with 39-40psi base fuel pressure, once up around 500rwhp the 42s need a bunch of base fuel pressure to keep up. Id start with 50psi and see what the A/F and duty cycle looks like.

[eades5.0]

Thanks man, exact kinda info I'm looking for.

At 50psi does the spray pattern get fuzzy?

[blown1989saleen]

Thanks man, exact kinda info I'm looking for.

At 50psi does the spray pattern get fuzzy?

no the spray pattern will be excellent at 50psi, its the lower pressures (below 36psi) that the pattern is not so good.

[eades5.0]

Thanks

[fanglemeister]

If these are the lime-green Bosch 42s then they aren't really shooting a true 42 pounds per hour at stock Ford fuel pressure -- they are a true 39.5 #/hr injector when being supplied at Ford's stock FP of 39psi. You have to run them bumped up a bit to get 42 #/hr, Bosch rates them for 42#/hr at 43.5 psi fuel pressure.

The ideal spray pattern is right at this fuel pressure, but there's a fairly reasonable pressure range, from @ 36 or so up to 70-75 psi, that they will spray (atomize) fairly decently. Any more than that and you risk them locking up, &/or overheating the injector driver circuitry in the eec.

Here's an online calculator to tell you what the new fuel flow should be at various pressures. Always enter 43.5 psi when entering the manufacturer's (original) flow rating.

http://www.smokemup.com/auto_math/fu...ure_change.php

I strongly recommend a custom tune when running big injectors, this will fix alot of driveability issues blamed on bigger injectors, and you'll end up making much better power than plain old fuel-pressure-only tuning. If you are dyno tuning to get close close to the ragged edge for track use, make sure you clear the eec memory before dyno tuning, to start with a known (+0% eec fuel trim) fueling baseline.

[BLOWNBY]

FWIW

I had 42's with a base FP of 34#. I also had an FMU. I made just over 500 rwhp and had no issues for 3 years.

[indy2000]

There is no need to adjust FP unless your running inj.s designed to flow at a specified (different) pressure. You must maitain this specified pressure, hence the regulator with a port.

If your running Ford spec (or comparible) injectors the stock regulator is all you need.

This is not apllicable if your force open loop.