How Much Fuel Pressure?

Jake

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I have mine at 55 psi. I have run it up to 70 and can't tell the difference. I figured my fuel pump will last longer at 55 psi
 

big_stroker

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I keep mine at 64. All trucks and setups are different. You probably just need to adjust it and see how it drives and adjust it again and see what your truck likes best.
 

CSIPSD

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Every truck, every injector is different...

With stock injectors I ran 70 psi, with stage 1-2's I ran 72psi... With the hybrids they seem happiest around 62 psi.
 

TARM

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Has anyone noticed a correlation between going to larger nozzles and higher fuel pressure? Thinking what we are really after is flow to refill the injector in enough time. As you go to larger nozzles you are able to empty faster and at higher rpms. This would seem to necessitate fast refill times and thus more flow so more pressure in this setup.

Where 60psi would be fine for max runs with 100% 65 would be better for a 200% and with a 400% 70psi would make sense? This is of course beyound what the SOTP and sound eval might find works best outside this.
 
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ITUKMOR

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Fuel pressure is more important to the life of the nozzle than to power loss. Think about how hard that nozzle needle hits it's seat. When fuel pressure is down there is less cushion. This can cause nozzles to lose flow over time, and in the case of larger nozzles (200%, 400%, & 600%) to crack/break. We have tested fuel pressures from 50psi-90psi and found that 65-75psi is optimum. After 75psi is there is no positive gain. The OBS trucks seem to do fine with 160-170cc injectors or less with the mechanical pump and lower pressures. However any split shot truck or truck running hybrids should try to keep the fuel pressure > 60psi. This is our policy when it comes to injector warranty.
 

Gearhead

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Does anybody actually know how the fuel injectors actually work on this thing? If you put too much pressure, you can actually force fuel under intensifier piston and slow the injector. You just need to keep the injectors filled and nothing more. I recommend somewhere between 55 and 62.
 

ITUKMOR

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yeah, we have built a few sets (2400).

I think we have a general understanding at least
 
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golfer

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Does anybody actually know how the fuel injectors actually work on this thing? If you put too much pressure, you can actually force fuel under intensifier piston and slow the injector. You just need to keep the injectors filled and nothing more. I recommend somewhere between 55 and 62.

Matt..the higher the rpm..the more pressure required.

that's why (we believe) none of the AirDog, FASS systems work worth a chit on the 7.3's or 6.0L's...since they are high VOLUME but low-ish PRESSURE.

these systems work great on CR trucks, VP trucks, VE trucks...anything WITH an injection pump...since the injection pump merely has to remain PRIMED with fuel...and those style injectors don't "refill" (like a syringe) like a HEUI injector...they merely open to let fuel out..and close to block fuel flow through the nozzle...but they never are EMPTY of fuel...

and doesn't have to refill each, individual injector...between each injector firing.

the plunger spring IS going to force the plunger back to "TDC"...and if there isn't sufficient positive fuel pressure (regardless of volume)...the barrel cavity can entrain some air...especially with lower pressure at higher engine rpm.
 

Tom S

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Fuel pressure is more important to the life of the nozzle than to power loss. Think about how hard that nozzle needle hits it's seat. When fuel pressure is down there is less cushion. This can cause nozzles to lose flow over time, and in the case of larger nozzles (200%, 400%, & 600%) to crack/break. We have tested fuel pressures from 50psi-90psi and found that 65-75psi is optimum. After 75psi is there is no positive gain. The OBS trucks seem to do fine with 160-170cc injectors or less with the mechanical pump and lower pressures. However any split shot truck or truck running hybrids should try to keep the fuel pressure > 60psi. This is our policy when it comes to injector warranty.

So what pressure would you recommend for a set of OBS Swamps Babies with electric fuel (single SD pump)? I think mine is set for like 64.
 

golfer

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^that pressure will be just fine.

...as long as the pressure is constant/decent under load...

as injector (fuel) demand increases (boost, load, etc)...fuel pressure could drop.

We typically don't see injector problems (associated with lack of fuel pressure) unless pressure drops below 35psi...

at higher rpm, the lack of pressure (even though it may "have" 35psi)...could cause some lack of lubricity inside the P&B assembly...

rpm plays a huge role... since the TIME between injector firings can get very short (a "refill" period of 40ms @ 3000rpm)

basically..at 3000rpm...the crankshaft moves 90degrees in 5ms...which means AN injector will fire every 5ms...and the SAME injector (#1 for instance) will only have 40ms to REFILL before it has to fire again...not a whole heckuva lot of time to refill with low-ish fuel pressure...

again...high volume LOW pressure pumps (raptor, fass, airdog) don't do so well on HEUI inj systems...since those pumps typically don't produce more than 45psi...though they can have HUGE VOLUME capability...200GPH LOL
 

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