Why high fuel pressure on P7100?

XTrEmE9156 said:
should have more.. factory spec is higher. 20 idle and 40 high idle.
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do u think i need a bigger fass pump? i was running 15psi with my VP and got the new spring from fass and now have 25-26 and thought id be safe. even at WOT it stays around 25
 
As long as you're above 20 at full load i would say it's fine. Unless you want more.
 
Under a load you will def. find a increase in power at say 50# rather than 20-30#.
 
stock600 said:
Under a load you will def. find a increase in power at say 50# rather than 20-30#.
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good lord 50 lbs of fuel pressure? the only way i can see that is if i bought a fass 250 and put some serious springs in it
 
the higher the low end fuel pressure the more efficiently the pump will work. having more low side fuel pressure helps charge the barrels with fuel faster, but its more pronounced at higher rpms and high fuel load applications. the same logic applies to duel feeding, it helps the barrels recover fuel when theres a high fuel demand. at high rpm, high fuel flow operation theres less time for the fuel charge to enter the barrels, so more flow (duel feeding), and more fuel pressure will help the pump out.

im sure theres power to made from higher fuel pressures but my guess its thats it not nessicarily giving it more power so much as its making up for the power lost through inefficiently charging the barrels. i would guess it smooths out engine operation and fuel injection pulses which could lead to gaining some lost power due to inefficiency like i said. thats my .02
 
SootKing said:
good lord 50 lbs of fuel pressure? the only way i can see that is if i bought a fass 250 and put some serious springs in it
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50#? First time I streched the stock spring in a OFV it pegged a 100# guage at idle with just the stock mech. lift pump. Getting the pressure is easy it's mantaing it under load thats the issue when hp increases. Like others have said I see no reason to ever go more than ~ 45/50 psi, but that needs to be keep close at WOT and under a serious load or power will drop with it. Ryan
 
2Tone12V said:
AirDog has a 250 gph pump that I used on my puller this year. Stuckeys use it in their drag truck and Kusileks use them in their trucks as well. All of them hold 45 psi with only a 1-2 psi drop. You then have the luxuries of your filter system, plenty of volume, the pressures needed, and of course the air removal to make the injection system work consistent. Cause with all that return fuel you are creating tons of foam in the tank that just gets shoved through the injection system.
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mine is set at 32-33 and never drops...not on the dyno nor on the track. probably had it is way over 4000 rpm, but not sure due to the gauge.

it's an amazing pump!!!!
 
SHughes said:
mine is set at 32-33 and never drops...not on the dyno nor on the track. probably had it is way over 4000 rpm, but not sure due to the gauge.

it's an amazing pump!!!!
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This is good info. are you running a regulator with it to hold that 33# or is that wide open? Have you played with a touch more pressure say 45# to see if you have a gain. I'll be testing in the morning but Ive lowered my idle pressure from ~75 to 50 and so far Ive not seen it drop a single pound at either setting; it is a Lot of fuel returned back to the tank though for sure.......
How is you pump priced as to compair with my A1000 mine was right at 300 bucks. I hope it does a good job and works a long time.........
Ryan
 
we run a fass 150/200. i have a flow control on the return line as it goes back in to the cell. i can turn it up or down from there. the best setup we have found is 70psi at idle and that will pull down to 60psi @5k rpm. that is feeding 3/4" line to a y fitting then two 1/2" lines feeding 2 ports on the p-pump.
 
Why strain the pump with such Hi PSI at idle ? I used to do this till I killed a pump or too now I use a boost reference regulator now its 20 idle and goes up to 70
 
i went the mechanical route and made a plate to mount an aeromotive belt driven fuel pump where my a/c used to be. i can get upwards of 70psi at idle alone. my regulator is on the return line and im going to run about 40psi at idle and should be able to crank out about 100psi at WOT. at 5000rpm, i noticed the motor seems to sound better with the very high fuel pressure but i dont know how much i gained from it and i havent hooked it yet.
 
I ran my stock LP up to around 560hp it pulled down to 7psi WOT Installed an Air Dog 150 and Dynoed again made 20hp more @ 33psi WOT. Spill port fill time and cavitation have alot to do with needing added pressure and volume. Go to low like were I was at and you run the risk of sticking a plunger as well.
 
stock600 said:
50#? First time I streched the stock spring in a OFV it pegged a 100# guage at idle with just the stock mech. lift pump. Getting the pressure is easy it's mantaing it under load thats the issue when hp increases. Like others have said I see no reason to ever go more than ~ 45/50 psi, but that needs to be keep close at WOT and under a serious load or power will drop with it. Ryan
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i did something similar but i changed out the shims and doubled the spring with another one out of a second overflow valve. i got it to where it was like 75# at WOT i took out the one spring and played with the shims and got it to where i was about 50# and dropped to maybe 30#. that is running a holley blue pump into a mechanical LP off an 8.3 c-series engine. with that set up the holley only running about 11# and the small volume that a gas pump runs and the stuff in my sig i am about 500hp at the rear wheel. i imagine i can get more with a high volume pump but too cheap and satisfied with what i got for now.
 
I shimmed the spring in my Air Dog last night and got it at like 50 psi at idle, and goes to 55-60 WOT,... Is that too much ? I figured the spring might compress back a little seems how i stretched it a little and would settle around 40-45 at idle ?? What do you guys think ?
 
Little off topic BUT,

By stretching the OFV spring what is this doing? Returning less fuel to the tank?


my truck has a problem running out of fuel at 2800-3000 rpms under WOT.
 
murphy41 said:
I shimmed the spring in my Air Dog last night and got it at like 50 psi at idle, and goes to 55-60 WOT,... Is that too much ? I figured the spring might compress back a little seems how i stretched it a little and would settle around 40-45 at idle ?? What do you guys think ?
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How do you have more pressure at WOT than at idle? Are you still using the stock pump or a boost referenced regulator?
Once you start stretching the springs they will weaken sooner but if you didn't stretch it much it will be a long time before it weakens.

YOUNG GUNS15 said:
Little off topic BUT,

By stretching the OFV spring what is this doing? Returning less fuel to the tank?


my truck has a problem running out of fuel at 2800-3000 rpms under WOT.
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Are you running out of fuel pressure? Or is the rest of the engine coming up short?

If you stretch the spring then it takes more pressure to open the valve. You still get the same volume returned to the tank (under most circumstances), you just work the LP a little harder and get more pressure.
 
stock600 said:
This is good info. are you running a regulator with it to hold that 33# or is that wide open? Have you played with a touch more pressure say 45# to see if you have a gain. I'll be testing in the morning but Ive lowered my idle pressure from ~75 to 50 and so far Ive not seen it drop a single pound at either setting; it is a Lot of fuel returned back to the tank though for sure.......
How is you pump priced as to compair with my A1000 mine was right at 300 bucks. I hope it does a good job and works a long time.........
Ryan
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I'm running Airdogs Demand Flow 200...it's a bit more than your set up, but worth every penny.

I didn't have a chance to try raising the pressure out of it before the motor went back to the machine shop, but I'll be trying it when I get it back.
 
murphy41 said:
I shimmed the spring in my Air Dog last night and got it at like 50 psi at idle, and goes to 55-60 WOT,... Is that too much ? I figured the spring might compress back a little seems how i stretched it a little and would settle around 40-45 at idle ?? What do you guys think ?
Click to expand...

Pure Flow (AirDog) has an upgrade spring to run 45psi for a 12v.
 
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