Sorry, Another Fuel Pressure Thread - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

BlazedGlory · 03-03-2007, 05:58 PM

For some reason today I decided to do some research on what fuel pressure I should be running, but I can't find exactly the answer(s) I'm looking for. I realize fuel pressure should be 43.5psi with no vacuum to the FPR on a stock SR. I found out that too much pressure can cause the injectors to behave erratically, yet I did not find out how much "too much" is.

My question is: on a SR20DET engine, is it always best to set your vacuumless FPR to 43.5psi? What if you have a highly modified engine? What if you have aggressive cams that reduce your vacuum at idle? Would more or less pressure reduce/increase the efficiency of the fuel system assuming you could tune to the same AFRs (edit: slightly OT thought: people used to set up paintball guns to run lower pressure to increase the amount of shots they could get out of a given tank. Basically a lower pressure, but larger volume of air would project the paintball the same velocity. Only downside was if you decreased the pressure too much, you would lose velocity during rapid fire situations [FPR couldn't keep up]. Could this be like the car leaning out at high RPMs if the pump couldn't keep up?). Would it ever be necessary/a good idea to run more or less fuel pressure assuming you have the proper tools to tune to the proper AFRs regardless of pressure? Does it not really matter at all as long as I don't run too much pressure (whatever that limit may be)?

My fuel system consists of a Wahlbro 255LPH pump, Sard 850cc injectors, and a Nismo FPR on the stock rail (yes I know the pump can't keep up, but I'm not near maxing the injectors). I have a PowerFC and an Innovate wideband setup, so I can tune my AFRs. I'm running HKS Step 2 264s.

Help me understand how to decide where to set my fuel pressure and why (other than "Nissan specification is 43.5psi").

Thanks

cotbu · 03-03-2007, 07:59 PM

it's the standard
so when the injectors are static they will flow 850cc
If they went static and your fuel pressure is 20psi they will not flow 850cc

Now if you increase the presure they will flow more as injector perform better when pressure is increased, IIRC let's say +10psi, so your now static and your injectors flow 932cc
just a example

someone maybe able to explain better but this i my understanding of fuel pressure in a nutshell

03-03-2007, 05:58 PM	#1
BlazedGlory Zilvia Junkie Join Date: Jan 2003 Location: Canton, GA Posts: 370 Trader Rating: (1) Feedback Score: 1 reviews	Sorry, Another Fuel Pressure Thread For some reason today I decided to do some research on what fuel pressure I should be running, but I can't find exactly the answer(s) I'm looking for. I realize fuel pressure should be 43.5psi with no vacuum to the FPR on a stock SR. I found out that too much pressure can cause the injectors to behave erratically, yet I did not find out how much "too much" is. My question is: on a SR20DET engine, is it always best to set your vacuumless FPR to 43.5psi? What if you have a highly modified engine? What if you have aggressive cams that reduce your vacuum at idle? Would more or less pressure reduce/increase the efficiency of the fuel system assuming you could tune to the same AFRs (edit: slightly OT thought: people used to set up paintball guns to run lower pressure to increase the amount of shots they could get out of a given tank. Basically a lower pressure, but larger volume of air would project the paintball the same velocity. Only downside was if you decreased the pressure too much, you would lose velocity during rapid fire situations [FPR couldn't keep up]. Could this be like the car leaning out at high RPMs if the pump couldn't keep up?). Would it ever be necessary/a good idea to run more or less fuel pressure assuming you have the proper tools to tune to the proper AFRs regardless of pressure? Does it not really matter at all as long as I don't run too much pressure (whatever that limit may be)? My fuel system consists of a Wahlbro 255LPH pump, Sard 850cc injectors, and a Nismo FPR on the stock rail (yes I know the pump can't keep up, but I'm not near maxing the injectors). I have a PowerFC and an Innovate wideband setup, so I can tune my AFRs. I'm running HKS Step 2 264s. Help me understand how to decide where to set my fuel pressure and why (other than "Nissan specification is 43.5psi"). Thanks

03-03-2007, 07:59 PM	#2
cotbu Post Whore! Join Date: Sep 2005 Location: SWFL Age: 50 Posts: 3,318 Trader Rating: (3) Feedback Score: 3 reviews	it's the standard so when the injectors are static they will flow 850cc If they went static and your fuel pressure is 20psi they will not flow 850cc Now if you increase the presure they will flow more as injector perform better when pressure is increased, IIRC let's say +10psi, so your now static and your injectors flow 932cc just a example someone maybe able to explain better but this i my understanding of fuel pressure in a nutshell __________________ LoverTechnologies "Half Broken Things!"