Thread: Whats your fuel Pressure?

I remember reading that Miko said the walbro makes the car run at something like 52psi base pressure with no afpr. People buy the Nismo or whatever else just to drop it down to 3 bar. But how many people are running something other then 3 bar? Cause as long as you have something to compensate for the extra fuel why are we stuck at 3 bar or even four bar base fuel press?

I was also reading about someone saying in another thread why not take the 370's past four bar base since they can obviously handle it.

Cause at 43.5psi + 20psi of boost your sitting at 63.5psi of fuel pressure at wot. If my Injectors run fine at WOT and 63psi. Wouldnt it be the same thing as the 52psi the walbro bumps the FP up to with the stock FPR and say 11lbs of boost?

Im just trying to see why the afpr is even needed if you have something to tune out the richness and your Injectors can handle it. Ive done up to 22psi at 3 bar FP with these RC750's. Thats 65.5 psi. Im only trying to run about 1 bar of boost so thats around 66.5psi with no afpr. I think the injectors can handle that. But am I missing something from the equation that makes my math off?

Alrighty then!

Thats the whole point he was saying, If your on a jwt ecu or calum basic or whatever that is programmed for 3 bar fuel pressure and dont have a way to adjust for the higher that your car will run rich. Which is true and verified. If you have something like a realtime or safcII or whatever to adjust fuel then its fine. It doesnt have to do with pressures being too high for the injectors. You can run 4 bar base pressure and 30psi of boost which ends up being basicly 90psi and not have problems with the injectors as long as your using a good set. My venom 740's had no issues with it.

My ID1000's I was running I was running a 65psi base pressure and 35 lbs of boost so roughly 100 psi of fuel pressure. But ID injectors can actually run at a 100 psi base pressure and then up to 150 psi total pressure before they have problems getting stuck open or closed.

I wouldnt run any more than 60psi base on any sidefeed injector out there. I dont think they will like over 100psi fuel pressure. Dont know how many have experimented with it before all I know is what I ran through my venom 740 sidefeeds and they were fine.

With my ID2000's I plan to run 3 bar base pressure only because the max recommended pressure for my fuel pump is 95 psi and I plan to run up to 40psi of boost so yeah, got to keep the fuel pressure down to avoid issues and keep it within parameters.

I'm highly skeptical of this, and I even have a little bit of data to back up that claim.

I wanted to say here that yes, you're absolutely correct with this.

I've never used, nor ever recommended an adjustable fuel pressure regulator. I think they are stupid as can be. If you want to run 3-bar base pressure, use the stock FPR. If you want to run 4-bar base fuel pressure, buy a damn 4-bar FPR.

No, you're not missing anything. You're perfectly correct.

So ash would this also apply to msd style injectors also? I understand your speaking from your experience on your set up but I am just curiuos because I plan on running msd 72lbs injectors in my setup I will also be using a jwt tuned ecu.

I installed a Walbro 255 HP a while back and my car has been running slightly rich ever since. I installed a fuel pressure gauge before I installed a Nismo AFPR and my pressure was right around 50 - ~55PSI with the hose off.

The experience I had was simple. N/A engine with stock injectors, fuel pump and FPR. The fuel was tuned with a stand-alone ECU and everything was perfectly where I wanted it. I then installed the Walbro 255 lb/hr high pressure fuel pump and fueling changed so little in all areas that I didn't touch the tune at all.

Now, those with proper fuel pressure gauges are showing higher base pressures... Okay fine. That higher pressure condition should manifest itself at idle only. Once you go above idle your pressure should be identical to stock since the only reason pressure would rise is if the return line is overwhelmed by the higher flowing pump. Above idle the return line should no longer be overwhelmed because the injectors are letting off enough pressure for the FPR to do its job properly.

planning on running 5bar on my deka top feeds eventually

Ben has it right on point, the return line will overwhelm with a high pressure pump. You have to think also the stock regulator was designed for the fuel system size it came with. When I was first testing my walbro intank to bosch 044 inline, 1/2" feed w/ -8 hoses and fittings and then using a -6 return line to the stock se-r fuel feed and now using it as a return and with no regulator on and the pumps kicked on I was seeing 15psi of fuel pressure all because of the return line restriction. So I fully understand this concept.

As for the MSD injectors. Its pretty common knowledge that they recommend no higher than 3 bar base fuel pressure on them because they do not have very strong coils and are a cheaper injector made with cheaper parts and will have problems at any higher. And this is to give you room for rise of pressure during boost. Id stick to 3 bar.

5-bar base plus tons of boost would have me very worried about pressure-locking the injectors. Just make sure they are up to it.