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Curious if any high horsepower users are doing deadhead fuel rails with the regulator pre-fuel rail?
Looking at this quite frequently on high power LSX engines and Ford's....they seem to find that with large volume pumps, this keeps heat way down on the return line, stopping all chances of cavitation and necessity for speed control, not to mention, less complex engine bay plumbing
fuel injected is fuel injected. i plan to run a returnless system in my lowly 400hp fc build.
you'll find most call it a returnless system. its the standard way of doing fuel in modern cars as well for no heat from the engine is sent back to the fuel tank.
Last edited by lastphaseofthis; 02-18-17 at 04:11 PM.
fuel injected is fuel injected. i plan to run a returnless system in my lowly 400hp fc build.
you'll find most call it a returnless system. its the standard way of doing fuel in modern cars as well for no heat from the engine is sent back to the fuel tank.
Exactly the same thoughts,
However, keep hearing opinions that the fuel injectors may not receive even amounts of fuel as they open with flow drop across the rail...afraid to be the guinea pig
I don't think you'd be a guinea pig. Any LS already doing it has a bank of 4 injectors inside a single rail.
I think you'd have to do some research regarding how close the regulator should be to the rail. High horsepower applications may require it to be in close proximity vs back near the tank.
I've seen two setups like this first hand. One of which was 3 rotor periph with (I think) 1300cc injectors. Fuel pressure fluctuation was so bad I refused to even try to tune it. The other was on a street port that seemed to work well under load, but couldn't idle below 1100 to save its life.
I don't see much point unless you're actually having issues with overheating fuel.
that what works for some cars may not work for others. boingers for instance, usually aren't running nearly as much fuel requirements as rotaries so they may get away with it.
keeping the work as minimal as possible i was going to put the FPR at the tank, and have the smaller OEM return line turned into the feed line for the primary injectors, and the original feed line going to 2nd injectors, with the ends of the rails looped to each other.
basicly making the factory feed and return becoming dual feed to rails...
in the tank, a stock pump and a wb460 tee'd together, factory runs all the time, wb460 kicks on higher loads. thinking an "off"" walbro460 will hold stock fuel pressure against it's outlet...
If you are running returnless, your ECU needs to account for this. You need an ECU that is set up to run a returnless fuel system. In an older style return system, the pressure in the rail is maintained relative to atmospheric by the vacuum hose on the regulator. In a returnless, port injection engine the rail pressure is not held constant relative to manifold pressure. ECU calculates a compensation factor to the injector pulsewidth based on the pressure ratio.
Translation: this will NOT work with your standard Power FC or other ancient standalone.
If you are running returnless, your ECU needs to account for this. You need an ECU that is set up to run a returnless fuel system. In an older style return system, the pressure in the rail is maintained relative to atmospheric by the vacuum hose on the regulator. In a returnless, port injection engine the rail pressure is not held constant relative to manifold pressure. ECU calculates a compensation factor to the injector pulsewidth based on the pressure ratio.
Translation: this will NOT work with your standard Power FC or other ancient standalone.
Thanks for the clarification and documentation, you rock!
Not really sure what to trust, but according to this guy, he has no issues, with regulator pre-fuel rail, running 2x walbro 450's on boosted application
Really keen on trying this as just an expirament for future builds, just need a regulator that accepts 2 inlets, as the 529 series I'm using is a in/out design unlike most regs
That last guy, Malcolm V8, is a little off. Trying to control rail pressure exclusively by changing the speed of an electric pump in the back of the car (usually in the tank) doesn't work. That's a bad idea from day 1, no wonder he had problems. We are arguing over semantics here, but what he's talking about is not a "returnless" system in the normal sense of the word--not in the world of fuel systems (maybe meth injection though).
Look at the OEM returnless fuel systems like the Rx-8. They have multi-speed controls for the pump (maybe a few discrete speeds or continuously variable). The FD has 2 speeds using a resistor, but newer cars have duty control. The actual rail pressure is still set by some kind of relief-style valve though. On a return system, the relief valve is in the engine bay, and the extra fuel flows all the way back to the tank. On a returnless system, the relief valve is in the tank, like in the Rx-8 diagram I showed. The extra fuel flows back into the tank, but it makes a short trip (never leaves the pump module basically). In that way, you don't have extra fuel getting hot, which reduces evaporative emissions.
The pump speed only changes to "down speed" in order to reduce electrical load, noise, and evaporative emissions in a returnless system. Which is the same reason it changes on an FD or other return system.
To repeat: You DO NOT try to control rail pressure with by changing the in-tank (or external in-line) pumps speed. They won't respond fast enough, as that guy found out.
The systems that control rail pressure with the fuel pumps apply to direct injection. And even those don't control the pump speed; they have a solenoid that closes a valve to determine the effective stroke of the plunger in the pump. For gasoline applications, the high pressure pump is driven by the camshaft on a piston engine. The speed of the pump is set by the speed of the engine and lobe design on the pump. The ECU never controls how fast the high pressure fuel pump spins. Only the fuel pump spill valve solenoid duty cycle changes the rail pressure.
That last guy, Malcolm V8, is a little off. Trying to control rail pressure exclusively by changing the speed of an electric pump in the back of the car (usually in the tank) doesn't work. That's a bad idea from day 1, no wonder he had problems. We are arguing over semantics here, but what he's talking about is not a "returnless" system in the normal sense of the word--not in the world of fuel systems (maybe meth injection though).
Look at the OEM returnless fuel systems like the Rx-8. They have multi-speed controls for the pump (maybe a few discrete speeds or continuously variable). The FD has 2 speeds using a resistor, but newer cars have duty control. The actual rail pressure is still set by some kind of relief-style valve though. On a return system, the relief valve is in the engine bay, and the extra fuel flows all the way back to the tank. On a returnless system, the relief valve is in the tank, like in the Rx-8 diagram I showed. The extra fuel flows back into the tank, but it makes a short trip (never leaves the pump module basically). In that way, you don't have extra fuel getting hot, which reduces evaporative emissions.
The pump speed only changes to "down speed" in order to reduce electrical load, noise, and evaporative emissions in a returnless system. Which is the same reason it changes on an FD or other return system.
To repeat: You DO NOT try to control rail pressure with by changing the in-tank (or external in-line) pumps speed. They won't respond fast enough, as that guy found out.
The systems that control rail pressure with the fuel pumps apply to direct injection. And even those don't control the pump speed; they have a solenoid that closes a valve to determine the effective stroke of the plunger in the pump. For gasoline applications, the high pressure pump is driven by the camshaft on a piston engine. The speed of the pump is set by the speed of the engine and lobe design on the pump. The ECU never controls how fast the high pressure fuel pump spins. Only the fuel pump spill valve solenoid duty cycle changes the rail pressure.
right I'm with you on this; actually the way it was originally setup on his car is how the factory has it. My buddy has the same issue with his mustang; so he switches to the semi-returnless setup with 2x walbro running full time
Not suggesting to control the pump speed control,
I'm wondering what is likely if one were to run a pump full speed, place the regulator at right at the fuel rail, as close to it as possible, have the fuel return to the tank, but have the rails dead-headed
the thing that pops up as concern to me would be if there ends up being a pressure drop across the injector order
we really need to seperate it into three types of layout.
1. fpr at the rail return system, pump at 100%.
2. FPR at the tank, oem pre 05? aftermarket/custom "returnless", pump at 100%
3. No fpr, oem 2008+ returnless, varible fuel pump.
my point is while arghx does bring up good points, there is a style of returnless system out there that had a fuel pressure regulator in the pump assembly and fuel bled off is just bled right back into the tank without ever leaving. the rx8 does this, lots of subarus do this. i cannot confirm whether or not the fuel pump is varied on the rx8, but i dont remember seeing it in accesstunerrace?.. but they do have FPR in the fuel pump assemblies.. and i know on the subaru the owner/tuner states that most fuel pumps don't like to be PWM, running 100% is the way to go when running bigger turbos injectors and pumps on stis. i work with him and he tunes like 2 a week.
this is why im just moving my FPR to above the tank, and throwing the fuel back in the tank.
Last edited by lastphaseofthis; 02-22-17 at 10:31 PM.
For what it's worth, here's a custom fuel system for a direct injected gasoline V8 engine. The engine is not in a vehicle, it's run on a stand. Of course the fuel pressure among the individual injectors is set by the high pressure fuel system, and runs at max of 15 MPa which is 2175psi.
There is a fuel pump in the building running at 100%. Fuel comes in from the supply line to the regulator. The regulator is in-line and set to a fixed pressure, in this case 460kpa which is about 65psi. After that is a T with a return line and a supply line to the high pressure fuel pump. The fuel rails are in series for the two banks but again the pressure is controlled in that area by high pressure fuel pump. The fuel pump is driven by the camshaft, and the pressure itself is controlled by varying the effective stroke of the pump with a solenoid.
I still think you should try a heat shield, before you consider reworking your entire fuel system. Your naked rails are right next to the naked, high-mount, exhaust.
It's something you could do cheaply, without shipping anything anywhere for coating or engineering anything complex.
02-18-17, 02:41 PM
