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If you have enough pump pressure, you can make it into the 1000's with a 3/8" line. The line size becomes more an issue when you use a "puller" pump and atmospheric air pressure is pushing the fuel to the mechanical pump. With a pump in the fuel pushing it through the lines this is less of an issue. Cavitation might be a limiting factor, but that's why people put in multiple pumps
That being said, I got SSTUBES to make me a 1/2" fuel line I am going to put on my car eventually
Usually its a pressure issue with the pump, versus fuel delivery
fuel delivery goes down with higher pressure on most pumps. If you had a big mechanical that can generate high volume at high pressure you likely can make alot of power thru the lines. Small return however may be a problem passing the flow of a big pump, but the supply side 3/8” can do some big numbers. I’ve seen posted 1000 hp. On gas thats likely to be true.
walbro pumps start to drop off over 65-70 psi fuel pressure, so 40-45 psi base plus 20-30 lbs of boost will really start to be the max supply. Two regular 255’s can flow enough for 1000-1050 whp, but to keep that pressure down go to a 1/2” or -8 an line
i can tell you this, on a 4th gen tank that has a 3/8” outlet, even 3 pumps wouldnt go over 1100 whp on my old setup. That small few inches of -6 / 3/8” line, even tho it expanded to -8 to the rails, was too small.
So i would think an entire span of 3/8” would suffer much more pressure loss, and thus be difficult to get high hp using typical intank walbro pumps or even aftermarket external units. They all suck at high pressure, short of a 5gpm aeromotive brushless. They will still have enough volume i think at lower pressure to overcome the small line to a point.
idk what ur goals are. So that will determine what you should do next lol
358 sbc with about 12-14 psi jammed down its throat. 60lb injectors. Currently has a single 255 pump with hotwire. I thought about a boost a pump. But not sure. If im better off with just a bigger pump.
Depending on intake and heads/cam that has serious potential for dual 255’s or a single 450. Better to have more pump than not enough obviously but especially on stock lines. I’d be ok with 3/8” line but def have some pump
Depending on intake and heads/cam that has serious potential for dual 255’s or a single 450. Better to have more pump than not enough obviously but especially on stock lines. I’d be ok with 3/8” line but def have some pump
Ok. So better off with a 450 tban a boosta pump?
thx
How bout the fuel rails? I don’t think I’ll be makin enough steam to warrant up graded lines or rails, but I’d rather do it now then have to tear it apart again
The limit with the lines is really the return line. You can force a lot of fuel through the 3/8" line, but the return has to return most of that at less than half the pressure at idle or your fuel delivery gets uncontrollable (when the pressure starts going up significantly in the return, the pressure in the feed goes up above what the regulator is set for making tuning difficult).
As far as fuel rails, flow isn't really the problem, it's pressure drop when a really large injector opens. For the most part, if you Y the inlet and outlet, run them in parallel instead of series if you were talking about an electrical circuit with the fuel pressure regulator after the Y you can flow a TON of fuel even with moderate-sized rails.
So say I'm running a Holley carb at only 5-7 psi (fuel pressure) with a return style AFPR.
Still using the stock TPI lines, a Walbro 255 pump would probably max out the return line or not?
That is quiet a bit of fuel needing to return on such a small line.
Last edited by bluegrassz; 04-30-2021 at 07:28 AM.
So say I'm running a Holley carb at only 5-7 psi (fuel pressure) with a return style AFPR.
Still using the stock TPI lines, a Walbro 255 pump would probably max out the return line or not?
That is quiet a bit of fuel needing to return on such a small line.
Doesn't matter. Engine uses same volume of fuel at idle no matter how it gets to the engine. The pump is still working at high pressure just like an EFI car.
Pump pressure and regulated pressure are two different things. The fuel pump normally works at a higher pressure than regulated. All the regulator does is bleed off some fuel to the tank to keep the fuel rail at the pressure the engine wants.
The pump has a performance curve. It make the most pressure when the engine consumes the least amount of fuel. The pump pressure (not regulated pressure) drops as the engine uses more and more fuel. Eventually the pump pressure will fall below the regulated pressure and that's when the fuel pressure gauge will show "low pressure". Obviously that happens a lot sooner at 50 psi (multiport EFI) than at 7 psi (carburetor), so the EFI car will run out of pump sooner than the carbureted car because of ability to deliver flow @ pressure. Basically the lower operating pressure of the carb extends the operating range of the pump.
Doesn't matter. Engine uses same volume of fuel at idle no matter how it gets to the engine. The pump is still working at high pressure just like an EFI car.
Pump pressure and regulated pressure are two different things. The fuel pump normally works at a higher pressure than regulated. All the regulator does is bleed off some fuel at the pressure the engine wants. The rest goes back to tank.
The pump has a performance curve. It make the most pressure when the engine consumes the least amount of fuel. The pump pressure (not regulated pressure) drops as the engine uses more and more fuel. Eventually the pump pressure will fall below the regulated pressure and that's when the fuel pressure gauge will show "low pressure". Obviously that happens a lot sooner at 50 psi (multiport EFI) than at 7 psi (carburetor), so the EFI car will run out of pump sooner than the carbureted car because of ability to deliver flow @ pressure. Basically the lower operating pressure of the carb extends the operating range of the pump.
i think for a lot of what you said you were talking about pump FLOW characteristics vs. pressure. for any given pump, it has a graph where it flows a certain amount at the different pressures. they typically flow more at lower pressures. you can run an efi pump at carb pressure, but it may or may not move as much volume as a similar sized carb pump that was designed to operate at the lower pressure. whatever the pressure is at the rail is basically what the pressure will be at the pump. there is some pump controllers and on demand brushless pumps available now that would help out with trying to run small lines. the pump will increase or decrease rpm in relation to engine rpm or need. this would keep a lot of heat out of the fuel and only supply what the engine actually needs which would avoid overwhelming the return line also.
So say I'm running a Holley carb at only 5-7 psi (fuel pressure) with a return style AFPR.
Still using the stock TPI lines, a Walbro 255 pump would probably max out the return line or not?
That is quiet a bit of fuel needing to return on such a small line.
I'm running a Holley black pump on my turbo truck with 1/2" line. The pump makes 14psi. I couldnt get the pressure to drop below 10psi til i went with 5/8" line. Big differences between flow, volume, and pressure. I'm still learning.
Ok, so say I am staying carb for now but may swap to Sniper efi later. I am currently needing to replace my pump, so should I source a pump that will run the sniper. Using my current carb bypass regulator to reduce it to 6 psi. Then if I swap to the sniper it has a built in regulator for the efi.
Would this plan work with the stock supply/return lines? Not really wanting to pull the tank again. Just trying to make the smart move while it is currently out.
Thinking of this pump?
Kenne Bell BAP at 17.5V increases output of a Walbro 255 L/hr pump by +100 L/hr. So basically makes it behave like a 340 pump.
I wonder if that may or better if the boosts pump is activated by boost. The 255 flows more than enough under most conditions, boost a pump makes up any shortfall under boost. Vs a 340 pushin all that fuel even when it’s not needed. Just a thought.
Thanks
That's up to you. The BAP has a 17.5V setting and a 21V setting that ups the pump output even further. Running a Walbro 255 at 21V will ruin it in a hurry and even Kenne Bell will tell you that. Seems a lot of people have success at 17.5V. My own LS1 style Racetronix 255 LPH pump failed very soon after installing the BAP. Coincidence? I don't know, but my BAP is sitting on a shelf now. I wasn't trying twice.
If you really need crazy, I think Vaporworx has a PWM controller that will work with the BAP so you only get the increased voltage when your engine demands the higher flow. Kind of the best of both worlds, all the pump, plus the boost, none of the extra wear on the pump when not needed.
More voltage pushes the pump harder and it can move more fuel. It also kills the pump sooner because you're pushing it harder. At some point, the coils start overheating and will burn out, or you exceed the limits of the bearings... all of which are fuel soaked/cooled so you're getting that hotter also.
More pump moves more fuel without working harder, but it does make dealing with the fuel flow at lower power levels more challenging.
Staging things is the best of both worlds, but if you do it using something like a hobbs switch or the ecm turning a second (or third) pump on at a specific RPM, boost..., the additional flow doesn't happen instantly so you have to be careful how you do it, not enough fuel under high boost = engine go home in bucket.
I'm not really sure what it gets you. I swapped a '98+ plastic tank with one of their 340 pumps for MUCH less than that, and although it uses different style fittings they are easily adaptable and the same size.
04-26-2021, 10:24 AM
