Fuel pump/module question

[Kris396ss]

Hey guys, I'm working on a very budget fuel pump module that'll support 650+WHP on E85 (or more with a boost-a-pump) using a Walbro 525LPH pump and my own custom bucket. I'll post more about that when it's finished, but I just have a question and haven't been able to find a clear answer.

How exactly does the factory viper pump work? What I mean is, I know from posts i've read that is uses a "secondary" inlet to draw fuel from within the tank into the bucket, but is that inlet using direct suction from the pump or does the secondary inlet generate suction via a venturi inside the pump using primary inlet is its pressure source?

If the latter, what happens if the bucket/tank runs dry, how would fuel re-enter the bucket once filling the tank again if there's no fuel left IN the bucket for the primary inlet to create that venturi effect with and draw more fuel in?

I haven't found anyone who could answer this. Should be relatively easy to figure out if I had a factory Viper pump and bucket, but my car never came with one so I don't have one to look at.

 

[GTS Dean]

It's the center venturi section of the pump that extends below the bucket and draws from the tank. As long as there's 1-2" of fuel in the tank, it will prime.

 

[Kris396ss]

So in the event that fuel sloshed away from the secondary pickup starving it , and the bucket ran dry (say on a hard, long turn) , the secondary pump could still generate suction to refill the bucket once it became covered with fuel again? I would think it may take a little while to do so as i can’t see the Venturi effect being too strong when the primary inlet is just sucking air , assuming there is no other way for fuel to enter the bucket.

 

[GTS Dean]

You are correct. Have you read the 850 hp sticky thread at the top of this sub-forum?

 

[Kris396ss]

I have! It was a great write up, just didn’t go into enough detail about how exactly the Venturi worked for someone who doesn’t have the actual pump module to look at like myself lol but you cleared that up for me.

I think what I’m confused about is with what I described above, how would that not create a problem if in the rare event it occurred in track and you managed to run the bucket dry? Being that the pump only primes for a short burst with key on, it seems like it would be very difficult to fill that bucket back up to where the primary inlet has ample fuel coverage to start the car back up again.

I know it’s probably a very rare scenario, but just trying to see how the factory setup would work in that event to address that potential issue with my own custom bucket.

I decided to take a slightly different path from that sticky thread and threw together a real budget pump module using one way check balls that should support 650+whp on e85 and my out of car testing seems to show some promise as to it controlling fuel well enough on a road course. I’ll post a whole video/write up of it as soon as I get a chance, but I wanted to explore one other idea I had using a Radium Venturi t fitting off the return (I’m using a bypass regulator/return system). That’s where understanding how the factory did it comes into play. I have concerns with using that method of whether or not the siphon could keep up with fuel demands on a higher Hp setup and with no other mechanism feeding the bucket, you could potentially starve for fuel even with ample fuel in the tank.

Other issue being the one I originally posted about what happens if in the rare event the bucket and siphon pickup run dry.

 

[GTS Dean]

Then you're plumb out of gas. You put a few gallons in, cycle the key on/off several times to prime the pump and injector rails, then fire it up.

 

[Goggles Pizano]

We have seen your book of faces posts with pictures of the pump.

 

[Goggles Pizano]

Why would you duplicate the pump design instead of engineering something better that fits the housing?