C409

........... Can I use the in-tank pump as a pusher for an externally mounted pump ? .....

John A. Marker

You could. But you should do some research.....most in the tank pumps (85 and newer) are made to feed the fuel injectors and are pushing 40-60 PSI from the pump to the FPR. Most external pumps are designed to feed carburetors that usually require only 8-12 PSI.

For FI cars, you have a return fuel line going from the FPR to bleed off the excess fuel supplied by the pump back to the tank. The carburetor feed engines usually have a float valve that shuts off the fuel supply to the bowl and no return line.

C409

........... This would be used to push fuel to an EFI external pump ... just looking to over-feed the rails ... depending on mounting location , which is somewhat limited on the Corvette , a lift pump is almost a necessity to feed an external pump ... its my understanding that EFI pumps are not as efficient pulling fuel as they are pushing it ...... carbs are for classic cars anyway ... not for C4s ........

John A. Marker

I am by no means a expert on fuel pumps. But wouldn't a Walbro 255LPH in tank pump provide enough pressure for your system?

C409

..... Perhaps ... I'm no expert either , but , I have a high flow pump in the tank now and I also have a high flow external that's currently lounging around on the shelf ... I want to put the slacker to work even if its redundant ... the reason I'm asking is that I didn't want to defeat the purpose for some un-thought of reason ....... I am hoping someone else may have done this and would share their experience ........ being a long holiday weekend this is the only place I felt I could expect some expert advice ..................

WW7

Last time I talked to Pete K, he was running 2 pumps the same as your discribing for his 421. It seemed to be working for him....WW

QZRBLU

You can use this calculator with your values and back up to the LPH needed to feed YOUR engine with YOUR size injectors.

http://www.fuelinjectorconnection.co...widercalc.html

Mick

383vett

I have an external Accel beer can pump mounted in front of the fuel cell. It sucks and pushes enough to maintain 46lbs and have plenty of fuel to run 10.30s.

C409

............ You also have a bottom sump in your fuel tank ... I'm running the factory fuel tank and an external pump would need to draw fuel up and out of the stock fuel lines ... I do believe there's a pretty good reason the mfr's all want to put EFI fuel pumps IN the tank ... what I am interested in doing is providing an overkill fuel supply to my engine with parts already owned ...... Is there some reason why my intention wouldn't work ? ... I really wasn't looking for alternatives ... just enlightenment ..........

vetteoz

Flow rate of the two may be mismatched ;so ext pump is trying to suck through tank pump ( a restriction )
or in tank pump is trying to pressurize ext pump ( a restriction ) pumps require fuel flow for cooling

I suspect the only way to make it work properly would be to have the in tank pump feeding a surge tank ( like the ricers !) with a return to the tank
so it operates completely independent of the ext pump and the tank then supplies the prime for ext pump.

383vett

I was running this same setup when I had the stock tank in the car. The fuel pump intake was hooked up to the stock fuel line coming out of the tank. Within the tank, I replaced the stock pump with a length of braided fuel line with a sock on the end. This pump was able to pull fuel out the top of the tank and into the motor with no problems. Remember, if the pump is mounted below the tank, the fuel will essentially siphon out of the tank without needing to be sucked out.

C409

......... Cool ......... But can I use the in-tank pump as a pusher for an externally mounted EFI pump ? .........

383vett

I've heard of some doing that with no problems.