In-line Fuel Pump

Procision-Auto · Post by **Procision-Auto** » Fri Jun 02, 2006 10:58 am

I have a problem with understanding the efficiency, and benefit of using
an in-line fuel pump in series with a stock in-tank pump as opposed to an auxilary pump in parallel with the stock in-tank pump.

A friend of mine is using a Paxton in-line fuel pump (for a turbo application)
in series which apparently pulls fuel through the stock pump.

Will this not create a flow restriction, and load down the inline pump?

KennyM · Post by **KennyM** » Sun Jun 04, 2006 11:35 pm

Most in-line pumps are not meant to be pullers very far from the tank hence the low pressure intank pump to feed them.
Ford used this system thru the 80s into the 90s on many Bronco/Ranger and truck applications while car applications from about 87 up went to the full hi pressure intank pumps.
The pump capacity was often matched with the engine power and with quite a bit of reserve volume capacity to spare.
Example of Ford 5L is an 88 l/hr pump to feed a 225 rated engine but will actuallty supply enough fuel volume for close to 290 hp.
In blower application, this same pump is forced to feed enough fuel to provide close to 300 hp by using an FMU in the the return line to raise pressure drop accross the stock 19 lb injectors , but this is about the limit using 7 to 8 psi boost pressures before having to install a larger volume pump.

KennyM · Post by **KennyM** » Mon Jun 05, 2006 1:45 pm

I neglected to mention that these type pumps have an inverse relationship of pressure ver. volume.
As you raise the pressure the pump works at, the lower the volume pumped.
From this you can see that if you forced a pressure of say 80 psi by restricting the return, the volume pumped cannot be very high.
Usually the volume rating on any pump is pegged to some standard restriction (regulated pressure) in the application.
For Ford 5L it is usually 39 psi.
This is also the same pressure the fuel injector flow is referenced to.
There are injector tables that reference injector size to ability to feed a known HP level at the specified pressure drop.
With this information you can size a pump and injectors for any reasonable known amount of HP and also consider BSFC numbers in adjusting the sizes especally when they fall near capacity limits before considering the next larger or smaller sizes..
Other considerations are blower applications that should consider BSFC higher than N/A applications as well as overall combustion efficiency of the specific engine etc. These are ususally dyno items for determination.

Procision-Auto · Post by **Procision-Auto** » Mon Jun 05, 2006 1:48 pm

Good info, thanks for the read.