Fuel Flow Capacity of Return Line...EXPERTS please

[jspaeth]

My good friend has an R33 that we have done a Full Race GT35 conversion on....

Long story short, he is converting from stock 6x370cc injectors to 1000cc injectors.

He is installing an external Bosch 044 Pump (200 lph) in series with a Walbro 255 lph in-tank pump.

He wants to run a -6AN line from the pump to the fuel rail, but then he plans on using the STOCK return line.

I have told him that this worries me.

I am worried that the pump/feed line will be flowing a BUNCH of fuel, but the stock return line will be too restrictive...

Figured this would either overwork the pump, or lead to backpressure that could fuck up the FPR's ability to do 1:1 or also it's ability to restrict fuel (provide a SMALL enough quantity of fuel) at low RPMs and under vacuum.

What do you guys think? Does he need to also run a beefier return line? Or will he be okay with the stock return line...?

[Prez]

fuel is being "consumed" so not all the fuel going to rail is going through the return. you might have to compensate for the stock hardline when setting your FPR it may benefit if it increases FP under boost/ High flowing... it can be done just has to be compensated for.... a higher flow return would be easier to tune and prob a better idea long term... nvm the stock is prob dirty and old and burst pressure is prob reduced alot from age alone.... you put all this work in i would upgrade

[jspaeth]

fuel is being "consumed" so not all the fuel going to rail is going through the return. you might have to compensate for the stock hardline when setting your FPR it may benefit if it increases FP under boost/ High flowing... it can be done just has to be compensated for.... a higher flow return would be easier to tune and prob a better idea long term... nvm the stock is prob dirty and old and burst pressure is prob reduced alot from age alone.... you put all this work in i would upgrade

At idle/low revs/vacuum situations, you are literally probably using 1% of how much the pump is pumping, so the other 99% is going back to the tank.

....so that pretty much negates what you just said....

[Prez]

:duh:

nvm the stock is prob dirty and old and burst pressure is prob reduced alot from age alone.... you put all this work in i would upgrade

this still stands IMO i would upgrade if its even being questioned... its your investment...

[greenman100]

My good friend has an R33 that we have done a Full Race GT35 conversion on....

Long story short, he is converting from stock 6x370cc injectors to 1000cc injectors.

He is installing an external Bosch 044 Pump (200 lph) in series with a Walbro 255 lph in-tank pump.

He wants to run a -6AN line from the pump to the fuel rail, but then he plans on using the STOCK return line.

I have told him that this worries me.

I am worried that the pump/feed line will be flowing a BUNCH of fuel, but the stock return line will be too restrictive...

Figured this would either overwork the pump, or lead to backpressure that could fuck up the FPR's ability to do 1:1 or also it's ability to restrict fuel (provide a SMALL enough quantity of fuel) at low RPMs and under vacuum.

What do you guys think? Does he need to also run a beefier return line? Or will he be okay with the stock return line...?


Stock will be fine. He's not increasing flow significantly, just available pressure.

Also the bosch pump is pretty useless in series, he's allowing for double the pressure but actually a reduced flow.

Aren't you studying to be a MechE?

[jspaeth]

I'm getting my PhD in ChemE (only about 1.5 more years!) and this is just basic fluid mechanics, but my friends never wanna listen to me....